Role of salicylic acid in alleviating photochemical damage and autophagic cell death induction of cadmium stress in Arabidopsis thaliana

As a widespread pollutant in the environment, cadmium (Cd) would be accumulated in leaves and cause phytotoxic effect on plants. Salicylic acid (SA), a natural signal molecule, plays an important role in eliciting specific responses to biotic and abiotic stresses. In our case, the effect of SA on Cd-induced photochemical damage and cell death in Arabidopsis was studied. The results illustrated that Cd could cause a series of physiological events such as chloroplast structure change (e.g. irregular mesophyll cell as well as ultrastructure change), reactive oxygen species (ROS) production and cell death. Furthermore, chlorophyll fluorescence parameters (Fv/Fm, qN and ETR) showed a rapid decrease in wild-type (WT) Arabidopsis after treatment with 50 µM CdCl2, identical with the change in chlorophyll delayed fluorescence (DF) intensity. The changes of these parameters showed the damage of Cd toxicity to photosynthetic apparatus. We found that cell death might be autophagic cell death, which might be caused by Cd toxicity induced oxidative stress just like photosynthetic damage. The NahG plants with lower SA accumulation level showed more sensitivity to Cd toxicity, although they exhibited a decrease both in chlorophyll fluorescence parameters and DF intensity. Exogenously SA prevented the Cd-induced photochemical efficiency decrease and mitigated Cd toxicity. Additionally, SA pretreatment could alleviate Cd-induced ROS overproduction. In conclusion, our results suggested that SA could prevent Cd-induced photosynthetic damage and cell death, which might be due to the inhibition of ROS overproduction.