Expression analysis of genes related to oxidativeprotection during senescence in Brassica napus

Leaf senescence is the sequence of events leading to cellular disassembly and mobilization of released materials that cause accumulation of reactive oxygen species. DNA sequencing of one of senescence-isolated cDNA, LSC650, showed a high level of similarity with a catalase gene of Arabidopsis. Transcript level of this isoform was highly increased during senescence. The enzyme activity of catalase was also assayed during different developmental stages in Brassica napus and showed a high level of activity during last part of leaf senescence. Both kinetic assay and northern analysis exhibit that catalase has the potential to play a significant role in the cell defense against produced hydrogen peroxide as part of the macromolecules breakdown. Gene expression pattern was characterized by mRNA hybridization with several antioxidant cDNA clones. Transcript levels of discussed genes were markedly increased during senescence stages. We conclude that the major part of the mRNA changes observed during senescence stages of leaves is connected with leaf senescence, whereas free radical-related transcripts appear to protect cells from oxidative damage.