Variability of mesophyll conductance and its relationship with water use efficiency in cotton leaves under drought pretreatment.

Drought slows net photosynthetic rate ( A N ) but increases water use efficiency (WUE). Farmers give an artificial drought pretreatment to some crops in the early growth stage and find that yield increases accompanying with the improvement of WUE. We conducted well-watered, non-drought, mild drought and moderate drought pretreatments of potted cotton cultivars. The aims of the present study were to analyse the importance of mesophyll conductance ( g m ) as a factor that may simultaneously improve A N and WUE under drought pretreatment conditions, and to analyse the role of anatomical structure and biochemical mechanism in the variability of g m . Our results showed that significant variability of g m estimated by gas exchange and chlorophyll fluorescence was observed between non-drought pretreatment and drought pretreatment associated with change in A N and WUE. There was great difference in anatomical structure and expression of aquaporins ( GhAQP1 ) among all the treatments. In addition, expression of carbonic anhydrase ( CA ) may not be important in the regulation of g m under drought pretreatment conditions. We concluded that the variability of g m offers a potential target for improving leaf A N and WUE simultaneously by the regulation of anatomical structure and GhAQP1 . [ABSTRACT FROM AUTHOR]