| Abstract: | 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 ( Valt) and its actual operation activity (ρ Valt) decreased more severely. Water stress also led to continuous reduction in cytochrome pathway (CP) activity ( ρ 'Vcyt) and different changes in the contribution of ρ' Valt and ρ' Vcyt to V t in leaves, with ρ Valt/ V t decreasing and ρ 'Vcyt/ V t, increasing. The change pattern of root V t was similar to that of its RWC, while root Valt and ρValt were found to decrease during the first 24 h of stress and thereafter recover to a level close to that of the control (Oh). 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 Valt (also ρValt) 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. |
