Extracellular nitric oxide sustains root surface redox activity and growth under sudden flooding-induced hypoxic conditions in barley root tips

Main conclusion Nitric oxide sustains root tip surface redox activity and restricts lipid peroxidation-triggered cell death in the root tips. In order to gain more insight into the involvement of nitric oxide (NO) in plant response to sudden flooding-induced hypoxic stress, we studied the effect of two NO donors, sodium nitroprusside and S-nitroso-L-glutathione, on short-term partial submergence-induced root growth inhibition, alteration in root surface redox activity, lipid peroxidation and cell death in two barley cultivars (cv.) at their early seedling stage. The short-term hypoxic stress induces root growth arrest in cv. Karmel, accompanied by increased lipid peroxidation and cell death. By contrast, in cv. Slaven, short-term hypoxic conditions cause only reduced root growth rate, associated with elevated extracellular NO level in the root tips. The root tip surface redox activity decreases with the increasing timespan of hypoxic conditions in both cultivars; however, this decrease in redox activity started earlier and was greater in the cv. Karmel in comparison with cv. Slaven. Application of NO donors during hypoxic stress sustains the root redox activity and eliminates the hypoxia-induced lipid peroxidation, accompanied by a partial restoration of root growth after short-term hypoxic stress. These results suggest that extracellular NO plays a key role in maintaining the root tip surface redox activity and in the restriction of lipid peroxidation and cell death under short-term hypoxic stress in the root tips of barley seedlings.