View of Abiotic stresses effect on plants physical and chemical events, and role of melatonin against abiotic stresses in regulating plant growth, biochemical traits, antioxidant activities and plant Metabolic System

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Abiotic stresses effect on plants physical and chemical events, and role of melatonin against abiotic stresses in regulating plant growth, biochemical

traits, antioxidant activities and plant Metabolic System.

Zia ul Haq^-1, Nasib Gul^-1, Fazal Munsif^-2, Abdul Malik^-1, Ghani Akbar^-3, Alamgir Khalil^-4 1) Department of Agricultural Engineering, UET Peshawar

2) Department of Agronomy, The agriculture University Peshawar, AMK Campus Mardan 3) National Agricultural Research Center (NARC) Islamabad

4) Department of Civil Engineering, UET Peshawar Abstract

Abiotic stress like drought, salinity, high and low temperature, flood, radiation, heavy metals, oxidative stress, and nutrient shortage harmfully disturb growth rate, quality and productivity of plants. Melatonin as a plant growth regulator was discovered in 1995 in plants and holdup a strong position due to its affect in plants environment. Melatonin shown a considerable character in plant growth response, development, re-production and various biotic stresses. Moreover, melatonin performs a resistive character against stresses like drought, salinity, metal toxicity.

Melatonin important character in plant system is to lighten the harmful effect of abiotic stresses.

In this evaluation we have investigate the effect of melatonin on growth, physiology, photosynthesis behavior, metabolic response, and bio-chemistry of plant under stresses (abiotic and abiotic) environment.

Keywords: melatonin, drought stress, oxidative stress, heavy metal stress, hot and cold stress, salinity stress, plant development, physiology.

Introduction

Inferable from environmental change and outrageous climatic conditions, it is informed that the terrible effect regarding environmental biotic and abiotic stress on plant production will increment in numerous part of the world (Denby and Gehring 2005). Stress factors can concurrently show their effects on plants (kalefetoglu and Ekmekei 2005). About 71% of agricultural product effected by abiotic stresses, while the remaining 29% cause by other stresses. (Boyer 1982). About 10% of area throughout the world is far from stresses. It has been described that more than 50% of yield reduction taking place worldwide due to abiotic stress factors (Mahajan et al., 2005). In the last decade, altered field water supply methods, soil improvement, and the practice of appropriate fertilizers have been introduced so that decrease the influence of stress. As a different tactic, the application of some outside regulator during plant growth has been practiced in recent period, and it has been detected that the application of melatonin (MEL) increasing tolerance in plant against stresses. Melatonin (N – Acetyl – 5 – Methoxytiprimamine) was identified in the year 1958 in the pineal gland of cattle (lerner 1958).

Melatonin is one of the most inspected bio- molecules, which is widely discovered in animals. In plant as an indole amine neurohormones MEL was discovered in the year 1995 (Dubbels et al., 1995; Hattori et al., 1995). Due to performing role in in specific plants physiological pigments MEL considered by many investigator as plant growth regulator (PGR). The natural antioxidant ability of MEL can be described by its aptitude to improve tolerance in plants visible to biotic and abiotic stresses (Amao 2014). Melatonin work as plant bio stimulator for stresses, regulate

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plant growth and perform a probable supervisory character in plant, flowering, production and maturity of fruit. (Reiter et al., 2015; Amao 2014; Nawaz et al., 2016). On the basis of previous research work Table 1 and Table 2, indicates response of melatonin in various plants against stresses and in regulation of various plants antioxidants

Table 1. Role of MEL in oxidative stress and antioxidants regulation in different crop plants subjected to stresses.

Crop Plant Stress Condition

Exo- Melatonin Based Up- Regulated Antioxidant

Exo- Melatonin Based Down- Regulated Antioxidants

Exo Melatonin Based

Variable Antioxidants

Reference

Zea mays L. Salinity POD, APX Jiang et

al., 2016 Cucumis

sativus L.

Salinity SOD, POD, CAT, APX, ASA, GSH

Wang et al., 2016 Malus

hupehensis Rehd

Salinity APX, CAT, POD

Li et al., 2012 Cucumis

sativus L

Salinity APX, CAT, POD

Zhang et al., 2014 Citrullus

lanatus L.

Salinity GSH, ASA, CAT, APX, DHAR,

MDHAR

GSSG, DHA Li et al.,

2017

Zea mays L. Salinity APX, CAT,

POD GPX,

SOD, GR

GSSG, DHA Chen et

al., 2018 Solanum

lycopersicum L.

Salinity SOD, CAT,

GR, APX,

GSH, ASA

GSSG, DHA Sidiqui et

al., 2019 Avena nuda

L

Salinity SOD, POD, CAT, APX

Gao et al., 2019 Coffea

arabica L

Drought CAT, APX

SOD

SOD Campos et

al., 2019 Zea mays L. Drought SOD, CAT,

APX, POD

Ye et al., 2016 Malus

domestica Borkh

Drought SOD, POD,

APX, GSH

Wang et al., 2013 Festuca

arundinacea Schreb

Drought CAT, POD Alam et

al., 2018

Brassica Drought POD, CAT, Li et al.,

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napus L APX 2018

Solanum lycopersicum L

Drought SOD, CAT,

APX, GR,

ASA POD

Liu et al., 2015 Zea mays L Drought CAT, SOD,

APX, GPX AsA, DHA, GSH

GR, GSSG Huang et al., 2019

Tiritucum aestivum

Cold Stress SOD, GPX, APX, GR CAT

GR, GSH

GSSG

Turk et al., 2014 Camellia

sinensis L

Cold Stress APX, CAT, SOD

GR, GSH

GSSG

Li et al., 2018 Oryza sativa

L

Cold Stress SOD, CAT, POD, GSH

Li et al., 2017 Cucumis

sativus L

SOD, GSSG CAT, POX

Marta et al., 2016 Solanum

lycopersicum L

SOD, CAT, APX, POD

ASA, GSH Ding et al., 2017 Zea mays L Heat stress GPX, GR,

CAT

ASA, GSH Li et al., 2019 Actinidia

deliciosa

Heat stress SOD, POD, GR, , ASA, GSH

CAT Liang et

al., 2018 Triticum

aestivum

Heavy metals SOD, APX, GSH

CAT, POD Ni et al.,

2018 Nicotiana

tabacum L

Heavy metals SOD, APX, CAT

Wang et al., 2019 Melissa

officinalis L

Heavy metals SOD Hodzi et

al., 2019 Valeriana

officinalis L

Heavy metals SOD Hodzi et

al., 2019 Cynodon

dactylon L

. Heavy metals

SOD, POD,

CAT, GR,

APX

Xie et al., 2018 Solanum

lycopersicum L

Acid rain stress

SOD, POD, CAT, APX

Debnath et al., 2018 Cucumis

sativus L

Water stress SOD, POD, CAT

Zhang et al., 2013 Malus

baccata L

Waterlogging SOD. POD, CAT

Zheng et al., 2017 Pisum

sativum L

Oxidative stress

SOD Szafra et

al., 2016

Malus Alkaline SOD, POD, Gong et

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hupehensis Rehd

stress CAT al., 2017

Citrullus lanatus

stress SOD, CAT Nawaz et

al., 2018 Arabidopsis

thaliana

High light stress

APX Lee and

Back 2018 Trigonella

foenum graecum L

Lead and acid rain stress

SOD, CAT Xalxo and

keshavkant 2019 Solanum

lycopersicon

Salinity and heat stress

CAT, APX, GR, GST, GPX MDHAR

SOD Martinez

et al., 2018 Cynodon

dactylon L

Salinity, drought and cold stress

POD, SOD, CAT, GSH

Das and Roy

Choudhury 2014

Table 2. research investigation List confirming the effect of MEL on altered antioxidant enzymes at the mRNA level in different crop plants. Upward arrow ↑ shows the up-regulation, while downward arrow ↓ shows down-regulation of genes for enzymes corresponding’s, ± shows variable regulation, and = shows no effect.

