SNF1-related protein kinases type 2 are involved in plant responses to cadmium stress

Abstract

Cadmium ions are notorious environmental pollutants. In order to adapt to cadmium-induced deleterious effects plants have developed sophisticated defense mechanisms. However, the signaling pathways underlying the plant response to cadmium are still elusive. Our data demonstrate that SNF1-related protein kinases 2 (SnRK2s) are transiently activated during cadmium exposure and are involved in the regulation of plant response to this stress. Analysis of Nicotiana tabacum Osmotic Stress-Activated Protein Kinase (NtOSAK) activity in tobacco BY-2 cells indicates that reactive oxygen species (ROS) and nitric oxide, produced mainly via an L-arginine-dependent process, contribute to the kinase activation in response to cadmium. SnRK2.4 is the closest homologue of NtOSAK in Arabidopsis thaliana. Comparative analysis of seedling growth of snrk2.4 knockout mutants versus wild type Arabidopsis suggests that SnRK2.4 is involved in the inhibition of root growth triggered by cadmium; the mutants were more tolerant to the stress. Measurements of the level of three major species of phytochelatins in roots of plants exposed to Cd2+ showed a similar (PC2, PC4) or lower (PC3) concentration in snrk2.4 mutants in comparison to wild type plants. These results indicate that the enhanced tolerance of the mutants does not result from a difference in the phytochelatins level. Additionally, we have analyzed ROS accumulation in roots subjected to Cd2+ treatment. Our data show significantly lower Cd2+-induced ROS accumulation in the mutants’ roots. Concluding, the obtained results indicate that SnRK2s play a role in the regulation of plant tolerance to cadmium, most probably by controlling ROS accumulation triggered by cadmium ions.