The role of antioxidant mechanism in photosynthesis under heavy metals Cd or Zn exposure in tobacco leaves

We examined the effects of Cd and Zn exposure on the photosynthetic function and the tolerant mechanisms of ROS metabolism in tobacco leaves. The results showed that the photosynthesis inhibition caused by Cd exposure was due to the limitation of both stomatal and non-stomatal factors, while Zn exposure only showed a significant effect on the Gs of tobacco leaves. Cd increased the generation rate of O2•– and the content of H2O2, but Zn did not lead to the ROS burst. Cd enhanced the POD activity, but inhibited SOD and CAT activities. The activities of SOD and POD significantly increased under Zn exposure. Cd inhibited the activity and expression of APX. The up regulation of GPX, GR and GST expression and the increase of their activities also play a positive role in the adaptation to Cd. Although Zn inhibited the activities of APX and GPX, it had little effect on other enzyme activities and protein expression in AsA-GSH cycle. TPX and TrxR activities, Trx-Prx pathway-related proteins are very sensitive to Cd. However, only PrxQ and 2-Cys Prx BAS1, which are located in chloroplast, and Trx-HFC164 were significantly down-regulated in Trx-Prx pathway under Zn exposure.