ABA-mediated regulation of leaf and root hydraulic conductance in tomato grown at elevated CO ₂ is associated with altered gene expression of aquaporins

Abstract

Elevated CO₂ concentration in the air (e[CO₂]) decreases stomatal density (SD) and stomatal conductance (g_s) where abscisic acid (ABA) may play a role, yet the underlying mechanism remains largely elusive. We investigated the effects of e[CO₂] (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 CO₂ (400 ppm), e[CO₂] stimulated photosynthetic rate in both genotypes, while depressed the g_s only in WT. SD showed a similar response to e[CO₂] as g_s, although the change was not significant. e[CO₂] 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 CO₂ growth environment, e[CO₂] lowered osmotic potential, hence tended to increase turgor pressure particularly for WT. e[CO₂] 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 g_s, SD, and gene expression of aquaporins coordinates the whole-plant hydraulics of tomato grown at different CO₂ environments.

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