Plant Name Genes Name Stress Condition Expression References

Solanum CAT, DHAR ↓

lycopersicon L

Cu / ZnSOD, FeSOD, GR, GPX

Salinity and Heat

Stress ↑

Martinez et al., 2018

GST, APX, MDHAR,

DHAR

Cucumis

sativus L Cu/ZnSOD, CAT, POD Salinity-Stress ↑

Zhang et al., 2014

FeSOD ±

Camellia

Sinensis L APX, CAT, SOD, GR Cold-Stress ↑ Li et al., 2018

Avena Nuda L

NAC, WRKYI, MYB,

DREB1 Salt-Stress ↑ Gao et al., 2019

DREB2 ±

Citrullus Lanatus

SOD, APX, GPX, GST,

CAT Vanadium-Stress ↑

Nawaz et al., 2018

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Malus

Domestica APX

Oxidative-Stress

±

GR ± Ni et al., 2018

POD, MDHAR,

DHAR, CAT ↑

Prunus Persica SOD,CAT,APX,DHAR ↑

APX Oxidative-Stress

= jiang et al., 2016

GR ±

Melatonin function in plant growth and physiology

MEL regulate different metabolic processes in plants and animals. Shape of MEL molecules is endogenous in all plant species. In plant organs attentiveness of MEL are varies in different tissues (Reiter et al., 2015). Melatonin are structural biogenic indole-amine tryptophan, tryptamine, and serotonin) and also linked to indole-3acetic-acid (IAA) as well as indole compounds, which are very imperative in physiology of plant (common auxin. Metabolic ways of tryptophan in mammals and plants) as deliberate by (Murch et al., 2000) and are shown in Figure 1. Melatonin are present in various plants seeds, roots, leaves, fruits, Table 3, shows the presence of melatonin in various plants. MEL work as auxin to promote plant vegetative growth in many plant species (Paredes et al., 2009). (Murch et al. 1997) disclosed that MEL concentration improve root growth in Hypericum perforatum L plant, as compared to the use of auxin, serotonin.

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Figure 1. Metabolic pathways of tryptophan in mammals and plants as proposed by (Murch et al.

200)

In metabolic processes MEL plays an important role and normalize Proline (Antoniou et al., 2017). MEL keeps plant chlorophyll and membrane integrity by donating plant water balance and root formation (Wang et al., 2013; Wei et al., 2014; Arnao and Hernandez 2009; Chen et al., 2009). MEL work as scavenging agent for ROS, auxins as plant growth promotor and signal molecules Paredes et al., 2009. MEL turns in numerous plant biological, metabolic, rooting, catabolism of chlorophyll, and stress tolerance (Park and back. 2012; Arnao and Hernandez 2009; Liang et al., 2015; Zhang et al., 2017). MEL synthesized by plants and perform as antioxidant or a modulator of plant growth and improvement in plants (Fleta et al., 2005).

Soybean coating with melatonin also enhanced plant growth and yield (wei et al., 2014). Similar to the effect of IAA, melatonin affects formation of lateral roots, increases root and shoot biomass in lupin (Arnao and Hernandez 2007. Melatonin also germination rate under adverse condition, and refine plant production quality (Arnao et al., 2014; Tan et al., 2012). Exogenous melatonin lower concentrations raised the content of endogenous IAA in plant roots, however melatonin concentration higher levels had no effect on IAA content (Chen et al., 2009).

Melatonin work as scavenger and antioxidant to detoxify the OH−, H2O2, Nitric oxide, ONOO−, HNO3, and HClO, which are biosynthesized under stress environments. Furthermore, treatment with melatonin promote antioxidant enzyme events under abiotic stress circumstances. About 10 free radicals hunt by one molecule of melatonin (Tan et al., 2007). Nitrogen and carbohydrate metabolism could be improved with melatonin treatment, it also has good impact on readjustment of transcription (Shi et al., 2015). Signal transduction is affected by MEL

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application; it also plays main role to regulate plant bio-physical practices. The use of MEL is therefore, recommended.

Table3. Reported Melatonin in some edible Plants.

Crop Used

Methodology

Melatonin Content(pg/g FW(DW) Tissue

References

Apple GC-MS 0.16 Badria 2002

Aspargus RIA 9.5 Hattori et al., 1995

Barley LC 500-12000 R;82,300S Hernandez et al., 2005;

Arnao and Hernandez 2009

Cucumber fruit seed

RIA 24.6, 11,000 Hattori et al., 1995;

Posmyke et al., 2009 chilies UHPLC-

MS/MS

31-93 Riga et al., 2014

Kiwi RIA 0.02 Hattori et al., 1995

Kidney bean

ELISA 529DW Aguilera et al., 2016

Rice HPLC 100L; 500S; 200R; 400F1 Park and back 2012;

Park et al., 2013

Sunflower HPLC 29,000DW Manchester et al., 2000

Tea HOLC 2.12µgg^-1 Chen et al., 2003

Tomato LC 15,000 – 142000L Arnao and Hernandez

et al., 2013

Wheat LC 124,700S Hernandez 2005

Abbreviation; L, stands for leaf, R, stand for root, FL, stands for flower, GC-MS, stands for gas chromatographic-mass spectroscopy, RIA stands for radioimmunoassay, LC, stands for liquid chromatography, UHPLC-MS/MS, stands for ultra-high performance liquid chromatography coupled to mass spectrometry in tandem mode, ELISA, stands for enzyme linked immunosorbent assay, HPLC, stands for High performance liquid chromatography.

Melatonin function in mitigating abiotic stresses i) Melatonin function under Drought Condition.

Water shortage is one of the main issue throughout the world and more than 100 countries worldwide face water deficit problem. It has been estimated that about two thirds population of the world population will face water deficit by 2025 (Zhang et al., 2017). Research work shows that drought problem will increase in coming years which will not only creative problem for human being but will also effect s agriculture productivity severely (Kijne 2006). Research indicates that due to climatic change and increase in arid and semi-arid zones in the world leads to increase drought, soil erosion, and salinization. (turkes and Artan 1994). Drought also effect plant traits, productivity, defensive system and photosynthetic activities (Farooq et al., 2009;

Bajaj et al., 1999; Arora et al., 2002; Escuredo et al., 1998). Drought restricts plants photochemical movement and declines enzymes activities in Calvin circle (Monakhova and Chernyadev 2002). Research indicates that plant treated with melatonin under drought condition, improve plant antioxidant (Li et al., 2016). Brassica napus L treated with MEL 0.05 mmol/L

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reduced the toxic effect of drought on plant growth. Moreover, MEL treatment reduced hydrogen peroxide (H2O2) and augmented plant antioxidant activity and osmotic solutes (Li et al., 2018).

Application of endogenous MEL also improve plant photosynthetic ability and stress related phyto-hormones under drought conditions. (Fleta-Soriano et al.,2005) exposed that MEL treatment improved photosystem II resulting in a protective factor in maize crop under drought.

MEL treatment improve Fv/Fm ratio in plant, which reinstate plant after drought effect. (Gui et al., 2017) investigate that wheat effected by drought reinstated with melatonin treatment. MEL improved wheat antioxidant, reactive oxygen species scavenging behavior and reduced demages in membrane. MEL also caused a thicker epidermal cell, intact grana lamella of chloroplast and leaf structure, and greater photosynthetic act. They revealed that wheat treated with MEL improved genes expression and enzymes activities. Likewise, (Wang et al. 2013; Meng et al., 2014) pointed out that melatonin treatment reduces drought created toxic effect, improves photosynthesis activities and uplift antioxidant enzymes behavior and limit ROS harmfully effect. (Ma et al.,2018) pointed out that melatonin treatment increased ME bio-synthesis genes expression in Agrostis stolonifera. Melatonin application reduce synthetic gene expression of ABA (MdNCED3) and raise catabolic genes expression like MdCYP707A1 and MdCYP707A2 (Li et al., 2015). Melatonin application reduce the level of H2O2 and aminocyclopropane-1- carboxylic acid (ACC) creation, raise indole acetic acid (IAA) and zeatin due to which water use efficiency and ability of photosynthetic increase (Li et al., 2017). Drought also reduce the production of abscisic acid (ABA), which cause stomata closer (Seki et al., 2007). Use of MEL is useful to reinstate the plant after drought has happened and plants are re-watered (Meng et al.

2014; Seki et al. 2007; Wang et al. 2014).

ii) Melatonin and Heavy metal stress.

