Influence Of Exogenous Melatonin On Tomato Antioxidant System And Yield And Fruit Quality Under Drought Stress

In recent years, along with the impact of global warming and excessive chemical fertilizer can weaken the soil water retention, reduce the available water content in the soil. Drought stress has become the main environmental factors affecting plant cultivation in protected field. It has the effect on the growth, quality and yield of plant. Tomato is the major vegetables in the protected culitivation. It demanded large water in the growth process. Drought stress can cause the plants harmed and a series of changes in external morphology, physiological and biochemical characteristics to plants, ultimately affect the growth and development process, the yield and quality of tomato was affected, and the decrease of economic benefit.In our study, tomato(Jinpeng No.1) was chosen as the experimented materials, the effects of melatonin on the health index and the effects of melatonin treatment on the plant growth, photosynthesis characteristic, active oxygen metabolism and accorbate metabolism under drought stress. Tomato(Jinpeng No.1) was chosen as the other experimented materials, explore the effect of melatonin treatment on the yield and the quality of tomato fruit(sugar, acid, lycopene). We have investigated the effects of melatonin on the health index and drought tolerance of tomato. The results showed as followed:(1) Melatonin primarily affects root dry weight and crown dry weight, thereby increasing the capacity to absorb water and nutrients and improving biomass production.(2) Melatonin pretreatment can significantly increase the root activity, the net photosynthesis rate(Pn), stomatal conductance(Gs), transpiration rate(Tr), and chlorophyll content of tomato under drought stress. During the salt treatment of 10 days, the rate of these increased intensively. Intercellular CO2 concentration(Ci), the initial fluorescence(F0), PSII practical quantum efficiency(ΦPSII), PSII maximum quantum efficiency(Fv/Fm) could keep stable. These results suggest that melatonin pretreatment can effectively enhanced water uptake, and more efficient use of soil water during imposed drought, protect the photochemical reaction center of tomato seedlings, improve the efficiency of energy conversion leaves, promote the accumulation of photosynthetic pigments, enhance photosynthesis, increase the growth of tomato seedlings, and improve the drought tolerances of tomato seedlings.(3) Melatonin pretreatment can significantly decreased the MDA and O2- content and increased the activity of SOD, CAT, POD during the drought stress. These results demonstrated that melatonin pretreatment may inhibite the generation of active oxygen species, improve the activity of antioxidant enzymes and antioxidants contents, decrease the membrane lipid peroxidantion, it can ease the damage by drought treatment. Meanwhile the addition of melatonin can increased the As A content, which may improve the expression of APx and GR activities in As A-GSH cycle and enhance the ability of scavenging H2O2 and inhibite the accumulation of active oxygen species, alleviate the damage degree caused by salinity treatment and improve the salt tolerances.(4) Under drought stress, melatonin treatment significantly increased the content of ascorbic acid, citric acid, and Ca2+, soluble solids content decreased.