Ethylene accumulation in waterloggedRumexplants promotes formation of adventitious roots

Accumulation of the gaseous plant hormone ethylene is very important for the induction of several responses of plants to flooding. However, little is known about the role of this gas in the formation of flooding-induced adventitious roots. Formation of adventitious roots in Rumex species is an adaptation of these plants to flooded soil conditions. The large air-spaces in these roots enables diffusion of gases between shoot and roots. Application of ethylene to non-flooded Rumex plants resulted in the formation of adventitious roots. In R. palustris Sm. shoot elongation and epinasty were also observed. The number of roots in R. thyrsiflorus Fingerh. was much lower than in R. palustris, which corresponds with the inherent difference in root forming capacity between these two species. Ethylene concentrations of 1.5-2//I I 1 induced a maximum number of roots in both species. Quantification of ethylene escaping from root systems of Rumex plants that were de-submerged after a 24 h submergence period showed that average ethylene concentrations in submerged roots reached 1.8 and 9.1 p\ I"1 in R. palustris and R. thyrsiflorus, respectively. Inhibition of ethylene production in R. palustris by L-a-(2-aminoe thoxyvinyl)-glycine (AVG) or a-aminobutyric acid (AIB) decreased the number of adventitious roots induced by flooding, indicating that high ethylene concentrations may be a prerequisite for the flooding-induced formation of adventitious roots in Rumex species.