Heavy metals presence in soil prevents growth rate and cause plant death. (Prasad 1995; Salt 2001). Up to certain amount plant related metal are required However, in plant root some metal presence has harmful on the plants. Some metals (Cd, Cr, Zn, Cu, Pb, Ni), have harmfully effect on plant growth and yield (Prasad & Strazalka 2002). Theses metals collect in plants system and break plant growth and plant nutrient promise (Brune et al. 1995). Due the entrance of these metals, uptake capacity of plants for essential minerals damaged by producing a poisonous effect and by substituting the like iron for the plants. Plant photosynthesis rate also effected by heavy metals, by stimulating ROS in plants. Presence of metal presence in plant caused raised in ethylene which limit the plant growth, CO2 fixation and compact sugar pathway (Buchanan et al., 2000). The presence of metals in plant support ROS, which cause plants oxidative stress (Loureiro et al., 2006; Hu et al., 2007; Gupta et al., 2009). The exposer of plants to metals like (Pb, zn, Cd, etc.) have been shown to persuade melatonin bio-synthesis for refining effects of metal stress (Tal et al., 2011). (Tan et al., 2007) examine that melatonin treatment raised pea ability of phytoremediation under copper stress. Several work revealed that treatment with exogenous MEL compact the toxicity of heavy metals such as cadmium (Cd), copper (Cu), nickel (Ni) etc. (Posmyk et al., 2008; Nawaz et al., 2018). (Tang et al.2015) investigated that as foliar melatonin concentration 150 μmol·L⁻¹ was best for eggplant under cadmium stress. They further revealed that melatonin application improved photosynthesis activities in eggplant under Cd stress. MEL treatment increase removal rate of cadmium and cadmium transfer from cytosol to the vacuole and cell wall (Hasan et al., 2015). (Gu et al..2017) pointed out that cadmium stress condition in alfalfa improved by endogenous MEL treatment and correct expression of ion channel genes in plant against cadmium stress. They revealed that MEL treatment re-establishing micro RNA redox hormones in plant by decreasing toxic effect of cadmium (Cd). Additionally,

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(Safari et al.,2017) showed that presence of boron (B) in excess amount restrict pepper dry mass and also decrease photosynthesis rate. However, they pointed out that MEL treatment of 1 μM, increase photosynthesis rate, nutrient up taking capacity, antioxidant and sugar accumulation and reduced ROS in plant. (Zhang et al.,2017) verified that application of exogenous melatonin in Glycine max could improve aluminum prompted phyto toxicity. Although melatonin treatment with 0.1mM and 1 mM improved root growth and reduced H₂O₂. MEL root application at rate of 1 mM increased plant antioxidant activity under stress (A1). (Ni et al.,2018) showed that melatonin treatment reduced cadmium (Cd) toxic effect in wheat and improved plant APX and SOD activities. They concluded that MEL reduced the effect of ROS by improving plant antioxidant pigment. (Moussa and Algamal 2017) investigated that application of MEL in spinach enhancing plant antioxidant character and reducing level of ROS.

iii) Melatonin and Salinity Stress.

Extreme salinity in soil severely reduce crop yield throughout the world. Salinity affects about 110 million hectors land (arid and semi arid) areas of the world. According to foods and agriculture organization (FAO) report, 20 to 30 million hectors areas is badly damage due to extreme salt presence (shi et al., 2015). Salt accumulation in soil is due to natural phenomena as well as due increased in water table (Leyva et al., 2011). Due to over population and misuse of water clean water availability for agriculture practice becoming inadequate, so treated and untreated water introduced for agricultural activities which cause salt accumulation in soil. Salt presence in soil create osmotic stress in plants by water potential sinking and raising the energy required for the water and nutrient intake. Ionic stress in plant tissues taking place due to accumulation of chlorine (Cl), and Sodium (Na) ions (Munns and tester 2008; Flowers et al., 2010; Yildirim et al., 2006). It has been reported that disturbance in plant morphological and physiological behavior and growth restriction is due to the presence of salt (NaCl) in soil or in water (Cirillo et al., 2015). Plant nutrients variation and shortage also cause by salinity (Parida and Das 2005). Plant oxidative stress and ROS formation promoted by salts (Gao et al., 2008), which create significant membranes damage and other cellular structures (Arora et al., 2008).

Presence of salt affect plant growth related traits as well as plant chemical traits, which leads to low quality yield and yield loss (Yu et al., 2018). MEL application improved plant salt resistance by either use MEL as exogenous or by enzymes genetic reform intricate in synthesis of melatonin (Kanwar et al., 2018). Use of MEL improved growth parameters, antioxidant enzymes, chlorophyll content and decrease the level of ROS and oxidative stress in cucumber grown under salinity condition (Wang et al., 2016). (Dawood et al.,2015) revealed that MEL application in fava bean (grown under salt stress environment) reduced the harmful effect of salts (Na, Cl), improved water related traits, plant chemical pigments, biomass, phenolic matter, and plant nutrient uptake capacity. Melatonin concentration of 500 mM was more operative than that of 100 mM concentration. (Zhou et al., 2016) studied the impacts of MEL conducts on tomato photosynthetic activity in salty environments. They concluded that melatonin treatment reduced the toxic effect of salt on plant growth parameters and photosynthesis process. MEL application recover electron transport chain of protein biosynthesis photosynthetic. MEL application reduced the ROS levels. Likewise, watermelon roots treated with MEL reduced salt-stress harmfully effect in photosynthetic capacity reduced oxidative stress, improved plant antioxidant behavior and redox homeostasis (Li et al., 2017). Melatonin treatment increased salt tolerance and K⁺ /Na⁺ in potato, decreasing sodium chloride (NaCl) absorption and swelling K⁺ (Yu et al., 2018). MEL treatment enhance nutrient up taking capacity, seedling growth, and nitrogen metabolism detection in Cucumis sativus, grown under salty environment (Zhang et al., 2017). (Ke

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et al.,2018) Investigate that MEL treatment with 10–500 μM could improve germination and seed growth rate in rice grown under salty condition. they further concluded that MEL treatment reduced the harmfully effect of salt stress in wheat by promoting poly-amine metabolism, improving antioxidant and ROS scavenging behavior This perfection was documented to dipping sodium (Na⁺) and chloride (Cl⁻) ions content in leaves and roots (Li et al., 2017). (Jiang et al.

2016) revealed that exogenous MEL application on maize sown in salt effected environment, produced good impact on growth parameters, photosynthesis processes, antioxidant activities, and. It was established that melatonin concentration in roots raised because of stress environments, swelling to 6 times the melatonin levels likened to the control. This increase can show a major part in the enhancement of stress environments (Arnao and harnandez 2009).

Treatment with exogenous MEL exhibited a melatonin main effect linked to lipid metabolism with K⁺ / Na⁺ homeostasis in potato which grown in salt effected environment (Yu et al., 2018).

Root MEL application improved antioxidant role in watermelon and reduced the toxic behavior of salt on photosynthetic activity by controlling oxidative stress. This effect regulates stomatal function and hence improved transport of electrons in photo system II (Li et al., 2018). (Liang et al.,2015) use melatonin for treatment of rice grown in salt effected area and determined that application of melatonin control damage in chlorophyll and senescence genes transcripts, therefore refining salt tolerance in plant. They also noted that use of melatonin protects leaf senescence and cells from death caused by ROS.

vi) Melatonin under Cold and Hot Environment.

temperature is essential for plants every stage of growth, and this requisite may differ between plant varieties and species. Variation in temperature from optimum requirement of plant effect plant germination, growth rate and yield and also result into various plant diseases (Pierce 1987).

Species of hot climatic environment are sensitive to low temperatures (Decoteau 2000). Research work revealed that low temperature effect plant cells metabolic system and cause water stress, also damages cell membranes, sugars, phenolic, phospholipids, protein, and ATP (Kratsch &

wise 2000; Lyons 1973). Cold environment result into extreme production of reactive oxygen species (O2 -, H2O2, OH-) in plant cells. Reactive oxygen species may cause lipid peroxidation and oxidative alterations in proteins and nucleic acids (Liu et al., 2010; Fan et al., 2014).

