Effects Of Exogenous Spermidine On Rubisco And Mitochondrial Function Mechanism Of Tomato Seedlings Under Salinity-alkalinity Mixed Stress

In recent years, the yield and quality of tomato affected by the aggravated secondary salinization of soil in protected agriculture. Spermidine(Spd), which was a bioactive low molecular weight aliphatic nitrogen compounds, could effectively relieve the damage in response to biotic and abiotic stress.The research for exogenous Spd alleviate saline-alkaline stress to protection mechanism of mitochondria and the impact of Rubisco were less, so it is necessary to further study of exogenous Spd on the role of mitochondrial function and photosynthetic key enzyme-Rubisco on salt toxictity in plant. saline In order to explore the physiological and biochemical mechanism of spermidine(Spd) increased the saline-alkaline tolerance of tomato(Solanum lycopersicum) seedlings. In this experiment, two tomato cultivars(cv. ‘Jinpeng chaoguan’ is a highly salt-tolerant ecotype, while cv. ‘Zhongza No. 9’is more salt-sensitive ecotype) were used, the effect of foliar-spraying 0.25 mmol·L-1exogenous Spd on rubisco and mitochondrial function of tomato seedlings under 75 mmol·L-1saline-alkaline condition were studied. The main results as follows:1. Effects of exogenous Spd on root growth of Tomato under saline-alkaline stress:Compared with control, saline-alkaline stress restrained the crown root growth of two tomato seedlings: root length, root surface area, root volume, and root tips were significantly reduced,root activity with the extension of stress time also decreased significantly. Besides, there was greater influence on ‘Zhongza No. 9’.Under salinity stress, foliar spraying exogenous Spd effectively ease the stress on the two varieties of tomato seedling root growth inhibition,effectively increase the root activity, so as to promote plant growth.2. Effects of exogenous Spd on the mitochondrial structure of tomato roots under saline-alkaline stress: Saline-alkaline stress destroyed the mitochondrial ultrastructure,mitochondria swelled irregularly and their cristae fractured and become fuzzy.Compared to‘Zhongza NO.9’,in ‘Jinpengchaoguan’ the mitochondrial structure damage degree of light,some ware holding the complete structure. Under saline-alkaline stress, foliar-spraying exogenous Spd effectively holding cell structure 、 mitochondrial membrane structure compared to stress, crest rich and clear, only part of inclusions were cavitation.The roots of the CK treatment of two varieties comparison clear nuclei and cell mitochondria in good condition, assumes the circular or elliptic, and have a full double membrane structure.Normalcultivation conditions, CK and exogenous spraying Spd processing two varieties of cell structure, mitochondrial membrane structure had no significant difference.3. Effects of exogenous Spd on the mitochondrial function of tomato roots under saline-alkaline stress:Saline-alkaline stress increased the concentrations of both mitochondrial H2O2 and MDA as well as mitochondrial membrane permeability in the roots of the two cultivars, while it decreased the mitochondrial membrane fluidity, membrane potential, Cyt c/a and H+-ATPase 、H+-PPiase、Ca2+-ATPase、Mg2+-ATPase activity, which impaired the mitochondria and therefore inhibited the root growth; and these effects were more obvious in‘Zhongza No.9’than in ‘Jinpengechaoguan’.Under the salinity-alkalinity stress,foliar application Spd could effectively decrease the concentrations of mitochondrial H2O2 and MDA and mitochondrial membrane permeability,while increased the mitochondrial membrane fluidity, membrane potential, Cyt c/a and H+-ATPase 、H+-PPiase、Ca2+-ATPase、Mg2+-ATPase activity. These results suggest that exogenous Spd could effectively mitigate the damage on mitochondria induced by salinity-alkalinity stress, and the alleviative effect was more obvious in ‘Zhongza No.9’ than ‘Jinpengchaoguan’.4. Effects of exogenous Spd on Photosynthesis and Rubisco of Tomato under saline-alkaline stress: Under Saline-alkaline stress, the seedling growth of the two tomato cultivars was inhibited. The net photosynthetic rate, stomatal conductance, transpiration rate,initial and total activity of rubisco, as well as content of rubisco were all significantly reduced under saline-alkaline stress. Besides, there was greater influence on ‘Zhongza No. 9’. The main limiting factor of photosynthesis in ‘Zhongza No. 9’ tomato seedling was non-stomatal factor under saline-alkaline stress, while it was stomatal factor for‘Jinpengchaoguan’. Under stress conditions, exogenous foliar spraying Spd could significantly improve the shoots growth, net photosynthetic rate, stomatal conductance, transpiration rate, increased the activity of rubisco and content of rubisco of both tomato cultivars. Moreover, the inhibition of carbon assimilation, as well as the stomatal and non-stomatal limitation, caused by salinity-alkalinity stress, could be effectively reduced by exogenous Spd, meanwhile, at the late of stress,Spd can significantly increased the content of rubisco activase of both tomato cultivars, and the alleviative effect of Spd treatment on saline-alkaline damages was more obvious in ‘Zhongza No. 9’ cultivar.