Document Type : Research Paper
Department of Agricultural Biotechnology, Faculty of Agriculture, Imam Khomeiny International University, Qazvin, I.R. Iran.
Department of Plant Genetics and Biotechnology, Horticulture Research International, Wellesbourne, Warwick, England, CV34 9EF.
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 radicalrelated transcripts appear to protect cells from oxidative