Transpiration response of de-rooted peanut plants to aquaporin inhibitors

Selected genotypes of peanut (Arachis hypogaea L.) have been identified that show constrained transpiration rates (TR) at high atmospheric vapor pressure deficits (VPD) in contrast to genotypes that exhibit continually increasing TR with increasing VPD. The constraint of TR has been proposed as a putative trait for soil water conservation and improved crop performance during late-season water deficits. In soybean (Glycine max (L.) Merr.), limited TR at high VPD has been found to be related to a decreased hydraulic conductance in leaves. A different population of water-transport-mediating proteins, i.e., aquaporins (AQP), was indicated in soybean by measuring the response of shoot TR to treatment with a silver AQP inhibitor. The objective of this study was to test the shoots of four peanut genotypes for a transpiration response when treated with four inhibitors of AQP, which appear to have differing modes of action in inhibiting AQP. Transpiration rate of all four genotypes were equally sensitive to exposure to cycloheximide and mercuric chloride (HgCl ₂). Treatment of the shoots of three genotypes (ICGS 44, TMV 2 and ICGV 86699) with silver nitrate (AgNO ₃) and hydrogen tetrachloroaurate (HAuCl ₄) resulted in decreased TR while treatment of genotype ICGV 91284, which had constrained TR at high VPD, resulted in little or no decrease of TR. In fact, the AgNO ₃ treatment of this fourth genotype resulted in a stimulation of TR at higher AgNO ₃ concentrations. Among the three genotypes with TR not constrained at high VPD, two genotypes had less decrease in TR with HAuCl ₄ treatment than the third genotype. These results identified major differences in shoot response to AQP inhibitors, which were hypothesized to indicate different populations of AQP in the leaves of these peanut genotypes.