Light- and dark-grown Potamogeton pectinatus, an aquatic macrophyte, make no ethylene (ethene) but retain responsiveness to the gas

Abstract

Plants of Potamogeton pectinatus L., growing rapidly from small tubers in the dark or from 12-week-old light-grown plants, contained high concentrations of the ethylene precursor 1-amino-cyclopropane- 1-carboxylic acid (ACC) (4.8 – 25.6 nmol g^-1 fresh weight). However, ethylene (ethene) production was either completely absent or too small to raise concentrations significantly above background when measured by flame ionization gas chromatography sensitive to <0.04 µmol m^-3. Seedlings of pea (Pisum sativum L.) of similar size produced ethylene in readily detectable amounts although concentrations of endogenous ACC concentrations were much smaller than in P. pectinatus. Large amounts of exogenous ACC (10 mM) supplied for 4 h or 15 h failed to induce ethylene production in dark-grown P. pectinatus but raised it marginally above background levels in light-grown shoots. In contrast, a substantial effect was seen in pea shoots. When 25 mM ACC was supplied, a small amount of ethylene was released by dark-grown P. pectinatus but the rate was less than 0.5% of that measured from pea plants treated similarly. An absence of ACC oxidase enzyme activity in extracts of P. pectinatus showed that the last step in the ethylene biosynthetic pathway is constitutively arrested in mature plants grown in the light and in young plants regenerating from tubers in the dark. Despite an inherent inability to synthesise ethylene, P. pectinatus remained responsive to applied ethylene. Leaf extension and adventitious rooting from stem nodes were promoted strongly by 0.41 mmol m^-3 ethylene, whereas applications of ACC had no effect on growth or development.