title: Production and Release of Ethylene from 1-aminocyclopropane-1-carboxylic Acid in Lemna minor L. in the Dark and at Different Carbon Dioxide Compensation Concentrations.
abstract: Duckweed Lemna minor L. was used to investigate the in vivo conversion of 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene in the dark and at different CO(2) compensation concentrations. The plants were incubated in closed bottles. Various constant CO(2) concentrations in the range 50 to 1000 ppm were obtained by applying different light intensities. During the incubation on ACC-containing solution (0.01 -1000 μM) in the dark, ACC accumulated in L. minor, and no saturation of ACC uptake occurred. ACC-dependent ethylene production, on the other hand, was saturated above 10 μM ACC (equivalent to 32 μM internal ACC). V(max) was 3.18 nmol h(-1) (g fresh wt)(-1) and apparent K(m) was 8.71 μM internal ACC. In the light, CO(2) below 1000 ppm was limiting for ACC-dependent ethylene production. In the presence of 1 and 10 μM ACC, half-maximum CO(2) activity was at 114 and 163 ppm, respectively. CO(2)-stimulation was very small at 0.1 μM external ACC and virtually absent in the case of basal ethylene production. Under non-limiting CO(2), ACC-dependent ethylene production rates in the light were higher than V(max) in darkness. The mechanism of COrstimulation of ACC-dependent ethylene production in the light was elucidated by comparing rates of ACC conjugation, and ethylene synthesis, release and retention under high and low CO(2). Inhibition of ethylene retention contributed the largest portion to the enhancement of ethylene emanation from L. minor under high CO(2) observed. However, a small stimulatory effect of CO(2) on ACC conversion to ethylene was also found, while the conjugation of ACC was not significantly affected by CO(2).
authors.affiliation: Institute of Plant Physiology, University of Bern, Altenbergrain 21, CH-3013 Bern, Switzerland.
authors.forename: J
authors.initials: J
authors.lastname: Fuhrer