To investigate the physiological mechanisms of salt stress mitigated by exogenous sucrose, Arabidopsis thaliana seedlings grown on Murashige and Skoog medium were treated with 3 % (m/v) sucrose combined with 75, 150, and 225 mM NaCl for 3 d. Our results show that increased salinity significantly decreased the survival rate, fresh mass, content of proteins, chlorophyll a (Chl a), and chlorophyll b (Chl b), and activities of antioxidant enzymes, whereas enhanced the content of malondialdehyde. However, the treatment with sucrose significantly enhanced salt stress tolerance in the Arabidopsis seedlings by decreasing lipid peroxidation and increasing the activities of superoxide dismutase, peroxidase, and catalase, the content of proteins, Chl a, Chl b, anthocyanins, and the transcription of genes involved in anthocyanin biosynthesis. Thus, sucrose might reduce ROS-induced oxidative damage by enhancing activities of antioxidant enzymes and the content of anthocyanins, thereby preventing membrane peroxidation and denaturation of biomolecules.

In this study, we chose apple leaf as plant material and studied effects of GeO 2 on operation of photosynthetic apparatus and antioxidant enzyme activities under strong light. When exogenous GeO 2 concentration was below 5.0 mg L -1 , maximum photochemical quantum yield of PSII and actual quantum yield of PSII photochemistry increased significantly compared with the control under irradiances of 800 and 1,600 μmol(photon) m -2 s -1 . Photosynthetic electron transport chain capacity between Q A -Q B , Q A -PSI acceptor, and Q B -PSI acceptor showed a trend of rising up with 1.0, 2.0, and 5.0 mg(GeO 2 ) L -1 and declining with 10.0 mg(GeO 2 ) L -1 . On the other hand, dissipated energy via both ΔpH and xanthophyll cycle decreased remarkably compared with the control when GeO 2 concentration was below 5.0 mg L -1 . Our results suggested that low concentrations of GeO 2 could alleviate photoinhibition and 5.0 mg(GeO 2 ) L -1 was the most effective. In addition, we found, owing to exogenous GeO 2 treatment, that the main form of this element in apple leaves was organic germanium, which means chemical conversion of germanium happened. The organic germanium might be helpful to allay photoinhibition due to its function of scavenging free radicals and lowering accumulation of reactive oxygen species, which was proven by higher antioxidant enzyme activities.