Early activation of plasma membrane H+-ATPase and its relation to drought adaptation in two contrasting oat (Avena sativa L.) genotypes

Major objective of this study is to elucidate the effect of early activation of root hair cell plasma membrane (PM) H+-ATPase on drought adaptation in plants. Pot-culture experiments were carried out to determine oat (Avena sativa L.) genotypic differences in water maintenance, osmotic adjustment and PM H+-ATPase activity at the seedling stage. Two oat genotypes with contrasting drought sensitivity, Dingyou6 (A. vernasativa, drought-tolerant cultivar) and Bende (A. venanuda, drought-sensitive cultivar) were subjected to soil drought stress under environment-controlled growth chamber conditions. At 21 days after emergence, water supply was withheld to allow soils in pots to dry. Our results showed that drought-tolerant “Dingyou6” maintained significantly greater RWC and osmotic potential (OP) in roots and leaves, and also had larger root-to-leaf ratios of RWC and OP than drought-sensitive “Bende” along with 14-day drying process, suggesting that drought-tolerant cv. possesses superior root-to-leaf hydraulic conductivity, and stronger regulatory ability to drought stress. Analysis of the PM H+-ATPase activity and the root and leaf osmolyte contents provided further chemical evidence for this result. Biosynthesis of leaf proline and glycine betaine (GB) followed a similar trend as the activities of root hair cell PM H+-ATPase prior to intermediate stress (around 35% FWC). Significant increase in the activity of PM H+-ATPase was observed at the SWC of about 45–50% FWC, without detectable changes in leaf and root RWC simultaneously. This demonstrated that there existed an early-warning response in roots before the onset of significant decrease in plant RWC. Moreover, the interspecific difference in the timing of triggering early response was obvious. Drought-tolerant “Dingyou6” initiated early response at about 50% FWC, but at about 45% FWC for drought-sensitive cv. This study implies that early activation of root hair cell PM H+-ATPase triggers the increased biosynthesis of major osmolytes, which, in turn, leads to the up-regulation of water maintenance system.