Hydraulic conductivity and contribution of aquaporins to water uptake in roots of four sunflower genotypes

BACKGROUND: This article evaluates the potential of intraspecific variation for whole-root hydraulic properties in sunflower. We investigated genotypic differences related to root water transport in four genotypes selected because of their differing water use efficiency (JAC doi: 10.1111/jac.12079. 2014). We used a pressure-flux approach to characterize hydraulic conductance (L(0)) which reflects the overall water uptake capacity of the roots and hydraulic conductivity (Lp(r)) which represents the root intrinsic water permeability on an area basis. The contribution of aquaporins (AQPs) to water uptake was explored using mercuric chloride (HgCl(2)), a general AQP blocker. RESULTS: There were considerable variations in root morphology between genotypes. Mean values of L(0) and Lp(r) showed significant variation (above 60% in both cases) between recombinant inbred lines in control plants. Pressure-induced sap flow was strongly inhibited by HgCl(2) treatment in all genotypes (more than 50%) and contribution of AQPs to hydraulic conductivity varied between genotypes. Treated root systems displayed markedly different L(0) values between genotypes whereas Lp(r) values were similar. CONCLUSIONS: Our analysis points to marked differences between genotypes in the intrinsic aquaporin-dependent path (Lp(r) in control plants) but not in the intrinsic AQP-independent paths (Lp(r) in HgCl(2) treated plants). Overall, root anatomy was a major determinant of water transport properties of the whole organ and can compensate for a low AQP contribution. Hydraulic properties of root tissues and organs might have to be taken into account for plant breeding since they appear to play a key role in sunflower water balance and water use efficiency. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s40529-014-0075-1) contains supplementary material, which is available to authorized users.