Effects Of Water Stress On The Physiology And Main Secondary Metabolites Of Tetrastigma Hemsleyanum Diels Et Gilg

This study focused on the effects of water stress on the growth and metabolism of Tetrastigma hemsleyanum Diels et Gilg(T.hemsleyanum).The drought resistance and flood tolerance were studied based on the different soil water content.Two-year-old seedlings of T.hemsleyanum were used as materials,and all experiments were conducted in greenhouse.The physiological characteristics and the accumulation of secondary metabolites of T.hemsleyanum under different soil water conditions were investigated by analyzing the morphological structure,physiological indicators and Key enzymes of T.hemsleyanum under different soil water gradients.The study is of great significance for the protection of wild resources,the improvement of the level of artificial domestication and cultivation,and the quality of medicinal materials of T.hemsleyanum.The following results were obtained.(1)Divided into 4 treatment groups,and the soil relative water content were 25%(P1),50%(P2),75%(P3)and 100%(P4).The result shows the content of photosynthetic pigments(Chl a,Chl b,Car)in leaves of T.hemsleyanum showed a decreasing trend.In the group P1,the net photosynthetic rate(Pn),stomatal conductance(Gs),transpiration rate(Tr)decreased continuously,and the intercellular carbon dioxide concentration(Ci)firstly decreased and then increased.But the Photosynthesis indicators of group P4 were first increased and then decreased.In terms of fluorescence parameters,the maximum photochemical efficiency(Fv/Fm)of PSII and the potential activity(Fv/Fo)of PSII in the treatment group with high relative water content and low water content were continuously reduced,and the actual efficiency of photochemical reaction in PSII reaction center(Y(?)),the apparent electron transfer rate(ETR)and the photochemical quenching coefficient(qP)were decreased after an initial increase,while the non-photochemical quenching coefficient(NPQ)increased continuously.(2)The result shows the physiological indexes of group P2 and P3 showed no obvious changes.The physiological indexes of group P1 and P4 changed significantly,the cell membrane permeability,MDA,soluble sugar,soluble protein and proline were significantly higher than those of the group P2 and P3.Moreover,the activities of SOD,POD,CAT firstly increased and then decreased with significant difference,and the content of flavonoids and polyphenols was also significantly higher.However,the content of polysaccharide was significantly lower.In addition,the results showed that the cell membrane permeability and the content of MDA in the group P1 were significantly higher,the activities of SOD,POD,CAT were increased more obviously and with significantly higher content of the osmotic adjustment substance in the group P1.The content of flavonoids and polysaccharides in the group PI was significantly higher than that in the group P4,but the content of polyphenol of the group P4 was significantly higher than that in the group P1.(3)Three treatments were set up,separately named the drought group(always no watering),the control group(normal watering)and the flooded group(water submerged underground part).The result shows that the water stress no matter drought stress or flood stress caused the ultrastructural changes of chloroplast in T.hemsleyanum.The number of chloroplasts decreased,and they moved toward the center of the cell instead of clinging to the cell wall.Besides,the number of plastid globules in the chloroplast increased and the volume became larger,the color is lighter,and the lamella structure in the chloroplast is no longer neat and compact;Interestingly,water stress no matter drought stress or flood stress resulted in high accumulation of flavonoids.Analysis of enzyme activities of key enzymes in the biosynthetic pathway of flavonoids showed that the activities of phenylalanine ammonia-lyase,chalcone synthase and chalcone isomerase increased successively,by analyzing the correlation between flavonoids and PAL,CHS,CHI,it can be found that water stress enhances the correlation between them.To sum up,T.hemsleyanum adapted to environmental changes by regulating stress resistance physiological indicators and metabolites under water stress.Moderate water stress is beneficial to the accumulation of active components such as flavonoids of T.hemsleyanum.