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Palma K, Kermode AR: Metabolism of hydrogen peroxide during reserve mobilization and programmed cell death of barley (Hordeum vulgare L.) aleurone layer cells. Free Radic Biol Med. 2003 Nov 15;35(10):1261-70.
During germination, aleurone layer cells of barley (Hordeum vulgare) grains synthesize and secrete hydrolytic enzymes (principally alpha-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 H (2) O (2), 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 H (2) O (2) increased steadily over the first 24 h, during the stage of lipid mobilization and the major synthesis and secretion of alpha-amylase; thereafter, this capacity declined markedly. In contrast, cells of ABA-treated aleurone layers exhibited little change in their capacity for H (2) O (2)-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. |
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