Effects Of Heat Stress On Antioxidant Capacities And Carbohydrate Metabolism Of Chloroplast In Non-heading Chinese Cabbage Seedlings

Non-heading Chinese cabbage is a cruciferous,annual herb.It prefers the cool climate.In summer,high temperature will cause shoot and root growth inhibition,high seedling establishment rate,serious viruses,rolling and dry of leaves,even necrosis.With the temperature constantly rising in recent years,It is important for selecting and breeding of heat-tolerance variety to evaluation non-heading Chinese cabbage systematically and study its heat mechanisms.In present study,two non-heading Chinese cabbage‘xd'?heat tolerant?and‘sym'?heat-susceptible?were selected as experiment material with different sensitivity to heat stress.Growth parameters,photosynthetic and fluorescent characteristics,chloroplast ultrastructure,oxidative damage,antioxidant capacity and carbohydrate metabolism of chloroplast in non-heading Chinese cabbage seedlings were evaluated after 6 days high temperature treatment?37??.The main results are as follows:1.We choosed‘xd'?heat tolerant?and‘sym'?heat-susceptible?as main experiment material though measuring semi-lethal temperatures of 12 non-heading Chinese cabbage cultivars.The semi-lethal temperatures of‘xd'and‘sym'are 39.45?and 35.29?respectively.2.High temperature stress resulted in spindly growth of seedlings.The plant height was increased while stem diameter,single weight were significantly decreased after 6 days heat stress.Compared to heat-susceptible‘sym',less increase in plant height and less decreases in stem diameter,single weight were showed in the heat-tolerant‘xd'.3.After high temperature treatment,P_N,Fv/Fm,?PSII and chlorophyll content of seedlings in non-heading Chinese cabbage were gradually decreased,indicating that high stress might cause the splintering of photosynthetic pigment,reduce the photosynthetic efficiency and inhibit photochemical activity.4.There was substantial accumulation of MDA and H₂O₂ in chloroplast under heat stress.The generation of MDA and ROS were shown to induce membrane lipid peroxidation.The oxidative damage of‘sym'was more serious compared with‘xd'.The seedlings could start their antioxidant system against oxidative stress caused by high temperatures.The heat-tolerant cultivar‘xd'was better at scavenging MDA and ROS,reducing the membrane lipid peroxidation and antioxidant defense capability under heat stress.5.The double membrane system of chloroplast in non-heading Chinese cabbage seedlings was damaged under high temperature,the SL and GL were induced by high temperature to partly loosen and disarranged with numerous osmiophilic plastoglobuli.6.The activity of SS,AI and amylase were decreased under heat stress.the activity of SPS in‘xd'is higher than‘sym'.The conent of soluble sugars,sugar and starch in seedling leaves are remarkable increased,and the increase of‘xd'is more than‘sym'.