RESPONSES OF THE CHLOROPLASTIC ANTIOXIDANT SYSTEM OF Hedysarum Mongolicum AND Caragana Korshinskii TO INCREASING DROUGHT STRESS AND THEIR EFFECTS ON THE PHOTOSYNTHESIS

摘要

To investigate the effects of increasing drought on the photosynthesis of xerophytic shrubs,a water-controlled pot culture of Hedysarum mongolicum and Caragana korshinski, two commonly planted shrubs in the arid regions in northwest China, was conducted. The shrubs were planted in light, moder-ate and serious drought treated soils (LD. MD and SD, the soil moistures are 65%,50% and 30%of the field capacity, while the common soil moisture is 75% of that). The responses of the chloroplastic an-tioxidant system, photosynthetic response parame-ters and the relationships among them were detected. The results indicated that(1)the chloroplastic ascor-bate peroxidase(APX)and dehydroascorbic acid re-ductase (DHAR)activities of H. mongolicum signif-icantly increased in LD conditions, while the gluta-thione reductase(GR) activity significantly de-creased. Chloroplastic superoxide dismutase(SOD), DHAR and GR activities of C.korshinskii and anti-oxidants contents (ascorbic acid, glutathione and ca-rotenoids)significantly increased in LD conditions. Along with the increasing drought stress, chloro-plastic antioxidase activities and antioxidants con-tents in both shrubs exhibited increasing tendencies, except for the APX and GR activities of C. korshin-skii and the DHAR activities of both the shrubs, which exhibited significant decreases after tempo-rary increasing. Significant chloroplastic membrane lipid peroxidationstarted to be observed in SD and LD conditions for the 2 species, respectively.(2) the maximum net photosynthetic rate(Pmmax), light satu-ration point(LSP), the maximum carboxylation rate was (Vcmax), the maximum electron transfer rate (Jmax)and the utilization rate of triose phosphate (TPU)of H. mongolicum and the Pmax,apparent quantum efficiency(AQY), Jmax and TPU of C. korshinski significantly decreased in LD conditions. Along with the increasing drought stress,all the pho-tosynthetic response parameters except dark respira-tion rate(Ra)and light compensation point(LCP)ex-hibited decreasing tendencies.(3)there were signif-icant negative relationships among parts of the chlo-roplastic antioxidant indices and photosynthetic re-sponse parameters, however, the oxidative damage of chloroplasts is not the only dominant limiting fac-tor of the photosynthesis under drought stress.(4)H. mongolicum was more suitable for the revegetation of arid regions in LD and MD conditions than C. korshinskii considering their abilities of chloro-plastic antioxidation and maintaining photosynthesis.