COPPER-INDUCED ETHYLENE BIOSYNTHESIS IN TERRESTRIAL (NICOTIANA-TABACUM) AND AQUATIC (SPIRODELA-OLIGORRHIZA) HIGHER-PLANTS

Induction of ethylene biosynthesis by cupric ions was compared using leaf discs from a terrestrial plant (tobacco; Nicotiana tabacum L. cv Xanthi) and whole fronds of an aquatic plant (Spirodela oligorrhiza). In both systems, induction of ethylene biosynthesis was greatest in younger leaves, was not inhibited by the protein synthesis inhibitor cycloheximide, was inhibited by the lipid peroxidation/singlet oxygen inhibitor DABCO, and was stabilized by D2O in the light. However, selenomethionine stimulated copper-induced ethylene production in tobacco leaf discs but was inhibitory in Spirodela. Incorporation of radioactive methionine into ethylene in copper-treated tobacco leaf discs but not Spirodela plants was markedly reduced by the addition of 2.5 mM ACC. In the presence of cupric ions, Spirodela converted methionine as well as linoleic acid to ethylene to similar extents, whereas tobacco leaf discs were more efficient in converting methionine than linoleic acid to ethylene. Together, these results suggest that both these plants produce ethylene in response to cupric ions albeit via different biosynthetic routes.