However, the plants have developed a defensive system and non-enzymatic acetyl-salicylic-acid and gluta-thione (GSH) to improve and overhaul damage produced due to oxidative stress (Almeselmani et al., 2006; Yin and Chen 2008). Low temperature tolerance in plants related to stimulation of ROS scrubbing systems. Plants that grown in cooled climate harmfully effected by high temperature. High temperature damagingly affect plant germination development period, declines photosynthetic ability, assimilation of carbon dioxide (CO2), and plant metabolic practices (Alkhetab and Paulsen 1999; Sam et al., 2000). High temperatures also cause into weaken constancy of membrane, resultant in necrotic spots same indication like water stress in leaves and hence causing to deaths (Hall 2001). Plants food intakes also affected by high temperature stress (Rosa et al., 2003). Increase in temperature also had bad impact on plant. High temperature create oxidative stress which cause yield reduction, damage in membrane, degrade proteins and slow down plants pigments, and deprivation of DNA elements in plants (Suzuki and Mittler 2006). Many researchers investigated that use of melatonin as exogenous defend plants from harmful effect of excesses temperature. (Tan et al., 2000). Research work also investigated that MEL antioxidant capacity could reinforce plants exposed heat and cold stresses (Arnao and Hernandez 2018; Janas and Posmyke 2013). Several studies revealed that biosynthesis of MEL and upregulated genes induced by MEL supplementation under low temperature stress

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conditions (Bajwa et al. 2014; Shi & Chen 2014). The harmful effect of low and high temperature on plants by down or upregulating genes and proteins, polyamine metabolism modulating, removal of ROS, chlorophyll-a, b and heat shock protein synthesis been improved with MEL treatment (Tan et al., 2007, Shi and Chen 2014; Turk et al., 2014; Xu et al., 2016;

Zhang et al., 2017). (Balabusta et al. 2016,) showed that cucumber seeds treated with melatonin had improved SOD activities and reduce ROS under chilling stress. Research conducted on tomato under chilling stress also indicates that MEL treatment compact photo inhibition by improving non-photochemical reducing through introduction of violaxanthin de-epoxidase activity (Ding et al., 2017). (Alam et al.,2018) determined that tall fescue plant with melatonin treatment under high temperature stress had higher value of proteins, chlorophyll, and antioxidants activities, while lower malondial-dehyde and ROS, as compared to non-treated plants. Their result also revealed that plants thermos-tolerance improved with MEL treatment.

another research work indicates that, maize seeds priming under chilling stress with MEL (50 and 500 μM) regulated melatonin-associated visible proteins in seeds to low temperature and improved tolerance in plant to chilling (kolodziejczyl et al., 2016). Lolium perenne plants treated with MEL as foliar application, result into higher chlorophyll content, photo synthesis capacity and biomass as compared to non-treated lolium perenne under heat stress. Plants treatment endogenous melatonin and condensed ABA content and downregulate genes related to ABA (Zhang et al., 2017). Under chilling condition MEL applications improved antioxidant enzymes superoxide dismutases (SOD) and catalase (CAT), but compact hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) content of pepper seedlings. Lipid peroxide decreasing in tissues result to promote antioxidant activities in plant., therefore pepper seed emergence and germination rate increased. (Korkamaz et al., 2017). (Xu et al.,2010) also investigate that treatment with MEL significantly increase antioxidants superoxide dismutases (SOD), catalase (CAT), ascorbate peroxidase (APX), peroxidase (POD), and Ascorbic acid (AA), vitamin E (non-enzymatic antioxidant), reduced reactive oxygen species (ROS) levels and lipid per-oxidation in cucumber under stress created by higher temperature. (Posmyk et al.,2009) examined that melatonin osmo and hydro priming application on germination in cucumber to increase rate of germination under low temperature creative stress. They revealed that cucumber seed germination amplified to 50%–60% at 15°C and further additional MEL 25 μM to 100 μM amplified the germination ratio of cucumber seeds. From this result they reported that application of MEL protected cell membranes beside peroxidation in cucumber seeds during chilling stress but increase in melatonin level is responsible for oxidative changes in proteins.

v). Melatonin role in Oxidative Stress.

As an antioxidant and signaling molecule MEL develop strong reaction to plant stress, particularly abiotic stresses. MEL along with other plant hormones control the effect of drought.

In plants cell membranes permeability change by MEL, facilitated by ion transporters, which control plant stomata closing and opening during transpiration. Therefore, MEL antioxidant behavior make it effort as an endogenous plant bio‐stimulator for biotic and abiotic stresses (Amao & Hernandez 2019). Melatonin also increase plant tolerance against heavy metals like zinc, cadmium, copper and vanadium. vanadium, is present in the Earth’s crust. Watermelon have been investigated to check its response against vanadium as well as the effect of MEL on vanadium. Watermelon seeds were exposed to vanadium and treated with 50mg/L MEL. Result indicated that MEL treated seeds appeared with improved chlorophyll content and photosynthetic response of plant as compared to the non‐melatonin‐treated plants. MEL reduce transcript level of senescence-associated-genes (SAG) and the effect of pheide-a-oxygenase

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(PAO). MEL also boost SOD and CAT antioxidant enzymes activities and reduce the vanadium presence in plant and hence decrease plant stress and improve plant growth (Nawaz et al., 2018).

Iron level variation in plant reduce plant growth rate, secondary plant metabolic behavior and antioxidant enzymes activities. To overcome on these deficiencies MEL is used to change the genes expression and properly maintain iron level in plant. Plants antioxidant reduction related to flavonoids and phenolic. After melatonin treatment, plant antioxidant (ferric-reducing) activities increase SAR stressed, which also contains their antioxidant assets. MEL treatment also reduce lipid peroxide and hydrogen peroxide level inn plants, which decrease plant stress and finally improve photosynthesis and plant growth. Crop yield also effect with acid rain, which could be treated with MEL application (debnath et al., 2018). Plant defense system and antioxidant behavior could be improved with MEL treatment. Carya cathayensis Chinese hickory plant which is available on commercial base and known throughout due to its nuts. But this plant took more time to reach nut growing stage. This plant very sensitive to stresses (biotic and abiotic). In order to reduce Carya cathayensis plant, vegetative and reproductive phase grafting can be done.

Therefore, MEL is used in the grafting of Carya cathayensis under drought stress, which enhanced efficiency of plant defense system and improve photosynthesis activities and reduce the effect of ROS and activating Proline content. This indicates that MEL treatment regulates biological routes at catalytic and molecular levels (sharma et al., 2020). Melatonin plays an important role against abiotic and biotic stresses, it is used to boost up plants defense mechanism against oxidative stress, some of which are discussed below in Table 4. While, Fig 2 indicates a diagrammatic sketch of melatonin defense system.

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Table 4. Protective role of melatonin in various crops against different abiotic stresses.

crop Stress condition Concentration Function References

Arabidopsis Heat 1000µM Improved seed germination under heat stress

Harnandez et al., 2015 Apple Drought 100 µM Reduced ABA activity and

radical scavenging

Li et al., 2014 Apple waterlogging 200 µM Reduced chlorosis and

wilting of the seedlings

Zheng et al., 2017

Barley senescence 1 µM Boosted chlorophyll

content

Arnao and Harnandez 2009 Brassica napus

L.

Drought 0.05 mmol/L Increased the overall growth indices of brassica seedlings

Li et al., 2018 Bermuda grass Cold 100 µM Induced photosynthetic

activity under cold stress

Hu et al., 2018

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Cucumber salinity 100 µM Overall growth Wang et

al., 2016 Cucumber Cinnamic acid 10 µM Rescued cucumber

seedlings from Cinnamic acid stress and increased the allocation of dry weight in roots.

Li et al., 2017

Eggplant Cadmium stress 150 µmol/L Enriched photosynthetic activity

Tang et al., 2015 Faba bean salinity 500 µM Enriched photosynthetic

activity and mineral accumulation

Dawood and Elawdi 2015 Graps Water deficient 200 µmol/L Amended antioxidative

enzymes activity

Meng et al., 2014 Maize Drought 100 µmol/L Photosynthesis and growth Ye et al.,

2016

Melon Cold 200 µM Improved proline and

ascorbic acid content

Zhang et al., 2017 Medicago

sativa

Drought 10 µM regulation of nitro-

oxidative and

osmoprotective homeostasis

Antoniou et al., 2017 Malus

hupehensis

salinity 0.1mM Improved photosynthetic activity and better plant growth

Li et al., 2012 Malus

hupehensis

Alkaline 5 µM Significantly induced the tolerance against alkaline stress by increasing the antioxidant activity and biosynthesis of polyamines

Gong et al., 2017

Perennial ryegrass

High

Temperature

20 µM Regulate abscisic acid and cytokinin biosynthesis

Zhang et al., 2017 Potato Salinity 100 µM Better chlorophyll content,

antioxidant activities and water content

Yu et al., 2018 Pisum sativum

L.

Oxidative stress 50 µM Reduced O2 •−

accumulation in leaf tissues and preservation of photosynthetic pigments

Szafra et al., 2016

Rice Salinity 20 µM Delay leaf senescence and cell death in rice

Liang et al., 2015 Red cabbage Heavy metal 10 µM improved seed germination

and reduced the toxic effect of metal on the

Posmyk et al., 2008

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seedling.

