Effects of water stress on the cyanide-resistant respiration and expression of the alternative oxidase gene in wheat seedlings

The effects of water stress on the development and operation of an alternative respiratory pathway and the expression of an alternative oxidase gene in wheat ( Triticum aestivum L. cv. Longchun No. 16) seedlings were investigated. When the roots of the seedlings were osmotically stressed with 0.5 MPa polyethylene glycol (PEG 6000) solutions for 24, 48 and 72 h, the leaves were subjected to mild, moderate and severe water stress respectively, while the roots only received mild water stress throughout the stress treatment as reflected by changes in relative water content (RWC). In response to the water-stress conditions, the alternative pathway capacity (V-alt), the alternative pathway activity (rho V-alt) and its contribution to total respiration (rho V-alt/V-t) of leaves decreased progressively, while these parameters of roots were found to decrease at the first 24 h of stress and thereafter recover to the levels close to that of the control (0 h). These data indicate that the alternative pathway is sensitive to water stress and is adaptive to mild water stress. The results of Northern hybridization performed with total cellular RNA and an alternative oxidase gene (Aox) probe revealed that there was a good correlation between V-alt(also rho V-alt) and the level of Aox mRNA in both leaves and roots, suggesting that the water stress-induced decrease in the development and operation of alternative pathway was due, at least in part, to the inhibition of expressional synthesis of the alternative oxidase protein.