Metabolism of hydrogen peroxide during reserve mobilization and programmed cell death of barley (Hordeum vulgare L.) aleurone layer cells

During germination, aleurone layer cells of barley (Hordeum vulgare) grains synthesize and secrete hydrolytic enzymes (principally α-amylase) in response to gibberellic acid (GA); shortly thereafter, the aleurone layer cells undergo programmed death. Gluconeogenesis of lipid reserves within aleurone cells, which supports this hydrolytic enzyme synthesis, results in the generation of H2O2, which is catabolized by glyoxysomal catalase. Lowered amounts of catalase may contribute to aleurone cell death because of a compromised capacity to cope with reactive oxygen species generated by glyoxysomes and mitochondria. In the presence of GA, cells of intact aleurone layers underwent programmed death between 18 and 48 h; in the presence of ABA, no cell death was evident over 60 h. The capacity of GA-treated layers to metabolize exogenous H2O2 increased steadily over the first 24 h, during the stage of lipid mobilization and the major synthesis and secretion of α-amylase; thereafter, this capacity declined markedly. In contrast, cells of ABA-treated aleurone layers exhibited little change in their capacity for H2O2-metabolism. Glyoxysomal catalase increased in activity over the first 12–24 h of GA treatment, which was accompanied by an increase in catalase-1 transcripts between 12 and 18 h. Catalase protein and activity declined after 24 h in GA-treated layers, prior to the onset of rapid programmed death at 30 h. These data suggest that a decline in glyoxysomal catalase precedes death of aleurone cells and may indeed contribute to an increase in cellular oxidative stress.