H2O2 production and gene expression of antioxidant enzymes in kimchi cabbage (Brassica rapa var. glabra Regel) seedlings regulated by plant development and nitrosative stress-triggered cell death

Abstract

Two different growth stages of 12-day-old and 28-day-old kimchi cabbage seedlings showed differential chlorophylls, ion leakage, nitric oxide (NO) and H2O2 productions in their cotyledons and true leaves under normal growing conditions. Gene expression of various antioxidant enzymes such as superoxide dismutase, catalase, ascorbate peroxidase (APX), monodehydroascorbate reductase, dehydroascorbate reductase, glutathione reductase 1 (GR1) and glutathione S-transferase 1 (GST1) was also regulated in the growth stage- and the leaf position-dependent manners at the two growth stages of the seedlings. Sodium nitroprusside (SNP) NO donor (0.5 mM) caused tissue damage in cotyledons of the seedlings but not in true leaves. Differential NO and H2O2 were accumulated in the cotyledons and the true leaves with and without SNP application. Cat1, APX and GST1 were induced in the cotyledons by 0.5 mM of SNP at 6 h. GST1 gene was inducible in the cotyledons at 6 and 24 h, as well as in the true leaves by the SNP at 24 h. Increasing SNP doses more than 10 mM caused distinct increase in cellular damages of true leaves. Endogenous NO and H2O2 contents were inversely modulated by applied SNP showing NO increase and H2O2 decrease in the true leaves at 6 h. The nitrosative stress-triggered cell death augmented transcription of Cat1, APX, GR1 and GST1 genes, but down-regulated Cat2 gene expression in the true leaves at 6 h. Taken together, transcriptional regulation of antioxidant enzymes might be one of the mechanisms involved in H2O2 decomposition and glutathione-dependent defenses during the seedling development and nitrosative stress tolerance in the kimchi cabbage plants.