Soybean Multiple stress 100 µM Boost and maintain the overall plant growth

Wei et al., 2014 Soybean Aluminum

stress

50 µM Enhanced root growth and reduced aluminum toxicity

Zhang et al., 2017 Sunflower salt 15 µM Regulate root growth and

hypocotyl elongation under salt stress

Mukherjee et al., 2014

Tomato Cold and

salinity

100 µM Improved photosynthesis and regulation of photosynthetic electron transport

Yang et al., 2018;

Zhou et al., 2016

Tomato Heat and

salinity

100 µM Induced antioxidant enzymes activity and better photosynthetic

performance

Martinez et al., 2018 Tomato Acid rain 100 µM Enhanced tolerance against

simulated acid rain and

increased the

photosynthetic activity

Debnath et al., 2018

Tea Cold 100 µM Triggered photosynthetic

and antioxidant enzymes activities

Li et al., 2018 watermelon Salinity 150 µM Redox homeostasis and

improved photosynthetic activity

Li et al., 2017 Watermelon Vanadium stress 0.1 µM Lower the concentration of

vanadium in leaf, stem and better photosynthetic and antioxidants activity

Nawaz et al., 2018

watermelon Cold 150 µM and 1.5 µM

Alleviate cold stress by inducing long-distance signaling in the untreated tissue.

Li et al., 2017

Wheat Drought and

nano-ZnO

500 µM and 1nM

Augmented seedling percentage, growth, and antioxidant enzymes activities.

Cui et al., 2017;

wheat Cadmium stress 50mM Reduce the level of hydrogen peroxide which increases the wheat plants growth

Ni et al., 2018

Conclusion

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Grounded on literature information, Melatonin under abiotic stress environment could work as a regulator to improve plant yield. MEL also consider tolerance to stress. Melatonin improves plant growth parameters, plant anti-oxidants response, plant water related traits, and photosynthesis activities of plant and hence improve yield under opposed environment. These improvements in plants caused by

(i) refining plant photosynthetic capability.

(ii) scavenging ROS.

(iii) augmenting plant anti-oxidant capability.

(iv) stress linked genes regulation, and (v) enrichment of osmotic metabolites.

There are as yet numerous unanswered inquiries regarding MEL and more areas for additional exploration. The systems by which MEL is delivered are still generally uncertain and should be explained by various plant cells in various circumstances.

References;

 Acosta-Motos JR, Ortuño MF, Bernal-Vicente A, Diaz-Vivancos P, Sanchez-Blanco MJ, Hernandez JA. Plant responses to salt stress: Adaptive mechanisms. Agronomy. 2017; 7:18.

DOI: 10.3390/agronomy7010018

 Ahammed, G.J.; Wu, M.; Wang, Y.; Yan, Y.; Mao, Q.; Ren, J.; Ma, R.; Liu, A.; Chen, S.

Melatonin alleviates iron stress by improving iron homeostasis, antioxidant defense and secondary metabolism in cucumber. Sci. Hortic. 2020, 265, 109205.

 Alam MN, Zhang L, Yang L, Islam R, Liu Y, Luo H, et al. Transcriptomic profiling of tall fescue in response to heat stress and improved thermotolerance by melatonin and 24- epibrassinolide. BMC Genomics. 2018; 19:224. DOI: 10.1186/s12864-018-4588-y

 Alam, M.N.; Wang, Y.; Chan, Z. Physiological and biochemical analyses reveal drought tolerance incool-season tall fescue (Festuca arundinacea) turf grass with the application of melatonin. Crop Pasture Sci.2018, 69, 1041–1049. (CrossRef)

 Al-Khatib K, Paulsen GM. High temperature effects on photosynthetic processes in temperate and tropical cereals. Crop Science. 1999; 39:119-125

 Almeselmani M, Deshmukh PS, Sairam RK, Kushwaha SR, Singh TP. Protective role of antioxidant enzymes under high temperature stress. Plant Science. 2006; 171:382-388

 Antoniou C, Chatzimichail G, Xenofontos R, Pavlou G, Panagiotou E, Christou A, et al.

Melatonin systemically ameliorates drought stress-induced damage in Medicago sativa plants by modulating nitro-oxidative homeostasis and proline metabolism. Journal of Pineal Research. 2017;62: e12401. DOI: 10.1111/jpi.12401

 Antoniou, C.; Chatzimichail, G.; Xenofontos, R.; Pavlou, J.J.; Panagiotou, E.; Christou, A.;

Fotopoulos, V. Melatonin systemically ameliorates drought stress-induced damage in Medicago sativa plants by modulating nitro-oxidative homeostasis and proline metabolism. J.

Pineal Res. 2017, 62, e12401. (CrossRef) (PubMed)

 Arnao MB, Hernandez-Ruiz J. Melatonin in plants. Plant Signaling & Behavior.

2007;2(5):381-382

 Arnao MB, Hernández-Ruiz J. Chemical stress by different agents affects the melatonin content of barley roots. Journal of Pineal Research. 2009;46:295-299. DOI: 10.1111/j.1600- 079X.2008. 00660.x

(17)

 Arnao MB, Hernandez-Ruiz J. Melatonin and its relationship to plant hormones. Annals of Botany. 2018; 121:195-207. DOI: 10.1093/aob/mcx114.

 Arnao MB, Hernández-Ruiz J. The physiological function of melatonin in plants. Plant Signaling & Behavior. 2006; 1:89-95. DOI: 10.4161/psb.1.3.2640

 Arnao, M.; Hernández-Ruiz, J. Protective effect of melatonin against chlorophyll degradation during the senescence of barley leaves. J. Pineal Res. 2009, 46, 58–63.

(CrossRef) (PubMed)

 Arnao, M.B.; Hernández‐Ruiz, J. Melatonin: A new plant hormone and/or a plant master regulator? Trends Plant Sci. 2019, 24,38–48.

 Arora A, Sairam RK, Srivastava GC. Oxidative stress and antioxidative systems in plants.

Current Science. 2002; 82:1227-1238

 Arora N, Bhardwaj R, Sharma P, Arora HK. Effects of 28-homobrassinolide on growth, lipid peroxidation and antioxidative enzyme activities in seedlings of Zea mays L. under salinity stress. Acta Physiologiae Plantarum. 2008; 30:833-839.

 Bajaj S, Jayaprakash T, Li L, Ho TH, Wu R. Transgenic approaches to increase dehydration- stress tolerance in plants. Molecular Breeding. 1999; 5:493-503

 Bajwa VS, Shukla MR, Sherif SM, Murch SJ, Saxena P. Role of melatonin in alleviating cold stress in Arabidopsis thaliana. Journal of Pineal Research. 2014; 56:238-245. DOI:

10.1111/jpi.12115

 Bałabusta M, Szafranska K, Posmyk MM. Exogenous melatonin improves antioxidant defense in cucumber seeds (Cucumis sativus L.) germinated under chilling stress. Frontiers in Plant Science. 2016; 7:575. DOI: 10.3389/fpls.2016.00575

 Boyer JS. Plant productivity and environment potential for increasing crop plant productivity, genotypic selection. Science. 1982; 218:443-448.

 Brune A, Urbach W, Dietz KJ. Differential toxicity of heavy metals is partly related to a loss of preferential extraplasmic compartmentation: A comparison of Cd-, Mo-, Ni-, and Zn- stress. New Phytologist. 1995; 129:404-409

 Buchanan BB, Gruissen W, Jones RL. Biochemistry and Molecular Biology of Plants.

Rockville: American Society of Plant Physiology; 2000. pp. 1-367

 Campos, C.N.; Ávila, R.G.; de Souza, K.R.D.; Azevedo, L.M.; Alves, J.D. Melatonin reduces oxidative stressand promotes drought tolerance in young Coffea arabica L. plants.

Agric. Water Manag. 2019, 211, 37–47. (CrossRef)

 Chen Q, Qi W, Reiter RJ, Wei W, Wang B. Exogenously applied melatonin stimulates rootgrowth and raises endogenous indole acetic acid inroots of etiolated seedlings of Brassica juncea. Journal of Plant Physiology. 2009; 166:324-328. DOI: 10.1016/j.jplph.2008.06

 Chen, Y.E.; Mao, J.J.; Sun, L.Q.; Huang, B.; Ding, C.B.; Gu, Y.; Liao, J.Q.; Hu, C.; Zhang, Z.W.; Yuan, S. Exogenous melatonin enhances salt stress tolerance in maize seedlings by improving antioxidant and photosynthetic capacity. Physiol. Plant. 2018, 164, 349–363.

