AN ETHYLENE-MEDIATED INCREASE IN SENSITIVITY TO AUXIN INDUCES ADVENTITIOUS ROOT-FORMATION IN FLOODED RUMEX PALUSTRIS SM

The hormonal regulation of adventitious root formation induced by floo ding of the root system was investigated in the wetland species Rumex palustris Sm. Adventitious root development at the base of the shoot i s an important adaptation to flooded conditions and takes place soon a fter the onset of flooding. Decreases in either endogenous auxin or et hylene concentrations induced by application of inhibitors of either a uxin transport or ethylene biosynthesis reduced the number of adventit ious roots formed by flooded plants, suggesting an involvement of thes e hormones in the rooting process. The rooting response during floodin g was preceded by increased endogenous ethylene concentrations in the root system. The endogenous auxin concentration did not change during flooding-induced rooting, but a continuous basipetal transport of auxi n from the shoot to the rooting zone appeared to be essential in maint aining stable auxin concentrations. These results suggest that the hig her ethylene concentration in soil-flooded plants increases the sensit ivity of the root-forming tissues to endogenous indoleacetic acid, thu s initiating the formation of adventitious roots.