Osmotic
dehydration of wheat seedlings in -0.5 MPa
polyethylene glycol (PEG) solutions for 24, 48 and 72 h resulted in mild, moderate and severe
water stress respectively in leaves, but only caused mild
water stress in roots as reflected by the changes in relative water content (RWC). In response to the above
water stress conditions, leaf total respiratory rate (V(t)) decreased progressively, and the alternative pathway (AP) capacity (V(alt)) and its actual operation activity (rhoV(alt)) decreased more severely.
Water stress also led to continuous reduction in
cytochrome pathway (CP) activity ((rho' V (cyt)) and different changes in the contribution of rhoV(alt) and rho'V(cyt) to V(t), in leaves, with rhoV(alt)/ V(t), decreasing and rho'V(cyt)/V(t) increasing. The change pattern of root V(t) was similar to that of its RWC, while root V(alt) and rhoV(alt) were found to decrease during the first 24 h of stress and thereafter recover to a level close to that of the control (0 h). These data indicate that the alternative pathway is sensitive to
water stress and can adapt mild
water stress. The results of northern hybridization using an
alternative oxidase gene (Aox) as probe revealed that there was a good correlation between V(alt) (also rhoV(alt)) and Aox
mRNA levels in both leaves and roots, suggesting that
water stress affects the development and operation of AP respiration through affecting the expression of the
alternative oxidase gene.