ETHYLENE BIOSYNTHESIS IN REGNELLIDIUM-DIPHYLLUM AND MARSILEA-QUADRIFOLIA

The pathway of ethylene biosynthesis was examined in two lower plants, the semi-aquatic ferns Regnellidium diphyllum Lindm. and Marsilea qua ndrifolia L. As a positive control for the ethylene-biosynthetic pathw ay of higher plants, leaves of Arabidopsis thaliana (L.) Heynh. were i ncluded in each experiment. Ethylene production by Regnellidium and Ma rsilea was not increased by treatment of leaflets with 1-aminocyclopro pane-1-carboxylic acid (ACC), the precursor of ethylene in higher plan ts. Similarly, ethylene production was not inhibited by application of aminoethoxyvinylglycine and alpha-aminoisobutyric acid, inhibitors of the ethylene biosynthetic enzymes ACC synthase and ACC oxidase, respe ctively. However, ACC was present in both ferns, as was ACC synthase. Compared to leaves of Arabidopsis, leaflets of Regnellidium and Marsil ea incorporated little [(14)]ACC and [C-14]methionine into [C-14]ethyl ene. From these data, it appears that the formation of ethylene in bot h ferns occurs mainly, if not only, via an ACC-independent route, even though the capacity to synthesize ACC is present in these lower plant s.