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Nitric oxide (NO) has been shown to be involved in diverse physiological processes in microbes, animals and plants. In this study, the involvement of NO in the development and possible roles in oxidative stress protection of Chinese cabbage (Brassica rapa subsp. pekinensis cv. Samrack-ulgari) seedlings were investigated. Exogenous application of sodium nitroprusside (SNP) retarded root elongation, while increasing lateral root formation of Chinese cabbage. Plants showed no signs of external stress due to SNP application in true leaves. Cotyledons of 3-week-old Chinese cabbage plants were found to be highly sensitive to SNP application. Treated cotyledons displayed rapid tissue collapse and associated cell death. Although SNP application reduced root growth under normal growth conditions, it also enhanced methyl viologen (MV)-mediated oxidative stress tolerance. Analysis of SNP application to Chinese cabbage leaf disks, revealed SNP-induced tolerance against oxidative stresses by MV and H 2 O 2 , and evidence includes prevention of chlorophyll loss, superoxide anion (O 2 -) accumulation and lipid peroxidation. This report supports a role for nitric oxide in modulating early seedling development, programmed cell death and stress tolerance in Chinese cabbage. KeywordsChinese cabbage Á Nitric oxide Á Oxidative stress Á Root development Abbreviations DAB 3,3 0 -Diaminobenzidine MV Methyl viologen NBT Nitro blue tetrazolium NO Nitric oxide PCD Programmed cell death RNS Reactive nitrogen species ROS Reactive oxygen species SNP Sodium nitroprusside

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