The role of nitric oxide in the antioxidant defense of plants exposed to UV-B radiation

Abstract

The evidence presented here highlights the role of the nitric oxide (NO) as anti-stress molecule, capable to handling with UV-B-induced changes in the redox state of cell. Our model proposes that the UV-B perception triggers an increase in abscísico acid (ABA) concentration, which increases H2O2 and induces NO. In parallel, UV-B activates the UV-B receptor UVR8. UVR8 is stabilized by endogenous NO and activates the HY5 transcription factor. HY5 may regulate the expression and activity of nitrate reductase, inducing NO increase. NO reduces ROS levels by its scavenger activity. Likewise, HY5 also up-regulates the expression of CHS and CHI. That results in an increase of flavonoid and anthocyanin content, which are capable of absorbing UV-B radiation and scavenge ROS. Moreover, NO may also regulates the activity of the antioxidant system by postranslational modifications of antioxidants enzymes as catalases, peroxidases, oxidases and reductases.