Spermidine Enhances Waterlogging Tolerance via Regulation of Antioxidant Defence, Heat Shock Protein Expression and Plasma Membrane H+-ATPase Activity in Zea mays

Polyamines (PAs) are ubiquitous biogenic amines that play important roles in the environmental stress tolerance of crops. However, the relationship between PAs and plant waterlogging (WL) tolerance has received little attention. In this study, the protective effects of spermidine (Spd) against WL stress were investigated by Zea mays. WL treatment inhibited root growth and caused a significant increase in lipid peroxidation, membrane permeability and DNA damage in maize roots. Pre-soaking seeds with Spd markedly alleviated these effects caused by WL. Spd pre-soaking also significantly increased the endogenous Spd content in both control and waterlogged maize roots. In addition, the activity of antioxidant enzymes (catalase, CAT; glutathione reductase, GR; superoxide dismutase, SOD; peroxidase, POD) was enhanced in Spd-pre-soaked maize roots under WL stress. Thus, hydrogen peroxide (H2O2) and superoxide-radical (O2 center dot-) accumulation were reduced. Spd treatment also enhances the expression and protein abundance of heat shock protein (HSP) 70 and 90 during the period of WL stress. Furthermore, Spd pre-soaking reversed the inhibition effect of WL on H+ efflux and K+ influx in maize roots. The PM H+-ATPase activity in Spd-pre-treated seedlings exhibited less inhibitory under WL conditions. In conclusion, this study suggests that WL stress could be alleviated by priming seeds with Spd in maize species. This alleviative effect was partially attributable to (i) up-regulated activity of antioxidant enzymes; (ii) maintained PM H+-ATPase activity; and (iii) increased Hsp70 and Hsp90 gene expression and protein abundance.