Antioxidative system’s responses in the leaves of six Caragana species during drought stress and recovery

For investigating the protective roles of antioxidative system in desiccation tolerance of Caragana species as they adapt to arid environments, we monitored a variety of ecophysiological parameters in the leaves of Caragana arborescens (mesophyte), C. microphylla (semiarid species), C. roborovskyi, C. stenophylla, C. acanthophylla, and C.tragacanthoides (xerophyte) grown under a drying-rehydration cycle. Relative leaf water content and chlorophyll content were decreased by 17.4–39.2 %, and by 14–40 %, respectively, after exposure to 48 days of drought stress. Malondialdehyde did not increase in xeric Caragana species. Hydrogen peroxide concentrations increased by 13.1–43.9 % except in C. acanthophylla. The activities of superoxide dismutase (SOD), guaiacol peroxidase (POD), ascorbate peroxidase (APX), glutathione reductase (GR) and reduced glutathione (GSH) in xeric Caragana species were significantly elevated with progressing drought stress. However, catalase in all species decreased markedly before drought stress treatment reached 40 days. The xeric Caragana species showed higher SOD, POD, APX, and GR activities, as well as ascorbate content, and more manganese SOD isoenzymes. C. arborescens and C. microphylla accumulated more free proline. Our data indicate that SOD and POD with the ascorbate–glutathione cycle have important protective effects in xeric Caragana species under drought stress. Free proline may be crucial in the resistance of C. arborescens and C. microphylla to drought stress.