Effects Of UV-B Acclimation On Cold Tolerance Of Eucommia Ulmoides Oliv.

Eucommia ulmoides Oliv.(EUO)is a unique multi-purpose economic tree species in China.It is great practical significance to study the cultivation of strong seedlings of EUO In this study,three-year-old EUO seedlings as the research object,the effects of UV-B acclimation on photosynthetic growth index,osmotic adjustment substance content,antioxidant enzyme activity,lipid peroxidation and primary metabolism in EUO were analyzed under low temperature stress,the physiological mechanism of the effects under UV-B acclimation on the ability of EUO to resist low temperatures was investigated.The results were as follows:(1)During UV-B acclimation,the leaf biomass,net photosynthetic rate,stomatal conductance,transpiration rate and total soluble sugar content decreased significantly in the acclimated plants,the contents of superoxide anion,malondialdehyde(MDA),total phenol,total flavonoids,proline and soluble protein increased significantly,and the activities of SOD,POD,CAT increased significantly,there were 37 primary metabolites with significant differences by GC-MS analysis,they were mainly concentrated in the metabolism of citrate cycle,Alanine,aspartate and glutamate metabolism,glyoxylate and dicarboxylate metabolism.(2)At the end of acclimation recovery,the leaf area,leaf thickness,net photosynthetic rate,photosynthetic pigment content,total phenol content,total flavone content and salicylic acid content of plants increased significantly in EUO from moderate and low intensity acclimation groups,the activities of SOD and POD were significantly increased,the contents of superoxide anion and MDA,and the heat loss were significantly decreased.The net photosynthetic rate was significantly increased in EUO from the acclimation group of UV-B under low temperatures stress,osmotic adjustment substance content,antioxidant enzyme activity,antioxidant substance content,superoxide anion,MDA content significantly decreased,there were 43 different primary metabolites,which were mainly concentrated in butyric acid metabolism pathway,pyruvate metabolism,glyoxylate and dicarboxylate metabolism,galactose metabolism.(3)Correlation analysis showed that galactose metabolism was positively correlated with EUO height,soluble total sugar content,soluble protein content,proline content and superoxide anion content,and there was negatively correlated between galactose metabolism and net photosynthetic rate,the content of total flavonoids.The ability to resist low temperatures in EUO from UV-B acclimation group was higher than that of the control by the principal components and factor analysis,The salicylic acid content from moderate and high intensity UV-B acclimation group was the key factor against low temperature stress,POD activity from low intensity UV-B acclimated group was the key factor against low temperature stress.(4)The plants from moderate intensity UV-B(2.8 kJ·m-2·d-1)acclimation group had the strongest ability to resist low temperature stress,the ability to resist low temperature was enhanced mainly through increasing photosynthesis,and then affecting sugar metabolism,organic acid metabolism and other metabolic pathways.The contents of soluble total sugar,proline and salicylic acid were increased,POD activity was increased,and the degree of peroxidation was decreased.