Hydraulic Conductance of Maize Hybrids Differing in Transpiration Response to Vapor Pressure Deficit

Limited transpiration rate (TR) under high vapor pressure deficit (VPD) conditions has been proposed as a desirable trait for crop yield improvement. The limited-TR trait has been identified in several single-cross maize hybrids, and among these hybrids, a range in the VPD breakpoint for limited TR was identified. It was hypothesized that the variation in the VPD breakpoint was due to differences in hydraulic conductance in their roots or leaves, or both. Therefore, the objective of this study was to compare relative hydraulic conductance in the roots and leaves across the maize hybrids expressing the VPD breakpoint. It was found that the VPD of the breakpoint was correlated with each of three indices of hydraulic conductance. That is, low VPD breakpoint was associated with low hydraulic conductance in both leaves and roots indicating a common, underlying limiting mechanism in these two tissues. It was hypothesized that expression of similar aquaporin populations influencing hydraulic flow across membranes in the roots and leaves may account for the consistency in results across the indices of hydraulic conductance.