(CrossRef) (PubMed)

 Cirillo C, Rouphael Y, Caputo R, Raimondi G, Sifola MI, De Pascale S. Effects of high salinity and the exogenous application of an osmolyte on growth, photosynthesis, and mineral composition in two ornamental shrubs. The Journal of Horticultural Science and Biotechnology. 016; 91:14-22. DOI: 10.1080/14620316.2015.1110988

(18)

 Cui G, Zhao X, Liu S, Sun F, Zhang C, Xi Y. Beneficial effects of melatonin in overcoming drought stress in wheat seedlings. Plant Physiology and Biochemistry. 2017; 118:138-149.

DOI: 10.1016/j.plaphy.2017.06.014

 Das, K.; Roy Choudhury, A. Reactive oxygen species (ROS) and response of antioxidants as ROS-scavengers during environmental stress in plants. Front. Environ. Sci. 2014, 2, 53.

(CrossRef)

 Dawood MG, EL-Awadi ME. Alleviation of salinity stress on Vicia faba L. plants via seed priming with melatonin. Acta Biológica Colombiana. 2015;20(2):223-235. DOI:

10.15446/abc.v20n2.43291

 Debnath, B.; Hussain, M.; Irshad, M.; Mitra, S.; Li, M.; Liu, S.; Qiu, D. Exogenous melatonin mitigates acid rain stress to tomato plants through modulation of leaf ultrastructure, photosynthesis and antioxidant potential. Molecules 2018, 23, 388. (CrossRef) (PubMed)

 Debnath, B.; Islam, W.; Li, M.; Sun, Y.; Lu, X.; Mitra, S.; Hussain, M.; Liu, S.; Qiu, D.

Melatonin mediates enhancement of stress tolerance in plants. Int. J. Mol. Sci. 2019, 20, 1040. (CrossRef)

 Decoteau DR. Vegetable Crops. New Jersey, USA: Prentice-Hall Inc.; 2000

 Denby K, Gehring C. Engineering drought and salinity tolerance in plants: Lessons from genome-wide xpression profiling in Arabidopsis. Trends in Biotechnology. 2005;23(11):547- 552. DOI: 10.1016/j.tibtech.2005.09.001.

 Ding F, Wang M, Liu B, Zhang S. Exogenous melatonin mitigates photo inhibition by accelerating nonphotochemical quenching in tomato seedlings exposed to moderate light during chilling. Frontiers in Plant Science. 2017; 8:244. DOI: 10.3389/fpls.2017.00244

 Dubbels R, Reiter RJ, Klenke E, Goebel A, Schnakenberg E, Ehlers C. Melatonin in edible plants identified by radioimmunoassay and by high performance liquid chromatography mass spectrometry. Journal of Pineal Research. 1995; 18:28-31. DOI: 10.1111/j.1600- 079X.1995.tb00136.x

 Erland LA, Murch SJ, Reiter RJ, Saxena PK. A new balancing act: The many roles of melatonin and serotonin in plant growth and development. Plant Signaling & Behavior.

2015;10: e1096469. DOI: 1080/15592324.2015.1096469

 Escuredo IP, Arrese-Igor C, Becana M. Oxidative damage in pea plants exposed to water deficit or paraquat. Plant Physiology. 1998; 116:173-181

 Esim N, Atici O. Nitric oxide improves chilling tolerance of maize by affecting apoplastic antioxidative enzymes in leaves. Plant Growth Regulation. 2014; 72:29-38. DOI:

10.1007/s10725-013-9833-4

 Fan J, Ren J, Zhu W, Amombo E, Fu J, Chen L. Antioxidant responses and gene expression in bermudagrass under cold stress. Journal of the American Society for Horticultural Science.

2014; 139:699-705

 FAO. Properties and Management of Dry Lands. Rome, Italy: Food and Agriculture Organization; 2005(55) Kijne JW. Abiotic stress and water scarcity: Identifying and resolving conflicts from plant level to global level. Field Crops Research. 2006; 97:3-18

 Farooq M, Wahid A, Kobayashi N, Fujita D, Basra SMA. Plant drought stress: Effects, mechanisms and management. Agronomy for Sustainable Development. 2009; 29:185-212

 Fleta-Soriano E, Diaz L, Bonet E, Munne-Bosch S. Melatonin may exert a protective role against drought stressin maize. Journal of Agronomy and Crop Science. 2017; 203:286-294.

(19)

DOI: 10.1111/jac.12201(26) Hernandez-Ruiz J, Cano A, Arnao MB. Melatonin acts as a growth stimulating compound in some monocot species. Journal of Pineal Research. 2005;

39:137-142. DOI: 10.1111/j.1600-079X.2005. 00226.x

 Flowers T, Galal H, Bromham L. Evolution of halophytes: Multiple origins of salt tolerance in land plants. Functional Plant Biology. 2010; 37:604-612

 Gao S, Ouyang C, Wang S, Xu Y, Tang L, Chen F. Effects of salt stress on growth, antioxidant enzyme and phenylalanine ammonia-lyase activities in Jatropha curcas L seedlings. Plant, Soil and Environment. 2008; 54:374-381

 Gao, W.; Feng, Z.; Bai, Q.; He, J.; Wang, Y. Melatonin-mediated regulation of growth and antioxidant capacity in salt-tolerant naked oat under salt stress. Int. J. Mol. Sci. 2019, 20, 1176. (CrossRef) (PubMed)

 Gong, X.; Shi, S.; Dou, F.; Song, Y.; Ma, F. Exogenous melatonin alleviates alkaline stress in Malus hupehensis Rehd. by regulating the biosynthesis of polyamines. Molecules 2017, 22, 1542. (CrossRef)

 Gu Q, Chen Z, Yu X, Cui W, Pan J, Zhao G, et al. Melatonin confers plant tolerance against cadmium stress via the decrease of cadmium accumulation and reestablishment of microRNAmediated redox homeostasis. Plant Science. 2017; 261:28-37. DOI:

10.1016/j.plantsci.2017.05.001

 Gupta M, Sharma P, Sarin NB, Sinha AK. Differential response of arsenic stress in two varieties of Brassica junce a L. Chemosphere. 2009; 74:1201-1208

 Gürel A, Avcıoğlu R. Bitkilerde strese dayanıklılık fizyolojisi. In: Özcan S, Gürel E, Babaoğlu M, editors. Bitki Biyoteknolojisi II, Genetik Mühendisliği ve Uygulamaları, 21.

Bölüm. Konya: Selçuk University Foundation; 2001.pp. 308-313

 Hall AE. Breeding for heat tolerance. Plant Breeding Reviews. 1992; 10:129-168(104) Hall AE. Physiology and breeding for heat tolerance in cowpea, and comparison with other crops.

In: Kuo CG, editor. Adaptation of Food Crops to Temperature and Water Stress. Shanhua, Taiwan: Asian Vegetable Research and Development Center; 1993. pp. 271-284. Publ. No.

93-410

 Hall AE. Crop Responses to Environment. Boca Raton, Florida: CRC Press LLC; 2001

 Hardeland R. Melatonin in plants—Diversity of levels and multiplicity of functions.

Frontiers in Plant Science. 2016; 7:198. DOI: 10.3389/ fpls.2016.00198 (12) Arnao MB, Hernandez-Ruiz J. Melatonin: Plant growth regulator and/or bio stimulator during stress?

Trends in Plant Science. 2014; 19:789-797. DOI: 10.1016/j.tplants.2014.07.006.

 Hasan MK, Ahammed GJ, Yin L, Shi K, Xia X, Zhou Y, et al. Melatonin mitigates cadmium phytotoxicity through modulation of phytochelatins biosynthesis, vacuolar sequestration, and antioxidant potential in Solanum lycopersicum L. Frontiers in Plant Science. 2015; 6:601.

DOI: 10.3389/fpls.2015.00601.

 Hattori A, Migitaka H, Masayaki I, Itoh M, Yamamoto K, Ohtani-Kaneko R. Identification of melatonin in plant seed its effects on plasma melatonin levels and binding to melatonin receptors in vertebrates. Biochemistry and Molecular Biology International. 1995; 35:627- 634.

