Alleviative Effects Of 24-Epibrassinoslide On Protected Tomato Seedlings Subjected To Low Temperature And Poor Light

Tomato?Lycopersicon esculentum Mill.?in different growth period is most likely to suffer from low temperature and poor light damage in Winter and Spring.Growth,development and organ formation of tomato are affected,eventually resulting in a decline in the quality and yield.A lot of research results showed that brassinolide could obviously improve the low temperature and poor light resistances of tomato.Therefore,it is very important to study the physiological and biochemical mechanisms.Two tomato cultivars differing in low temperature and poor light resistances?‘Zhongza 9' was stronger than ‘Zhongshu4' in stress resistance?were used as experimental material.Seedlings were pre-treated with foliar sprays of 0.1 mg·L-1 or 0.0 mg·L-1?control?EBR and then grown in an environmental chamber simulating conditions of low temperature?12°C/6°C,day/night?and poor light?80 ?mol· m-2· s-1?.The effects of EBR on the antioxidant activity of superoxide dismutase,catalase and peroxidase,photosynthetic character and chlorophyII fluorescence parameters were studied.At the same time,the stress-tolerant protein was screened and the screening gene was carring on function verification.The experiment's aim was to reveal the physiology and biochemical mechanisms of exogenous EBR improving low temperature and poor light stress tolerances of tomato.The results were as follows:1.After low temperature and poor light stress treatments,the antioxidant activities of superoxide dismutase?SOD?and peroxidase?POD?showed upward trend firstly,then downward.The activity of catalase?CAT?declined,and the content of malondialdehyde?MDA?increased.Exogenous EBR could improve the activities of SOD?POD and CAT,and decrease the reactive oxygen?ROS?level.The content of MDA was reduced and the cell membrane peroxidation damage was alleviated.These enhanced the ability of stress tolerance to low temperature and poor light in tomato.2.Under low temperature and poor light stress conditions,the net rate of photosynthesis?Pn?,stomatal conductance?Gs?and transpiration rate?Tr?were gradually reduced in the leaves from both tomato cultivars,whereas intercellular CO2 concentration?Ci?increased.These demonstrated that the limitation to Pn was non-stomatal.Exogenous EBR could ease the decline in photosynthesis,and remove the photoinhibition of low temperature and poor light stresses to tomato seeding leaves.3.Values for Fv/Fm,Fv?/Fm?,Qp and ?PSII tended to decrease in tomato seedling leaves when plants were grown under our combined stress conditions.Exogenous EBR pretreatment significantly alleviated this drop in chlorophyII fluorescence parameters and alleviated the damage degree of tomato seedling leaves in low temperature and poor light conditions.4.Through the SDS-PAGE gel,protein content determination and MALDI-TOF/TOF MS,exogenous EBR pretreatment could increase the content of ATP synthase ? subunit.This could activate the biological energy metabolism and improve ATP level.5.Secondary structure and tertiary structure of ATP synthase ? subunit were predicted by bioinformatics method.ATP synthase ? subunit contained multiple phosphorylation sites.The seven binding site residues were A₁₇₄,G₁₇₅,V₁₇₆,G₁₇₇,K₁₇₈,T₁₇₉,and R₂₀₅ and seven active site residues were T₃₀₄,G₃₀₇,L₃₀₉,E₃₁₁,A₃₄₀,A₃₄₄,and L₃₄₆.Throgh constructing phylogenetic tree,the ATP synthase ? subunit could be in chloroplast.6.Resistance experiments to low temperature were done in T1 generation of tomato seedlings of ATP synthase ? subunit overexpression.It was found that the resistance to low temperature of transgenetic plants was enhanced.Transgenetic tomato seedlings could reduce the reactive oxygen species?ROS?level by improving the SOD,POD and CAT activities in cells under low temperature condition.MDA content was reduced.Transgenetic tomato seedlings could improve the contents of chlorophyII a and chlorophyII b under low temperature condition.Thus,transgenetic plants could improve the light energy conversion efficiency.Photosynthetic ability of transgenetic tomato seedling was also significantly higher than the wild type.