ETHYLENE ACCUMULATION IN WATERLOGGED RUMEX PLANTS PROMOTES FORMATION OF ADVENTITIOUS ROOTS

Accumulation of the gaseous plant hormone ethylene is very important f or the induction of several responses of plants to flooding, However, little is known about the role of this gas in the formation of floodin g-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. s hoot elongation and epinasty were also observed, The number of roots i n R. thyrsiflorus Fingerh, was much lower than in R. palustris, which corresponds with the inherent difference in root forming capacity betw een these two species, Ethylene concentrations of 1.5-2 mu l l(-1) ind uced a maximum number of roots in both species. Quantification of ethy lene escaping from root systems of Rumex plants that were de-submerged after a 24 h submergence period showed that average ethylene concentr ations in submerged roots reached 1.8 and 9.1 mu l l(-1) in R, palustr is and R. thyrsiflorus, respectively, Inhibition of ethylene productio n in R. palustris by L-alpha-(2-aminoethoxyvinyl)-glycine (AVG) or alp ha-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 r oots in Rumex species.