Expression of senescence-enhanced genes in response to oxidative stress.

Expression of the LSC54 gene, encoding a metallothionein protein, has been shown previously to increase during leaf senescence and cell death. Evidence is presented in this paper to indicate that the extent of LSC54 expression is related to levels of oxidative stress in the tissues. Treatment of Arabidopsis cotyledon and leaf tissues with the catalase inhibitor, 3-amino-1,2,4-triazole, or with silver nitrate result in the enhanced expression of LSC54. Combined treatments with quenchers of reactive oxygen species (ROS), such as ascorbate, tiron and benzoic acid indicated that this induced expression was due to increased levels of ROS. The expression of many other senescence-enhanced genes was also found to be inducible by the increase in ROS. Treatment of plant tissue with 3-amino-1,2,4-triazole, followed by silver nitrate, resulted in protection from the severe damage caused by the silver nitrate treatment and reduced expression of many of the genes examined. However, one gene, encoding a lipid hydroperoxide-dependent glutathione peroxidase, showed increased expression in the protected tissue, which may indicate a role for this enzyme in the protection of plant tissue from oxidative stress. ROS-enhanced expression of at least one of the genes investigated required the presence of the salicylic acid signalling pathway, which was not required for the expression of LSC54.