Abstract
Roots of cucumber seedlings dominantly exhibit gravitropism, but hydrotropism becomes obvious when grvitropic response is nullified by clinorotation. Auxin transport plays an essential role in root gravitropism, but its role in hydrotropism remains unclear. In this study, we examined the involvement of auxin transport in hydrotropism and gravitropsim in cucumber roots, by using inhibitors of auxin transport and by analyzing expression pattern of CsPIN5 that appeared to be responsible for basipetal transport of auxin from root cap to elongation zone through epidermis and cortex. Inhibitors of auxin efflux substantially suppressed both hydrotropic and gravitropic responses without significant reduction in elongation growth. Furthermore, level of CsPIN5 proteins decreased in the convex side of the hydrotropically and gravitropically responding roots. These results suggest that differential localization of CsPIN5 brings about more auxin transport and accumulation in the concave side of the hydrotropically and grvitropically responding roots, which ultimately leads roots to bending.
