| Saline soil accumulated large amounts of salt ions, and these high concentrations of salt ions in top soil could form a salt stress environment to crops. Salt stress can seriously affect the growth and development of crops and led to yield and quality reduction. Facility cultivation is an important way of vegetable production, but the secondary salinization problem in the cultivation process seriously restricted the development of greenhouse vegetable cultivation.Tomato is one of the vegetable species which have the most widely cultivation area and the lagrest consumption in facility cultivation. Soil salinization can cause the growth and development of tomato lagging, smaller and deformity fruit increaseing, yield and quality declined. So, it seriously affected the economic benefits of planting production.In this study, taking the tomato cultivar ‘Jinpeng No.1’ as the experimental material, we investigated the effects of root irrigating exogenous melatonin on photosynthesis characteristic, chlorophyll content, fluorescence parameters, osmotic regulation substances content and the change of the protective enzyme activity in the tomato feedlings under 150mmol/L NaCl stress. And the yield and quality of tomato fruit were also measured under different treatments. These results were analyzed to explore the function for exogenous melatonin alleviated salt damage, improved field and quality. The results were presented as follows:1. Melatonin treatment significantly increased the content of chlorophyll and carotenoid in tomato seedlings leaves under salt stress, improved the gas exchange parameters: net photosynthetic rate(PN), transpiration rate(Tr) and stomatal conductance(Gs); The maximum photochemical quantum yield of reaction center PSII(Fv/Fm), actual light quantum yield(Φ PSII), coefficient of photochemical quenching(qP), non photochemical quenching(NPQ), apparent electron transport rate(ETR) in melatonin treatment were also significantly higher than that under salt stress. These indicators increased firstly and then decreased with the concentration of melatonin increased, and reached its maxmium under the 50 mmol/L melatonin treatment. At the same time, the intercellular CO2 concentration(Ci) and initial fluorescence(Fo) reached minimum under 50 μmol/L treatment. These results suggested that exogenous melatonin promoted the accumulation of photosynthetic pigment, effectively protected the stability of the photosynthetic apparatus, maintained the activity of the reaction center PSII, improved the photosynthetic electron transport rate and efficiency of light energy utilization, enhanced the photosynthesis of tomato seeldins.2. Melatonin treatment significantly increased the content of osmotic regulation substances: proline(Pro)and soluble protein in tomato seedlings under salt stress. In 50 μmol/L treatment,they reached the maximum. This suggested melatonin involved in the process of plant osmotic regulation,reduced salt stress caused by osmotic stress, and reduced cell moisture loss.3. Melatonin treatment significantly increased the activity of super oxide dismutase(SOD), peroxidase(POD) and catalase(CAT) stress, and reduced the malonic aldehyde(MDA) content in tomato seedlings leaves under salt stress. This suggested melatonin promoted higher protection enzyme activity, improved the ability of clearing up ROS, reduced the injury of membrane lipid peroxidation to the plant cell, and relieved the oxidative stress caused by salt stress.4. Melatonin treatment significantly increased the yield per unit area of tomato plants under salt stress, increased the content of soluble sugar, soluble solids, soluble protein, sugar acid ratio, ascorbic acid and beta carotene, reduced the content of organic acid and nitrate, improved the quality of the tomato fruit. These improvements were best under the 50-100 μmol/L treatment.5. Melatonin treatment significantly increased the content of volatile aromatic substances in fruits under salt stress, enhanced the fruit characteristic fresh smell. The aroma components were also involved in regulation of plant art reaction. Total volatile substances increases firstly and then deareased with the concentration of melatonin increased, and all kinds of volatile component content also showed the same trend, During these treatmens, the total volatile substances was the largest under the 50 μmol/L melatonin treatment. |
