Effects Of Melatonin Application On Physiological Characteristics Under Salt And Drought Stress Condition,anti-aging And Hormonal Response Of Summer Maize In Grain Filling Stage

Abiotic stress can cause a wide range of damages in plant morphology;physiology and structure,which eventually leads to decreasing crop production.Water scarcity is one of the major environmental constraints which limits negatively affect the crop growth and yield.Water scarcity induces the overproduction of reactive oxygen species?ROS?.It causes oxidative damages to cell membranes,degrades photosynthetic pigments,proteins,enzymes activity,and reducing production.Plant growth regulators?PGRs?play a crucial role in the physiological function of crops under stress conditions.Melatonin is an important biologically active hormone that plays a vital role in plant growth and development,especially in abiotic stress conditions.In this study,the pot experiment and two years of field experiments were conducted.The pot experiment was conducted to study the exogenous application of PGRs melatonin on maize seedling by maintaining plant growth,improving the photosynthetic characteristics and activities of antioxidants enzymes under drought and salt stress conditions.Also,a two-year field experiment was carried out to study the exogenous application of melatonin for seed soaking and foliar application at the ninth leaf stage on delaying leaf senescence,antioxidant defense mechanism,hormonal response,seed filling rate and maize yield under the semi-arid region.According to the present research work,the main findings are as follows:1.The pot experiment was carried out to investigate the protective role of melatonin in photosynthetic traits and the antioxidant defense system of maize seedling under drought stress.Maize seedlings were subjected to drought stress?40-45% FC?after two weeks of seedling emergence,followed by a foliar spray?0,25,50,75 and 100 ?M?and soil drench of melatonin?0,25,50,75 and 100 ?M?.Our results indicated that after 20 days of melatonin application,the root length increased by 9.9% to 43.5% and root diameter increased by 34.9% and 19.0%.The leaf superoxide dismutase?SOD?and peroxide?POD?increased by 61.2% & 55.1%,and 46.5% &57.1% and catalase?CAT?activity by 57.1% & 64.0% respectively,while significantly reduced the hydrogen by 38.1% & 43.7% and MDA content by 59.1% & 52.8% respectively.The soluble protein contents was increased by 94.3% & 118.2% and proline contents by 55.3% & 31.5% with melatonin application under drought stress condition.The lower hydrogen peroxide content?H₂O₂?,malondialdehyde content?MDA?and higher soluble protein,proline and anti-oxidant enzymes activities protected the photosynthetic machinery and improved the chlorophyll content by 80.4% & 80.6% and photosynthetic activity by 56.8% & 21.2% under drought stress conditions.Our findings showed that foliar application of 100 ?M and soil drench of 50 ?M melatonin was the most effective treatment concentrations under drought stress.Our current findings hereby confirmed the mitigating potential of melatonin application for drought stress by maintaining plant growth,improving the photosynthetic characteristics and activities of antioxidant enzymes.2.Salt stress reduced the plant growth characteristics and photosynthetic efficiency by increasing the ROS accumulation and reducing the antioxidant enzyme activities.However,exogenous application of melatonin significantly increased plant salt stress tolerance at the seedling stage.In this study,we investigated the role of melatonin by measuring the photosynthetic characteristics and antioxidant defense system of maize seedling under salt stress?200 m M Na Cl?at the seventh leaf stage and were treated with different concentrations of melatonin?MT1-30,MT₂-60,and MT₃-90 ?M?.Our results revealed that exogenous application of melatonin?60 ?M?under salt stress conditions significantly increased the growth characteristics of plants,chlorophyll content by 82.4%,photosynthetic efficiency by 29.5%,antioxidant enzymes activities i.e.superoxide dismutase?SOD?by 41.8%,peroxide?POD?by 34.6%,catalase?CAT?by 10.2% and ascorbate peroxidase?APX?by 15.8%,and reduced the reactive oxygen species H₂O₂ by 21.6%,MDA by 22.7%.The optimal concentration of melatonin 60 ?M as a soil drenching was the most effective for maize seedling under salt stress conditions.3.Premature leaf senescence leads to the disintegration of chloroplasts and degradation of chlorophyll pigment in the later growth stages of maize crop.The objectives of the current research were to evaluate the effect of foliar application of melatonin?MF?on photosynthetic efficiency,antioxidant defense mechanism and its relation with leaf senescence in maize crop grown in a semi-arid region.A field experiment was conducted during the 2017 and 2018 growth season,where melatonin was applied to the foliage at concentrations of 0?MF₀?,25?MF₁?,50?MF₂?and 75?MF3??M at the ninth leaf stage.Foliar application of melatonin significantly improved chlorophyll content by 72.5% & 61.3 %,net photosynthetic rate by 20.5 % & 26.5%,soluble sugar content by 17.4% & 25.6%,and soluble protein content by 46.4% & 25.3% during the process of leaf senescence in both growing seasons.The application of melatonin also enhanced antioxidant enzyme activities including superoxide dismutase by 27.8% & 26.6%,catalase by 23.8% & 19.8%,and peroxidase by 51.6% & 38.1%,while reduced malondialdehyde by 47.6% & 26.4% and reactive oxygen species accumulation.Melatonin foliar application also increased total leaf area per plant by 25.9 % & 19.4%,grains per ear by 24.5% & 22.1%,hundred grain weight by11.8% & 16.8% and grain yield by 46.3% & 42.1% of maize crop in a semi-arid region.The application of melatonin significantly improved photosynthetic activity,antioxidant defense,and yield of maize crop in a semi-arid region,where the most effective treatment was MF₂?50 ?M?.4.The application of exogenous melatonin is valuable for plant growth and improving the maize yield in semi-arid regions.In this research,we studied the protective role of melatonin application on grain filling rate and hormonal regulations in maize grains under field conditions in the summer seasons during 2017 and 2018.Our results revealed that the melatonin treatment as seed soaking significantly increased single seed weight,seed filling rate in middle,superior,and inferior seeds by regulating the hormone levels compared with the foliar application.Application of melatonin significantly increased the zeatin + zeatin riboside?Z+ZR?,indole-3-acetic acid?IAA?,gibberellic acid?GA?contents,however,significantly inhibited the contents of abscisic acid?ABA?during the seed filling period.The Z + ZR,IAA and GA contents were positively correlated with maximum seed filling rate,maximum seed weight and mean filling rate in middle seeds,superior and inferior seeds,while ABA contents were negatively correlated.The ABA contents in inferior seeds were positively correlated with mean seed filling and maximum seed filling rate.Melatonin treatment of SM₂?50 ?M?and FM₂?50 ?M?significantly increased the dry matter plant-1,hundred seed weight,seed filling rate,IAA,Z+ZR,GA contents,ear characteristics and grain yield of maize under semi-arid regions.