 Hernández, I.G.; Gomez, F.J.V.; Cerutti, S.; Arana, M.V.; Silva, M.F. Melatonin in Arabidopsis thaliana acts as plant growth regulator at low concentrations and preserves seed viability at high concentrations. Plant Physiol. Biochem. 2015, 94, 191–196. (CrossRef) (PubMed)

(20)

 Hernández-Ruiz, J.; Arnao, M.B. Relationship of melatonin and salicylic acid in biotic/abiotic plant stress responses. Agronomy 2018, 8, 33. (CrossRef)

 Hodžić, E.; Balaban, M.; Šuškalo, N.; Galijašević, S.; Hasanagić, D.; Kukavica, B.

Antioxidative response of Melissa officinalis L. and Valeriana officinalis L. leaves exposed to exogenous melatonin and excessive zinc and cadmium levels. J. Serb. Chem. Soc. 2019, 84, 11–25. (CrossRef)

 Hu K, Hu LY, Li YH, Zhang FQ, Zhang H. Protective roles of nitric oxide on germination and antioxidant metabolism in wheat seeds under copper stress. Plant Growth Regulation.

2007; 53:173-183

 Hu Z, Fan J, Xie Y, Amombo E, Liu A, Gitau MM, et al. Comparative photosynthetic and metabolic analyses reveal mechanism of improved cold stress tolerance in bermudagrass by exogenous melatonin. Plant Physiology and Biochemistry. 2016; 100:94e104. DOI:

10.1016/j.plaphy.2016.01.008.

 Hu, Z.; Fan, J.; Xie, Y.; Amombo, E.; Liu, A.; Gitau, M.M.; Khaldun, A.; Chen, L.; Fu, J.

Comparative photosynthetic and metabolic analyses reveal mechanism of improved cold stress tolerance in bermudagrass by exogenous melatonin. Plant Physiol. Biochem. 2016, 100, 94–104. (CrossRef) (PubMed)

 Huang, B.; Chen, Y.-E.; Zhao, Y.-Q.; Ding, C.-B.; Liao, J.-Q.; Hu, C.; Zhou, L.-J.; Zhang, Z.-W.; Yuan, S.; Yuan, M. Exogenous melatonin alleviates oxidative damages and protects photosystem II in maize seedlings under drought stress. Front. Plant Sci. 2019, 10, 677.

(CrossRef)

 Janas K, Posmyk M. Melatonin, an underestimated natural substance with great potential for agricultural application. Acta Physiologiae Plantarum. 2013; 35:3285-3292

 Jiang J, Cui Q, Feng K, Xu D, Li C, Zheng Q. Melatonin improves antioxidant capacity and ion homeostasis and enhances salt tolerance in maize seedlings. Acta Physiologiae Plantarum. 2016;38:82. 1-9. DOI: 10.1007/s11738-016-2101-2

 Kalefetoğlu T, Ekmekçi Y. The effects on drought on plants and tolerance mechanisms. Gazi University Journal of Science. 2005; 18:723-740.

 Kanwar MK, Yu J, Zhou J. Phytomelatonin: Recent advances and future prospects. J Pineal Res. 2018;65: e12526. https://doi.org/10.1111/jpi.12526.

 Ke Q, Ye J, Wang B, Ren J, Yin L, Deng X, et al. Melatonin mitigates salt stress in wheat seedlings by modulating polyamine metabolism. Frontiers in Plant Science. 2018; 9:1-11.

DOI: 10.3389/fpls.2018.00914(51) Li X, Yu B, Cui Y, Yin Y. Melatonin application confers enhanced salt tolerance by regulating Na+ and Cl−accumulation in rice. Plant Growth Regulation. 2017; 83:441-454. DOI: 10.1007/s10725-017-0310-3.

 Kołodziejczyk I, Dzitkob K, Szewczyk R, Posmyka MM. Exogenous melatonin improves corn (Zea mays L.) embryo proteome in seeds subjected to chilling stress. Journal of Plant Physiology. 2016; 193:47-56. DOI: 10.1016/j.jplph.2016.01.012

 Korkmaz A, Karaca A, Kocacinar F, Cuci Y. The effects of seed treatment with melatonin on germination and emergence performance of pepper seeds under chilling stress. Tarım Bilimleri Dergisi. 2017; 23:167-176

 Kratsch HA, Wise RR. The ultrastructure of chilling stress. Plant, Cell & Environment.

2000; 23:337-350

 Kusvuran S, Ellialtioglu S, Polat Z. Antioxidative enzyme activity, lipid peroxidation, and proline accumulation in the callus tissues of salt and drought tolerant and sensitive pumpkin

(21)

genotypes under chilling stress. Horticulture, Environment and Biotechnology. 2013; 54:319- 325. DOI: 10.1007/s13580-013-1042-6

 Lee, H.Y.; Back, K. Melatonin induction and its role in high light stress tolerance in Arabidopsis thaliana.J. Pineal Res. 2018, 65, e12504. (CrossRef)

 Lei XY, Zhu RY, Zhang GY, Dai YR. Attenuation of cold-induced apoptosis by exogenous melatonin in carrot suspension cells: The possible involvement of polyamines. Journal of Pineal Research. 2004; 36:126-131

 Lerner AB, Case JD, Takahashi Y, Lee TH, Mori W. Isolation of melatonin, a pineal factor that lightens melanocytes. Journal of the American Chemical Society. 1958; 80:2587

 Leyva R, Sánchez-Rodríguez E, Ríos JJ, Rubio-Wilhelmi MM, Romero L, Ruiz JM, et al.

Beneficial effects of exogenous iodine in lettuce plants subjected to salinity stress. Plant Science. 2011; 181:195-202. DOI: 10.1016/j.plantsci.2011.05.007

 Li C, Tan DX, Liang D, Chang C, Jia D, Ma F. Melatonin mediates the regulation of ABA metabolism, free-radical scavenging, and stomatal behavior in two Malus species under drought stress. Journal of Experimental Botany. 2015; 66:669-680

 Li D, Zhang D, Wang H, Li Y, Li R. Physiological response of plants to polyethylene glycol (PEG-6000) by exogenous melatonin application in wheat. Zemdirbyste-Agriculture.

2017;104(3):219-228. DOI: 10.13080/z-a.2017.104.028

 Li H, Chang J, Chen H, Wang Z, Gu X, Wei C, et al. Exogenous melatonin confers salt stress tolerance to watermelon by improving photosynthesis and redox homeostasis. Frontiers in Plant Science. 2018; 8:295. DOI: 10.3389/fpls.2017.00295

 Li H, He J, Yang X, Li X, Luo D, Wei C. Glutathione-dependent induction of local and systemic defense against oxidative stress by exogenous melatonin in cucumber (Cucumis sativus L.). Journal of Pineal Research. 2016;60:206-216. DOI: 10.1111/jpi.12304

 Li J, Zeng L, Cheng Y, Lu G, Fu G, Ma H, et al. Exogenous melatonin alleviates damage from drought stress in Brassica napus L. (rapeseed) seedlings. Acta Physiologiae Plantarum.

2018; 40:43. DOI: 10.1007/s11738-017-2601-8

 Li, C.; Tan, D.-X.; Liang, D.; Chang, C.; Jia, D.; Ma, F. Melatonin mediates the regulation of ABA metabolism, free-radical scavenging, and stomatal behaviour in two Malus species under drought stress. J. Exp. Bot. 2014, 66, 669–680. (CrossRef) (PubMed)

 Li, C.; Wang, P.; Wei, Z.; Liang, D.; Liu, C.; Yin, L.; Jia, D.; Fu, M.; Ma, F. The mitigation effects of exogenous melatonin on salinity-induced stress in Malus hupehensis. J. Pineal Res.

2012, 53, 298–306. (CrossRef) (PubMed)

 Li, H.; Chang, J.; Chen, H.; Wang, Z.; Gu, X.; Wei, C.; Zhang, Y.; Ma, J.; Yang, J.; Zhang, X. Exogenous melatonin confers salt stress tolerance to watermelon by improving photosynthesis and redox homeostasis. Front. Plant Sci. 2017, 8, 295. (CrossRef) (PubMed)

 Li, H.; Chang, J.; Zheng, J.; Dong, Y.; Liu, Q.; Yang, X.; Wei, C.; Zhang, Y.; Ma, J.; Zhang, X. Local melatonin application induces cold tolerance in distant organs of Citrullus lanatus L. via long distance transport. Sci. Rep. 2017, 7, 40858. (CrossRef) (PubMed)

 Li, J.; Li, Y.; Tian, Y.; Qu, M.; Zhang, W.; Gao, L. Melatonin Has the Potential to Alleviate Cinnamic Acid Stress in Cucumber Seedlings. Front. Plant Sci. 2017, 8, 1193. (CrossRef) (PubMed)

 Li, J.; Zeng, L.; Cheng, Y.; Lu, G.; Fu, G.; Ma, H.; Liu, Q.; Zhang, X.; Zou, X.; Li, C.

