ETHYLENE SENSITIVITY AND RESPONSE SENSOR EXPRESSION IN PETIOLES OF RUMEX SPECIES AT LOW O-2 AND HIGH CO2 CONCENTRATIONS

Rumex palustris, a flooding-tolerant plant, elongates its petioles in response to complete submergence. This response can be partly mimicked by enhanced ethylene levels and low O-2 concentrations. High levels o f CO2 do not markedly affect petiole elongation in R. palustris. Exper iments with ethylene synthesis and action inhibitors demonstrate that treatment with low O-2 concentrations enhances petiole extension by sh ifting sensitivity to ethylene without changing the rate of ethylene p roduction. The expression level of the R. palustris gene coding for th e putative ethylene receptor (RP-ERS1) is up-regulated by 3% O-2 and i ncreases after 20 min of exposure to a low concentration of O-2, thus preceding the first significant increase in elongation observable afte r 40 to 50 min. In the flooding-sensitive species Rumex acetosa, subme rgence results in a different response pattern: petiole growth of the submerged plants is the same as for control plants. Exposure of R. ace tosa to enhanced ethylene levels strongly inhibits petiole growth. Thi s inhibitory effect of ethylene on R. acetosa can be reduced by both l ow levels of O-2 and/or high concentrations of CO2.