Photosynthetic Characteristics and Chloroplast Ultrastructure of Transgenic Poplar under NaCl Stress

Our objective was to reveal the relationship between photosynthetic traits and salt tolerance of the AtNHX1 gene transformation into poplar.In order to investigate the effects of salt stress on photosynthetic pigment contents,photosynthetic parameters and chloroplast ultrastructure,wild-type poplar(Populus×euramericana 'Neva',Wt) and transgenic poplar(Tr) were subjected to low salt and high salt treatments.The results showed that,under the salt stress condition,chlorophyll(Chl) contents,Carotenoid(Car) contents,net photosynthetic rate(Pn),transpiration rate(Tr),and stomatal conductance(Gs) of the two strains declined,and all these parameters decreased gradually with the increasing of salt content.However,the decline of Chl,Pn,Tr and Gs was slighter for Tr than for Wt,and the discrepancy was increased with the increasing of salt content.The dynamic changes of Gs,intercellular CO2 concentration(Ci) and stomatal limiting value(Ls) indicated that the decline of Pn was mainly caused by the stomatal limitation under low salt stress,and by both of stomatal and non-stomatal limitation under high salt stress.Under salt stress,the chloroplasts of Wt were shrunken and became round in shape,the internal structure became simplified or disappeared and the plastoglobuli increased significantly,while the chloroplasts of Tr under low salt stress were no different from the control,and the structure of chloroplasts under high salt were better than that of Wt.These indicated that salt stress wrecked the chloroplast structure and induced the decrease of chloroplast contents,moreover,so as to restrain the photosynthetic activity of poplar.The changes of chlorophyll contents,photosynthetic parameters,stomata characters and the ultrastructure of chloroplast correlated significantly to salt tolerance of poplar.Under the same salinity level,the transgenic poplar can maintain a relative integrated chloroplast,high chlorophyll contents and preferable net photosynthetic rate,so its salt tolerance were improved.