Changes Of Flavonoids In Zelkova Schneideriana Of Different Autumn Leaf Colors And Their Responses To Drought Stress

The relationship between plant secondary metabolism and stress resistance has been a hot topic in recent years,as flavonoids are important antioxidant substances in plants,they play a key role in eliminating and alleviating active oxygen damage caused by drought and other stresses.However,compared with other adversities,drought is one of the common stresses of garden plants.In order to clarify the relationship between leaf color changeand flavonoid content of Zelkova schneiderianaand the effect of drought stress on flavonoid content,three one-year-oldgrafted Z.schneideriana seedlings with different leaf colours in autumn were used as materials.The optimum extraction conditions of flavonoids from Z.schneideriana leaves were determined by the experiment design which combined single factor with response surface,the content of three flavonoids in Z.schneideriana was measured by high performance liquid chromatography(HPLC),and the changes of total flavonoids,phenylalanine ammonia lyase(PAL),chalcone isomerase(CHI),rutin,quercetin and catechin in flavonoid metabolic pathways of Z.schneideriana under drought stress were determined by controlling water in pots and setting different degrees.Finally,through correlation analysis and principal component analysis,the change characteristics of six substances in three Z.schneiderianawith different leaf colours in autumn and their relationship with drought stress gradient were established,and the response between flavonoid metabolism and drought stress was understood.Main results of this study are as follows:1.The optimum conditions for ultrasound extracting flavonoids from Z.schneideriana leaves were as follows:ethanol volume fraction 63%,liquid-solid ratio 31:1(mL/g),extraction time 1.7 h.2.The content of catechin,rutin and quercetin in Z.schneideriana leaves was determined by high performance liquid chromatography(HPLC).In three Z.schneideriana with red,yellow and greenleaves in autumn,the content of catechin was the highest,rutin was the second and quercetin was the lowest.Moreover,catechin and rutin were the highest in yellow,while quercetin was not significantly different in red,yellow and green.3.During the period of Z.schneideriana leaf color change,the trend of six substances in flavonoid metabolic pathways inthree Z.schneideriana were as follows:PAL activity,CHI activity and total flavone content increased with time,while quercetin content decreased with time.Rutin and catechin contents varied with time in three Z.schneideriana.Significance analysis of six substances in leaves of three Z.schneideriana was carried out:PAL activity,rutin content and catechin content in the yellow were significantly higher than other two,while CHI activity,total flavonoid content and quercetin content were not significantly different among the three Z.schneideriana.4.Under drought stress,PAL activity and CHI activity of three Z.schneideriana were increased,which were positively correlated with the degree of drought stress and cumulative stress time.The content of quercetin and catechin decreased,which was negatively correlated with the degree of drought stress and cumulative stress time.The contents of total flavonoids and rutin increased first and then decreased with the prolongation of stress time.What's more,under different drought stress,the accumulation of total flavonoids in Z.schneideriana of different autumn-leaf was different.Severe drought is more conducive to the accumulation of total flavonoids in red and green,while mild drought is more conducive to the yellow.Besides,different degrees of drought stress have different effects on rutin accumulation.Mild,moderate and severe drought stress was not conducive to the accumulation of Rutin in yellow,but was conducive to the accumulation of Rutin in red and green.Under moderate drought,the rutin accumulation of red was the largest,while that of green was the largest under mild drought.5.The correlation analysis of six substancesin flavonoid metabolism showed that:the total flavonoid content in Z.schneideriana leaves was positively correlated with PAL activity,CHI activity and rutin content,negatively correlated with quercetin content and catechin content.There was no significant correlation between rutin content and CHI activity,quercetin content and catechin content.6.Principal Component Analysis showed that this six substances could be divided into two categories:total flavonoids,PAL,CHI,quercetin and catechin as the first principal component and rutin as the second principal component.These two principal components contain all the indicators determined,indicating that this six indicators related to flavonoid metabolism in Z.schneideriana under drought stress are closely related to the flavonoid metabolism.7.According to the membership function value and comprehensive index of flavonoid-related substances of three experimental materials,the drought resistance of three autumn-leaf Z.schneideriana was ranked as red>yellow>green.