Study On Physiological And Biochemical Mechanisms Of Drought Resistance In Grape Under Simulated Drought Stress

A year-old drought-resistant rootstock "Beida" and main fresh grape varieties"Xiahei"," Heibaladuo " and "Chenxiang" in Western Inner Mongolia were used as materials in the experiment.PEG-6000 with 15%concentration was used to simulate drought stress.Physiological and biochemical indexes of leaves of four grape varieties were measured at 0 h(CK),24 h,48 h,72 h and 96 h,in order to explore the changes of these indexes in response to drought.And used subordinate function values to evaluate the drought resistance of four grape varieties.The experimental results are as follows:1.With the deepening of drought stress,the leaf water content of four varieties showed a downward trend.The leaf water content of "Beida" was always higher than that of the other three varieties in the whole process of drought stress,and the decrease of leaf water content was the smallest,followed by "Chenxiang",which had a higher leaf water content and a smaller decline in the process of drought,and also showed a better water-holding capacity.In the process of drought,the lowest level of leaf water content and the greatest decline is "Xiahei",which is the most affected by drought among the four varieties and the weakest water-holding capacity.2.The electrical conductivity of four varieties showed an upward trend with the increase of drought stress.Among them,the electric conductivity of "Beida" and"Chenxiang”changed slightly.The order of the specific electric conductivity was"Xiahe">" Heibaladuo ">"Chenxiang">"Beida",and the electrical conductivity of"Beida" and "Chenxiang" also maintained a low level,indicating that the cell membrane system of "Chenxiang" and "Chenxiang" was damaged relatively less by drought,with less extravasation of substances,showing strong drought resistance.3.Under drought stress,photosynthetic pigments:chlorophyll a,chlorophyll b and carotenoid contents of four varieties showed a downward trend.The order of chlorophyll and carotenoid contents of four varieties in the whole process was"Beida">"Chenxiangn>""Heibaladuo">"Xia Hei".Even though "Beida" sometimes declined a little more,it remained the highest in terms of total chlorophyll content and carotenoid content,"Beida" have more photosynthesis than other varieties.The photosynthetic pigments level of drought-resistant varieties would be higher.With the deepening of drought stress,the photosynthetic parameters,net photosynthetic rate(Pn),stomatal conductance(Gs)and transpiration rate(Tr)of the four varieties showed a downward trend with different ranges of change.The net photosynthetic rates of "Beida" and "Chenxiang" were higher,while stomatal conductance and transpiration rate were lower.This indicated that the photosynthetic rates of "Beida"and "Chenxiang" were higher than those of ""Heibaladuo " and "Xiahei",Water conservation capacity of "Beida" and "Chenxiang" is also strong in drought conditions.At the same time,intercellular CO2 of four varieties decreased first and then increased with drought stress because of stomatal and non-stomatal limitations.4.With the deepening of drought stress,the UWL of four varieties showed a gradual downward trend,while that of the drought-resistant varieties had the smallest decline.In the whole process of stress,the UWL of "Beida" was always at the highest level.The specific order was"Beida">"Chenxiang">"Heibaladuo">"Xiahe".And UWL was positively correlated with net photosynthetic rate(Pn),transpiration rate(Tr),stomatal conductance(Gs),chlorophyll content,and UWL was significantly correlated with photosynthesis.5.Superoxide dismutase(SOD),peroxidase(POD)and catalase(CAT)in the antioxidant enzyme system of four varieties increased first and then decreased with the deepening of drought stress.Under severe drought,the three enzymes showed a downward trend,indicating that the regulation of antioxidant enzymes to drought was not unlimited.At the same time,POD,SOD and CAT of "Beida" and "Chenxiang"increased more rapidly than those of " Heibaladuo " and " Xiahe "when drought aggravated,and they also maintained a higher level of enzyme activity.Membrane lipid peroxidation take place in cell membrane system under drought,the final product of accumulation is malondialdehyde(MDA).MDA content of four grapes showed an upward trend with the deepening of drought stress,the order of MDA content was"Xiahei","Heibaladuo ","Chenxiang","Beida",and the MDA content of"Beida" was much lower than that of the other three varieties,showing strong drought resistance.6.The osmotic adjustment substances of soluble sugar,soluble protein and free proline in four varieties were studied.With the deepening of drought stress,the soluble sugar content of four grape varieties increased first and then decreased,and the free proline showed a sustained upward trend,and the soluble protein also showed a sustained upward trend.Under mild drought stress,the increase of soluble sugar in"Beida" was similar to that in "Chenxiang","Black Barbado" and "Xiahei",however,under severe drought stress,the increase of soluble sugar in "Beida" increased significantly,followed by "Chenxiang"," Heibaladuo "and "Xiahei" grew relatively slowly.The soluble protein and free proline of "Beida" kept the highest level during the whole stress process.The order of the other three varieties was " Chenxiang ","Heibaladuo","Xiahei ".The osmotic regulation of "Beida" and " Chenxiang" were still better.7.With the aggravation of drought stress,the ABA content of four varieties showed an upward trend,and BR showed a trend of first increasing and then decreasing.The content of ABA and BR in the drought-resistant varieties "Beida"changed slightly,tended to maintain the stable state of hormones,and the content of hormones in the drought-resistant cultivar "Xiahei" changed greatly.8.The drought resistance of four grapes was evaluated by subordinate function values.The order of drought resistance of four grapes was "Beida">"Chenxiang">"Heibaladuo ">"Xiahe".