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

Abstract

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.