Relationship between polyamines conjugated to mitochondrion membrane and mitochondrion conformation from developing wheat embryos under drought stress

The mitochondrion conformation and the contents of conjugated polyamines were investigated using the embryos of developing wheat (Triticum aestivum L.) grains of two cultivars differing in drought tolerance as experiment materials. After drought stress treatment for 7 days, the relative water content of embryo and relative increase rate of embryo dry weight of the drought-sensitive Yangmai No. 9 cv. decreased more significantly than those of the drought-tolerant Yumai No. 18 cv. Furthermore, the changes in mitochondrion conformation of Yangmai No. 9 were more marked. Meanwhile, the increases of the contents of conjugated non-covalently spermidine (CNC-Spd) and conjugated covalently putrescine (CC-Put) of Yumai No. 18 were more obvious than those of Yangmai No. 9. Treatment with exogenous Spd not only alleviated the injury of drought stress to Yangmai No. 9, but also enhanced the increase of CNC-Spd content and inhibited the change in the mitochondrion conformation of this cultivar. The treatments of Yumai No. 18 with two inhibitors, methylglyoxyl-bis (guanylhydrazone) and phenanthrolin, significantly inhibited the drought stress-induced increases of CNC-Spd and CC-Put contents of the cultivar, respectively. Meanwhile, the treatments with the two inhibitors aggravated the injury of drought stress to Yumai No. 18 and enhanced the change in the mitochondrion conformation of this cultivar. These results mentioned above suggested that the CNC-Spd and CC-Put in embryo mitochondrion membrane isolated from developing grains could enhance the wheat tolerance to drought stress by maintaining the mitochondrion conformation.

Involvement of putrescine in osmotic stress-induced ABA signaling in leaves of wheat seedlings

To elucidate one mechanism by which putrescine (Put) functions in plant signaling under osmotic stress, Put and ABA contents, and plasma membrane-NADPH oxidase (PM-NOX) activity were detected in wheat seedling leaves. Under osmotic stress, ABA and Put contents, PM-NOX activity, and PM-NOX-dependent O2.^- production all increased. The inhibitor tungstate (T) of ABA bio-synthesis reduced the increases in ABA and Put contents under osmotic stress. The inhibitor D-arginine (D-Arg) of Put bio-synthesis didn't reduce osmotic-induced increase of ABA, but it inhibited the increases of PM-NOX activity and O2 . ^- production, and the inhibitory effects were reversed by exogenous Put. These findings suggested that ABA might regulate Put biosynthesis, and Put might regulate PM-NOX activity. Treatments with three inhibitors imidazole (I), diphenylene iodonium (DPI) and pyridine (P) of PM-NOX reduced significantly not only O2 . ^- production, but also the stress-induced increase of Put content, which indicated that O2 . ^- production might regulate Put biosynthesis. Treatments with EGTA (Ca²⁺ chelator), La³⁺ and verapamil (V) (Ca²⁺ channel blockers) reduced significantly the stress-induced increase of Put content, which suggested that Ca²⁺ might regulate Put biosynthesis. With these findings, it could be concluded that Put was involved in ABA signaling induced by osmotic stress via regulating PM-NOX activity in wheat seedling leaves.