Sensitivity to ethylene: The key factor in submergence-induced shoot elongation of Rumex

Rosettes of flooding-resistant Rumex palustris plants show a submergence-induced stimulation of elongation, which is confined to the petioles of young leaves, This response increases the probability of survival, It is induced by ethylene that accumulates in submerged tissues. Flooding-intolerant Rumex acetosella plants do not show this response, We investigated whether differences in shoot elongation between the species, between old and young leaves and between the petiole and leaf blade of a R. palustris is plant result from differences in internal ethylene concentration or in sensitivity to the gas, Concentrations of free and conjugated ACC in petioles and leaf blades of R. palustris indicated that ethylene is synthesized throughout the submerged shoot, although production rates varied locally, Nevertheless, no differences in ethylene concentration were found between submerged leaves of various ages, In contrast, dose-response curves showed that only elongation of young petioles of R. palustris was sensitive to ethylene, In R. acetosella, elongation of all leaves was insensitive to ethylene. We conclude that variation in ethylene sensitivity rather than content explains the differences in submergence-induced shoot elongation between the two Rumex species and between leaves of R. palustris.