Role of chloroplastidial proteases in leaf senescence

Abstract

In this report effect of hydrogen peroxide (H 2O 2) on peroxidase (POD) activity during leaf senescence was studied with and without phenylmethylsulfonyl fluoride (PMSF) pre-treatment in detached neem (Azadirachta indica A. juss) leaf chloroplasts. Increased POD activity was detected in natural and H 2O 2-promoted senescent leaf chloroplasts compared to untreated control mature green leaf chloroplasts. However, under H 2O 2 POD activity markedly increased at 1 day, and then significantly decreased until 4 days. In the presence of H 2O 2, PMSF, the induction of POD activity was alleviated at 1 day, whereas reduced after 4 days. In contrast, in the presence of H 2O 2, cycloheximide (CX), the induction of POD activity was reduced at 1 day, whereas alleviated after 4 days. Partial reduction in H 2O 2-induced POD activity with PMSF and CX, indicating the presence of pre-existing inactive PODs in chloroplasts. We also propose a new role for chloroplastidial proteases as activators of pre-existing inactive PODs during leaf senescence. © 2011 Landes Bioscience.