Identification of the Functional Tissues for Hydrotropism in Comparison with Those for Gravitropism

Abstract

Hydrotropism is a response of roots to a moisture gradient. Our previous studies suggest that hydrotropism is interfered with gravitropism, however, this interacting mechanism is hardly uncovered. To approach this problem, we intended to compare the functional tissues responsible for both tropisms. We irradiated either laser beam or heavy-ion beam to root tissues and monitored the changes in tropic responses. Laser beam irradiation to either elongation zone or columella cells resulted in marked decrease in both tropic curvatures. Similar effect was observed when heavy-ion beam was irradiation to elongation zones. Irradiation of either beams to elongation zone resulted in a decrease in root growth. However, the heavy-ion beam irradiation to columella cells affected neither root tropism nor growth. Considering the non-destructive cell inactivation effect of heavy-ion beam, our results suggest that the interacting process between both tropisms, which occurs inside columella cells, do not require de novo gene expression.