Alleviating Effects Of 6-BA On Sweet Pepper Under High Temperature Stress

Sweet pepper was thermophilic vegetable but unthermostable,and often faced with high temperature stress during the growth and development.Especially in the hot summer months of the south of the Yangtze River in China,early-maturity sweet pepper performed over-summering hardly,and high temperature reduced the yield of sweet pepper.Temperature becomes one of the main ecological factors that effect plant growth and development.In recent years,the "greenhouse effect" and increasing global temperatures continue to rised.Therefore,it's important to improve sweet pepper resistant to heat stress.Firstly,the physiological response of two sweet pepper varieties,a heat-tolerant cultivar and a heat-sensitive cultivar respectively,under high temperature stress was studied.Then,different concentrations of exogenous 6-BA were sprayed on heat-sensitive sweet pepper leaves to investigate the effects of pre-spraying different concentration of 6-BA on sweet pepper under high temperature stress,and selected the best concentration.On this basis,we investigated the alleviating effects of exogenous 6-BA on sweet pepper seedlings by different treating time and different varieties.The major results were as follows:1.Under high temperature stress,MDA content and relative electrolytic leakage increased both in two cultivars,in addition,the MDA content and relative electrolytic leakage of heat-sensitive cultivar P13201 were always higher than these of heat-resistant Yuexia2198;Proline content had a similar result to MDA content,but heat-resistant cultivar was higher significantly than heat-susceptible cultivar,the maximum difference of the two cultivars was appeared at the fifth day under high temperature stress.The activities of SOD and POD showed first increase then decrease,these two indexes,especially POD of heat-tolerant cultivar always higher than these of heat-sensitive cultivar under high temperature stress.2.Different concentrations of exogenous 6-BA?5,10,20,50 ?mol/L?were sprayed on sweet pepper leaves to investigate the effects of 6-BA on the growth and physiological and biochemical indexes of the sweet pepper under high temperature stress.The results showed that 10 ?mol/L of 6-BA was the best relieving concentration for sweet pepper to relieve heat stress.Growth indexes and chlorophyll contents were significantly descended under high temperature stress,while plant height,stem diameter,shoot and root dry matter weight of sweet pepper treated with 10 ?mol/L 6-BA had no significant change compared with the control check?CK?.Contents of chlorophyll a,chlorophyll b and total chlorophyll of sweet pepper treated with10 ?mol/L 6-BA were the smallest among all the treatments;The extent of variation of fluorescence parameters mentioned above in leaves of sweet pepper treated with 10 ?mol/L 6-BA were the lowest among the all treatment groups,especially NPQ,displaying no significance with CK;the productivity of O₂·-,MDA content and relatively conductivity rate in sweet pepper leaves treated with 10?mol/L 6-BA were significantly smaller than those of TO treatment group?distilled water+ high temperature?,the activity of SOD,APX and POD revealed a remarkably increased tendency,namely,to rise by 50.5%,79.4%and 50.3%respectively.In general,10 ?mol/L 6-BA was the best concentration for relieving heat stress,20 ?mol/L 6-BA was followed,5 ?mol/L 6-BA showed few result,while,50 ?mol/L 6-BA increased stress effect instead.3.Two sweet pepper varieties were sprayed 10 ?mol/L 6-BA concentration respactivly.Result showed that plant height,stem diameter,shoot and root fresh matter weight of two sweet pepper varieties,especially heat-sensitive cultivar,had significantly alleviate effect under high temeperature stress.Compared with the control check?CK?,Yield of two sweet pepper cultivars treated with 6-BA of 10 ?mol/L concentration were significantly increased under high temeperature stress,while NPQ were significant decreased.ETR of H-S-W and H-T-W were lower than other treatments under different light intensity,and they reached saturated,even decreased at low light intensity.ETR of two sweet pepper cultivars treated with 10 ?mol/L 6-BA were significant increased,and saturation did not appear at low light intensity.The study indicated that 6-BA could effectively improve the sweet pepper seedlings on light intensity utilization under heat stress,maintaining a normal growth,to alleviate the damage of high temperature stress;two sweet pepper varieties,especially heat-sensitive variety,treated with 10 ?mol/L 6-BA had significant alleviate effect for heat stress4.Contents of chlorophyll a,chlorophyll b and total chlorophyll of Heat+6-BA?treated with 6-BA under high temperature stress?rised by 101.3%,106.9%and 104.2%respectively,compared with the control check?CK?;Fv/Fm?Yield??pPS? were significant increased,NPQ were significant decreased.The treatment which presprayed 6-BA significantly relieved cell membrane-lipid peroxidation,reduced the accumulation of MDA content,thus decreasing the membrane permeability.in addition,the activities of antioxidant enzymes of treatments presprayed 6-BA also increased greatly.The study indicated that 6-BA could promote the synthesis of chlorophyll,alleviated the decomposition of chlorophyll by heat stress to maintaining a normal photosynthetic rates.6-BA could promote energy of light,absorption,energy conversion and electron transfer so that light use efficiency significantly increased.6-BA increased the activities of antioxidant enzymes to alleviate cell membrane-lipid peroxidation,decreased the production of O₂·-and the accumulation of MDA content.