Exogenous melatonin alleviates damage from drought stress in Brassica napus L.(rapeseed) seedlings. Acta Physiol. Plant. 2018, 40,43. (CrossRef)

(22)

 Li, X.; Wei, J.-P.; Scott, E.; Liu, J.-W.; Guo, S.; Li, Y.; Zhang, L.; Han, W.-Y. Exogenous melatonin alleviates cold stress by promoting antioxidant defense and redox homeostasis in Camellia sinensis L. Molecules 2018, 23, 165.(CrossRef)

 Li, Z.-G.; Xu, Y.; Bai, L.-K.; Zhang, S.-Y.; Wang, Y. Melatonin enhances thermotolerance of maize seedlings (Zea mays L.) by modulating antioxidant defense, methylglyoxal detoxification, and osmoregulation systems. Protoplasma 2019, 256, 471–490. (CrossRef)

 Liang C, Li A, Yu H, Li W, Liang C, Guo S, et al. Melatonin regulates root architecture by modulating auxin response in rice. Frontiers in Plant Science. 2017;8:134. DOI:

10.3389/fpls.2017.00134 .

 Liang C, Zheng G, Li W, Wang Y, Hu B, Wang H, et al. Melatonin delays leaf senescence and enhances salt stress tolerance in rice. Journal of Pineal Research. 2015;59:91-101. DOI:

10.1111/jpi.12243

 Liang, D.; Gao, F.; Ni, Z.; Lin, L.; Deng, Q.; Tang, Y.; Wang, X.; Luo, X.; Xia, H. Melatonin improvesheat tolerance in kiwifruit seedlings through promoting antioxidant enzymatic activity and glutathione S-transferase transcription. Molecules 2018, 23, 584. (CrossRef)

 Liu Y, Jiang H, Zhao Z, An L. Nitric oxide synthase like activity-dependent nitric oxide production protects against chilling induced oxidative damage in Chorispora bungeana suspension cultured cells. Plant Physiology and Biochemistry. 2010;48:936-944. DOI:

10.1016/j.plaphy.2010.09.001

 Liu, J.; Wang, W.; Wang, L.; Sun, Y. Exogenous melatonin improves seedling health index and droughttolerance in tomato. Plant Growth Regul. 2015, 77, 317–326. (CrossRef)

 Loureiro S, Santos C, Pinto G, Costa A, Monteiro M, Nogueira AJA, et al. Toxicity assessment of two soilsfrom Jales mine (Portugal) using plants: Growth and biochemical parameters. Archives of Environmental Contamination and Toxicology. 2006; 50:182-190

 Lyons JM. Chilling injury in plants. Annual Review of Plant Physiology. 1973; 24:445-466

 Ma X, Zhang J, Burgess P, Rossi S, Huang B. Interactive effects of melatonin and cytokinin on alleviating drought induced leaf senescence in creeping bentgrass (Agrostis stolonifera).Environmental and Experimental Botany. 2018; 145:1-11. DOI:

10.1016/j.envexpbot.2017.10.010

 Mahajan S, Tuteja N. Cold, salinity ve drought stres: An overwiev. Archives of Biochemistry and Biophysics. 2005;444:139-158. DOI: 10.1016/j.abb.2005.10.018

 Marta, B.; Szafra ´nska, K.; Posmyk, M.M. Exogenous melatonin improves antioxidant defense in cucumber seeds (Cucumis sativus L.) germinated under chilling stress. Front.

Plant Sci. 2016, 7, 575. (CrossRef) (PubMed).

 Martinez, V.; Nieves-Cordones, M.; Lopez-Delacalle, M.; Rodenas, R.; Mestre, T.; Garcia- Sanchez, F.; Rubio, F.;Nortes, P.; Mittler, R.; Rivero, R. Tolerance to stress combination in tomato plants: New insights in the protective role of melatonin. Molecules 2018, 23, 535.

(CrossRef)

 Meng JF, Xu TF, Wang ZZ, Fang YL, Xi ZM, Zhang ZW. The ameliorative effects of exogenous melatonin on grape cuttings under water-deficient stress: Antioxidant metabolites, leaf anatomy, and chloroplast morphology. Journal of Pineal Research. 2014; 57:200-212.

DOI: 10.1111/jpi.12159

 Monakhova OF, Chernyadev II. Protective role of kartolin-4 in wheat plants exposed to soil drought. Applied and Environmental Microbiology. 2002; 38:373-380

(23)

 Moussaa HR, Algamal SMA. Does exogenous application of melatonin ameliorate boron toxicity in spinach plants? International Journal of Vegetable Science. 2017;23(3):233-245.

DOI: 10.1080/19315260.2016.1243184(89) Pierce LC. Vegetables. Characteristics, Production and Marketing. USA: John Willey and Sons Inc.; 1987. 433 p

 Mukherjee, S.; David, A.; Yadav, S.; Baluška, F.; Bhatla, S.C. Salt stress-induced seedling growth inhibition coincides with differential distribution of serotonin and melatonin in sunflower seedling roots and cotyledons. Physiol. Plant. 2014, 152, 714–728. (CrossRef) (PubMed)

 Munns R, Tester M. Mechanisms of salinity tolerance. Annual Review of Plant Biology.

2008;59:651-681. DOI: 10.1146/annurev.arplant.59.032607.092911

 Murch SJ, Campbell SS, Saxena PK. The role of serotonin and melatonin in plant morphogenesis: Regulation of auxininduced root organogenesis in in vitro-cultured explants of St. John’s Wort (Hypericum perforatum L.). In Vitro Cellular & Developmental Biology.

Plant. 2001; 37:786-793

 Murch SJ, KrishnaRaj S, Saxena PK. Tryptophan is a precursor for melatonin and serotonin biosynthesis in in vitro regenerated St. John’s Wort (Hypericum perforatum L. Cv. Anthos) plants. Plant Cell Reports. 2000; 19:698-704

 Murch SJ, Simmons CB, Saxena PK. Melatonin in feverfew and other medicinal plants.

Lancet. 1997; 350:1598-1599

 Nawaz MA, Huang Y, Bie Z, Ahmed W, Reiter RJ, Niu M. Melatonin: Current status and future perspectives in plant science. Frontiers in Plant Science. 2016; 6:1230. DOI:

10.3389/fpls.2015.01230.

 Nawaz MA, Jiao Y, Chen C, Shireen F, Zheng Z, Imtiaz M, et al. Melatonin pretreatment improves vanadium stress tolerance of watermelon seedlings by reducing vanadium concentration in the leaves and regulating melatonin biosynthesis and antioxidant-related gene expression. Journal of Plant Physiology. 2018; 220:115-127. DOI:

10.1016/j.jplph.2017.11.003

 Nawaz, M.A.; Jiao, Y.; Chen, C.; Shireen, F.; Zheng, Z.; Imtiaz, M.; Bie, Z.; Huang, Y.

Melatonin pretreatment improves vanadium stress tolerance of watermelon seedlings by reducing vanadium concentration in the leaves and regulating melatonin biosynthesis and antioxidant-related gene expression. J. Plant Physiol. 2018, 220, 115–127. (CrossRef)

Melatonin pretreatment improves vanadium stress tolerance of watermelon seedlings by reducing vanadium concentration in the leaves and regulating melatonin biosynthesis and antioxidant-related gene expression. J. Plant Physiol. 2018, 220, 115–127. (CrossRef) (PubMed)

Melatonin pretreatment improves vanadium stress tolerance of watermelon seedlings by reducing vanadium concentration in the leaves and regulating melatonin biosynthesis and antioxidant‐related gene expression. J. Plant Physiol. 2018, 220, 115–127.

 Ni J, Wang Q, Shah FA, Liu W, Wang D, Huang S, et al. Exogenous melatonin confers cadmium tolerance by counterbalancing the hydrogen peroxide homeostasis in wheat seedlings. Molecules. 2018; 23:799. DOI: 10.3390/molecules23040799

 Ni, J.; Wang, Q.; Shah, F.A.; Liu, W.; Wang, D.; Huang, S.; Fu, S.; Wu, L. Exogenous Melatonin Confers Cadmium Tolerance by Counterbalancing the Hydrogen Peroxide