SummaryRumex palustris responds to total submergence by increasing the elongation rate of young petioles. This favours survival by shortening the duration of submergence. Underwater elongation is stimulated by ethylene entrapped within the plant by surrounding water. However, abnormally fast extension rates were found to be maintained even when leaf tips emerged above the floodwater. This fast post-submergence growth was linked to a promotion of ethylene production that is presumed to compensate for losses brought about by ventilation. Three sources of ACC contributed to post-submergence ethylene production in R. palustris: (i) ACC that had accumulated in the roots during submergence and was transported in xylem sap to the shoot when stomata re-opened and transpiration resumed, (ii) ACC that had accumulated in the shoot during the preceding period of submergence and (iii) ACC produced de novo in the shoot following de-submergence. This new production of ethylene was associated with increased expression of an ACC synthase gene (RP-ACS1) and an ACC oxidase gene (RP-ACO1), increased ACC synthase activity and a doubling of ACC oxidase activity, measured in vitro. Out of seven species of Rumex examined, a de-submergence upsurge in ethylene production was seen only in shoots of those that had the ability to elongate fast when submerged.

Extraction of isoflavone malonylglucosides from red clover (Trifolium pratense L.) is a complicated procedure. This is due to the relatively unstable character of the thermolabile glucoside malonates as well as by action of native beta-glucosidases, resulting in a rapid degradation of malonylated glucosides into their corresponding aglucones. In this study, Tris was identified as a suitable beta-glucosidase inhibitor in red clover extracts, optimized at 350 mM Tris in 80% ethanol at pH 7.2. Extraction of fresh red clover leaves using Tris increased the concentration of malonate conjugated isoflavones approximately 13 to 24 times as opposed to extraction without Tris. A comparison of isoflavone profiles obtained after extraction with and without Tris of different plant organs of red clover and several species within the family Fabaceae suggests that the amount and/or activity of the degenerative beta-glucosidase enzymes vary for the different plant parts of red clover and among the species studied. Therefore, the use of standard extraction methods may well result in overestimation of the concentration of aglucones and consequently underestimation of the malonylglucoside isoflavones concentration depending on the plant species and plant part studied.