Photosynthetic Characteristics and Antioxidative Responses in Three Species of Crassulaceae Following Drought Stress

Photosynthetic characteristics and induction of crassulacean acid metabolism (CAM) by drought stress were investigated in Sedum album, Sedum stoloniferum and Rosularia elymaitica from Crassulaceae. Titratable acidity, malate content, phosphoenolpyruvate carboxylase (PEPC) activity and gas exchange parameters were determined in plants at the end and beginning of the photoperiod. Results showed that, significant changes in dusk/dawn titratable acidity (?Acidity) and malate (?Malate) could be detected in all three studied species after 20 days drought stress. However, ?acidity and ?malate in leaves of Sedum stoloniferum and R. elymaitica were less than values obtained for S. album. Although drought stress caused a significant increase in the activity of PEPC in all three studied species, difference between daytime and nighttime PEPC activity was significant only in S. album. In S. stoloniferum and R. elymaitica, despite of an increase by drought stress, net nighttime CO2 assimilation was still negative resembling a C3-like pattern of gas exchange. Comparison of responses of S. album with other two tested species showed that, drought stressed S. stoloniferum and R. elymaitica develop a low degree of CAM activity e.g. CAM-cycling metabolism, while S. album is capable to exhibit a typical CAM pathway under drought stress e.g. C3-CAM intermediate. Activity of superoxide dismutase and catalase were decreased under drought stress, but that of peroxidase and ascorbate peroxidase did not change. The exception was an increase in peroxidase activity in drought stressed R. elymaitica, suggesting an important role for this enzyme in the protection against ROS in this species.