From a variety of undifferentiated plant cell suspensions, 2,4-dichlorophenoxyacetic acid-dependent cells of sunflower (Helianthus annuus L. Spanners Allzweck) produced large quantities of ethylene. The maximum rate was about 1 nanomole x gram fresh weight-' x hour-' during the exponential growth phase. The action of various compounds known to interfere with ethylene formation in plant tissue was studied in sunflower cell suspensions. The influence on ethylene, 1-aminocyclopropanecarboxylic acid (ACC), and N-malonyl-ACC (MACC) Undifferentiated plant cell suspensions are able to produce ethylene depending on the kind of plant from which the cell originated but also on their physiological state (2-4, 15, 17, 21, 24). With respect to its physiological significance, data suggested no functional relationship between growth and ethylene synthesis (10,15,24). Ethylene was assumed to be a by-product of actively dividing cells. Nevertheless, undifferentiated cell suspensions should be an appropriate tool for analyzing in detail the effects of biologically active compounds on cellular ethylene biosynthesis.In particular, plant growth retardants of the norbornenodiazetine (e.g. tetcyclacis) and triazole (e.g. LAB 150 978) type inhibited both the formation of ethylene and shoot growth of sunflower seedlings (25). Likewise, preliminary results indicated that both compounds decreased the ethylene production and cell division rate in cell suspensions of sunflower (24). Although their mode of action in regulating growth processes is seen in an interaction with gibberellin and to some extent sterol biosynthesis (5,7,12,22), the question arises as to whether there is a direct effect on ethylene biosynthesis, too.In the work reported we have analyzed the levels of ethylene and ACC2 produced in undifferentiated sunflower suspension cells under the influence of the growth retardants tetcyclacis and LAB 150 978. In addition to ACC, the direct precursor of eth-' Dedicated to Professor Dr. Helmut Doerfel on the occasion of his 60th birthday. The cells, grown in culture for several years, were subcultured at intervals of 7 d in the exponential growth phase under the following conditions: 250 ml Erlenmeyer flasks containing 80 ml of cell suspension were shaken on a rotary shaker at 110 rpm in the dark at 25°C. Solutions of chemical compounds used were prepared in acetone or in water (sterile-filtered) and were added to the medium shortly before inoculation. The final acetone concentration in the medium (1%) had no adverse effects on the growth of the culture.
Abstract. During the incubation of undifferentiated cell suspensions of sunflower (Helianthus annuus L. cv. Spanners Allzweck) ethylene production was effectively inhibited by the novel oxime ether derivative LAB 181 508, [[(Isopropyliden)-amino]-oxy]-acetic acid-2-(methoxy)-2-oxoethylester (PACME). The compound was most active during the first 6 days of incubation exhibiting a value of 50% inhibition at 9.5 • 10 -6 mol x L -~. The pattern of changes in the internal l-aminocyclopropanecarboxylic acid (ACC) and N-malonyl-ACC (MACC) levels paralleled the influence on ethylene formation. While the addition of ACC fully restored ethylene production, applied S-adenosyl-Lmethionine (SAM) was not effective. Experiments with [~4C]indole-3-acetic acid (IAA) revealed that LAB 181 508 did not affect auxin uptake into suspension cells of sunflower. The results suggest that LAB 181 508 reduces ethylene formation by inhibiting the conversion of SAM to ACC in the biosynthetic pathway. In comparison to the structurally related inhibitor of ACC synthase, aminoethoxyvinylglycine (AVG), LAB 181 508 reduced growth and viability of the suspension cells only slightly. Low phytotoxicity of LAB 181 508 combined with a less complicated chemical synthesis might offer interesting aspects for physiological research and horticultural and agricultural practice.Ethylene influences many processes in the development and yield formation of plants (e.g., fruit set and ripening, senescence, and stress reactions)
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