Effects of major vein blockage and aquaporin inhibition on leaf hydraulics and stomatal conductance

The density and architecture of leaf veins determine the network and efficiency of water transport within laminae and resultant leaf gas exchange and vary widely among plant species. Leaf hydraulic conductance (K(leaf)) can be regulated by vein architecture in conjunction with the water channel protein aquaporin. However, our understanding of how leaf veins and aquaporins affect leaf hydraulics and stomatal conductance (g(s)) remains poor. By inducing blockage of the major veins and inhibition of aquaporin activity using HgCl(2), we examined the effects of major veins and aquaporins on K(leaf) and g(s) in species with different venation types. A vine species, with thick first-order veins and low vein density, displayed a rapidly declined g(s) with high leaf water potential in response to vein blockage and a greatly reduced K(leaf) and g(s) in response to aquaporin inhibition, suggesting that leaf aquaporins are involved in isohydric/anisohydric stomatal behaviour. Across species, the decline in K(leaf) and g(s) due to aquaporin inhibition increased linearly with decreasing major vein density, possibly indicating that a trade-off function between vein architecture (apoplastic pathway) and aquaporin activity (cell-to-cell pathway) affects leaf hydraulics.