Effect of osmotic stress on the activity of H+-ATPase and the levels of covalently and noncovalently conjugated polyamines in plasma membrane preparation from wheat seedling roots

The influence of osmotic stress on the H+-ATPase (EC 3.6.1.35) activity and the contents of covalently and noncovalently conjugated polyamines were investigated using plasma membrane (PM) vesicles isolated from the roots of wheat (Triticum aestivum L.) seedlings with different drought-tolerance by the sucrose gradient centrifugation method. Results showed that after polyethylene glycol (PEG) 6000 (−0.55 MPa) treatment for 7 days, leaf relative water content (LRWC), relative dry weight increase rate (RDWIR) of seedlings of drought-sensitive Yangmai No. 9 cv. decreased more markedly than that of drought-tolerant Yumai No. 18 cv., while plasma membrane (PM) H+-ATPase activity, the content ratio of noncovalently conjugated polyamine (NCC-PAs) NCC-Spd + NCC-Spm to NCC-Put and the sum contents of covalently conjugated polyamines (CC-PAs) CC-Put + CC-Spd of PM of Yumai No. 18 cv. increased more markedly than that of Yangmai No. 9 cv. Exogenous Spd treatment alleviated osmotic stress injury to Yangmai No.9 seedlings, coupled with marked increases of NCC-Spd and NCC-Spm levels and H+-ATPase activity in the root PM vesicle. Under PEG osmotic stress, the concomitant treatment of drought-tolerant cv. Yumai No. 18 seedlings with methylglyoxyl-bis (guanylhydrazone) (MGBG), an inhibitor of S-adenosylmethionine decarboxylase (SAMDC), and phenanthrolin (o-Phen), an inhibitor of transglutaminase (TGase), caused a decrease of the NCC-Spd + NCC-Spm: NCC-Put ratio and a reduction of sum contents of CC-Put + CC-Spd, respectively. This was associated with decreased PM-H+-ATPase activity and tolerance of seedlings to osmotic stress. Together, these results suggest that tolerance of the wheat seedlings to osmotic stress is associated with the activity of H+-ATPase and the contents of NCC-Spd and NCC-Spm together with CC-Put and CC-Spd in the plasma membrane of roots.