Effect Of Exogenous NO On Photosynthetic Carbon Assimilation In Tomato Seedlings Under NaCl Stress

Salt stress is one of the most important abiotic stresses limiting crop growth and development in crop cultivation. Tomato is one of the most important vegetable crops cultivated and the demand of market for it is large, but due to the serious facilities of soil secondary salinization, resulting in a serious decline in yield and quality of tomato. Therefore, it is crunch time for research to improve the salt tolerance of tomato. In this study, tomato cultivar "Baiguo Qiangfeng" was used as experiment material, and effects of exogenous NO on the morphological indexes, photosynthetic carbon assimilation, antioxidant system and micro regional distribution of mineral elements in tomato seedlings under salt stress was investigated. The main results were presented as follows:1. NaCl stress significantly restrained the growth of tomato seedlings. Exogenous NO significantly alleviated the growth of tomato seedlings under NaCl stress.2. NaCl stress decreased net photosynthetic rate, increased the dark respiration rate, decreased the apparent quantum efficiency of photosynthesis, Rubisco maximum carboxylation efficiency and RuBP regeneration rate, also significantly inhibited the activity of Rubisco and RCA and FBPase, as well as the expression levels of key genes in photosynthetic carbon assimilation, declined the photosynthesis rate of tomato leaves, inhibited the accumulation of photosynthetic product, which inhibited the normal growth and development of tomato seedlings. Exogenous nitric oxide through up the expression levels of key genes in photosynthetic carbon assimilation, improved the activity of photosynthetic carbon assimilation enzyme Rubisco and RCA and FBPase, increased the apparent quantum efficiency of photosynthesis,Rubisco maximum carboxylation efficiency and RuBP regeneration rate, depressed the dark respiration rate,mitigated the damage of photosynthetic apparatus under Na Cl stress, and improved the net photosynthetic rate, the accumulation of photosynthate product, and effectively alleviated inhibition of seedling growth in tomato under Na Cl stress.3. NaCl stress inhibited the reduced redox state, increased oxidative stress, produced a large amount of reactive oxygen, and significantly down regulated the activity of antioxidant enzymes and the expression level of mRNA of most antioxidant enzymes, accumulated a large amonunt of active oxygen can not be cleared in time, increased membrane lipid peroxidation, and effected the growth of tomato seedlings under Na Cl stress. Exogenous nitric oxide significantly increased the reduced redox state and the activity of antioxidant enzymes and the expression level of mRNA of most antioxidant enzymes, effectively removed the large number of active oxygen, reduced membrane lipid peroxidation level, and effectively alleviated inhibition of seedling growth in tomato under NaCl stress.4. NaCl stress decreasd the root activity of tomato seedlings, and inhibited the capacity of the drop of water and mineral elements absorption and transport, resulted the region K, Mg and Ca contentin in leaves and roots of plants be decreased, but also accumulated a large amount of salt ions of Na+ and Cl-damage, caused leaves occur away from the toxic effects of plant growth. Exogenous NO could effectively improved the root activity of tomato seedlings, increased in leaves and roots of K, Mg and Ca content,reducd the relative content of Na and Cl elements, alleviated salt harmful ions on Tomato Seedling of poison, promoted the normal growth of tomato seedlings under NaCl stress.