Abstract
Plants sense various environmental stimuli and integrate each response to determine growth direction of organs. We have previously shown interference between gravitropism and hydrotropism in seedling roots of several plant species including pea, cucumber and Arabidopsis. To reveal the mechanism of this interference, in this study, we exposed roots of several agravitropic Arabidopsis mutants to the gradient of water potential induced by placing agar plates with different water potentials side by side and analyzed their curvatures. Roots of axr2 mutant that had a gain-of-function mutation in AXR2/IAA7 gene encoding transcriptional repressor of auxin-inducible gene and tir1 afb1 afb2 afb3 quadruple mutant that lacked auxin receptors were defective in hydrotropism, suggesting both tropisms required auxin response. Root curvature of aux1 mutant was greater than that of the wild-type 6 to 24 h after exposure to water potential gradient. Because aux1 mutant was defective in auxin influx carrier, our results suggested that interference between gravitropism and hydrotropism depended, at least in part, on the amount of intracellular concentration of auxin.
