The role of SIPK signaling pathway in antioxidant activity and programmed cell death of tobacco cells after exposure to cadmium.

Cadmium (Cd) toxicity induces oxidative burst and leads to programmed cell death (PCD) in plant cells. The role of salicylic acid-induced protein kinase (SIPK) signaling pathway in Cd-induced oxidative stress was investigated in suspension-cultured tobacco (Nicotiana tabacum L. cv. Barley 21). The cells were pretreated with 40 μM PD98059 (inhibitor of MAPKK) and then exposed to 50 μM Cd for 24 h. The percentages of cell viability, apoptosis, necrosis, and the content of reactive oxygen species (ROS) were monitored by flow cytometry. Expression of PCD related gene (Hsr203J) and the contents of certain signaling molecules were measured as well. The results showed that Cd increased the expression of SIPK, Hsr203J, and CAT genes, the activities of catalase and caspase-3-like enzymes. Addition of PD98059 inhibitor reduced the expression of Hsr203J and CAT genes, decreased CAT activity, but increased ROS and SA contents, and caspase-3-like activity and apoptosis rate. The highest apoptosis level was accompanied by the highest level of Hsr203J gene expression. From the results it can be suggested that upon treatment of tobacco cells with Cd, internal SA content increased and induced the SIPK signaling pathway, thereby inhibited the antioxidant system and led to PCD.