ABA-mediated regulation of leaf and root hydraulic conductance in tomato grown at elevated CO2 is associated with altered gene expression of aquaporins

Elevated CO_(2)concentration in the air(e[CO_(2)])decreases stomatal density(SD)and stomatal conductance(gs)where abscisic acid(ABA)may play a role,yet the underlying mechanism remains largely elusive.We investigated the effects of e[CO_(2)](800 ppm)on leaf gas exchange and water relations of two tomato(Solanum lycopersicum)genotypes,Ailsa Craig(WT)and its ABA-deficient mutant(flacca).Compared to plants grown at ambient CO_(2)(400 ppm),e[CO_(2)]stimulated photosynthetic rate in both genotypes,while depressed the gs only in WT.SD showed a similar response to e[CO_(2)]as gs,although the change was not significant.e[CO_(2)]increased leaf and xylem ABA concentrations and xylem sap pH,where the increases were larger in WT than in flacca.Although leaf water potential was unaffected by CO_(2)growth environment,e[CO_(2)]lowered osmotic potential,hence tended to increase turgor pressure particularly for WT.e[CO_(2)]reduced hydraulic conductance of leaf and root in WT but not in flacca,which was associated with downregulation of gene expression of aquaporins.It is concluded that ABA-mediated regulation of gs,SD,and gene expression of aquaporins coordinates the whole-plant hydraulics of tomato grown at different CO_(2)environments.