Abstract
Water and salt stresses reduce net CO(2) assimilation (A(N)) primarily by restricting stomatal conductance (g(s)) and mesophyll conductance (g(m)), while altering leaf structure, anatomy, and cell wall composition. Although some reports observed relationships between these modifications and g(m), in others they remain less clear. Here, we compiled data on studies in which major cell wall components (cellulose; C, hemicellulose; H; pectins; P) were determined with photosynthetic, structural and anatomical features, obtaining a dataset presenting distinct species subjected to both stresses. Among parameters previously reported to affect g(m) (leaf mass per area: LMA; chloroplast surface area exposed to intercellular air spaces per unit of leaf surface area: S(c)/S; fraction of intercellular air spaces: f(ias); cell wall thickness: T(cw)), pectins and the P/(C + H) ratio were the unique consistently varying in salt- and water-stressed plants. Despite no single trait correlated with g(m), it was positively linked with [P/(C + H) × S(c)/S × f(ias)]/[T(cw) × Lignin × LMA] in studies in which all parameters were tested, suggesting that distinct traits may exert antagonistic influences on g(m). Although further experiments are needed to reinforce our findings, we hypothesize that increases in pectins under stress could limit larger g(m) declines, improving g(m)/g(s) ratio and water use efficiency (WUE).