Physiological responses to nitrate stress of transgenic tobacco plants harbouring the cucumber mitogen-activated protein kinase gene

The physiological responses to nitrate stress of 2 transgenic tobacco lines containing the cucumber mitogen-activated protein kinase (CsNMAPK) gene were investigated. Seed germination rates of the transgenic tobacco lines were higher than that of the wild type (WT) tobacco under 150 mM nitrate treatment. The transgenic seedlings had higher root fresh weight (FW) and dry weight (DW) than the WT plants after 98 mM and 182 mM nitrate treatment. The malondialdehyde (MDA) content, electrolytic leakage (EL), and H2O2 content were higher in the WT than they were in the transgenic plants after 7-day nitrate stress treatment. The antioxidant enzyme (superoxide dismutase [SOD], catalase [CAT], peroxidase [POD], ascorbate peroxidase [APX]) activities increased with the increasing of nitrate concentration and the transgenic plants exhibited higher activities than the WT did. Excess nitrate stress induced more proline accumulation in the transgenic plants than in the WT plants. These results suggested that the tolerance of overexpressing-CsNMAPK tobacco plants to nitrate stress might partly be attributed to higher antioxidant enzyme activities and enhanced osmotic regulation capacity.