Regulatory mechanism unique to root hydrotropism

Abstract

Roots of land plants show gravitropism and hydrotropism in response to gravity and moisture gradients, respectively, for controlling their growth orientation.　It has been shown that in Arabidopsis roots MIZ1 and MIZ2, as well as ABA, play critical roles in hydrotropic response.　Both MIZ1 and ABA responses occur in cortex of the elongation zone.　Auxin negatively regulates hydrotropism in Arabidopsis roots.　On the other hand, auxin transport and redistribution are required for hydrotropic response of cucumber roots.　However, the root cap is dispensable for the induction of hydrotropism in both Arabidopsis and cucumber roots.　These results imply that regulatory mechanisms unique to root hydrotropism exist and that the mechanisms differ among plant species.　This review describes recent development of research on root hydrotropism, with special references to regulatory genes and molecules, signaling systems, and species differences.