Ethylene Action In Plants Research Articles

Inhibitors of Ethylene Biosynthesis and Signaling.

Ethylene is a gas biosynthesized by plants which has many physiological and developmental effects on their growth. Ethylene affects agriculturally and horticulturally important traits such as fruit ripening, post-harvest physiology, senescence, and abscission, and so ethylene action is often inhibited to improve the shelf life of fruits, vegetables, and cut flowers. Chemical inhibitors of ethylene action are also useful for research to characterize the mechanisms of ethylene biosynthesis and signal transduction, and the role that ethylene plays in various physiological processes. Here, we describe the use of three inhibitors commonly used for the study of ethylene action in plants: 2-aminoethoxyvinyl glycine (AVG), silver ions (Ag), and the gaseous compound 1-methylcyclopropene (1-MCP). AVG is an inhibitor of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase, a key enzyme involved in ethylene biosynthesis. Silver and 1-MCP are both inhibitors of the ethylene receptors. Inhibitor use as well as off-target effects are described with a focus on ethylene responses in dark-grown Arabidopsis seedlings. Methods for the use of these inhibitors can be applied to other plant growth assays.

Ethylene action in plants

Ethylene action in plants

THE USE OF 1-MCP AS AN INHIBITOR OF ETHYLENE ACTION IN TULIP BULBS UNDER LABORATORY AND PRACTICAL CONDITIONS

Fusarium infected tulip bulbs produce large amounts of ethylene. During storage and shipping this ethylene causes severe damage in tulip bulbs: an increase in respiration, gummosis, flower abortion (saleable sizes) and excessive splitting (planting stock). The gas 1-methylcyclopropene (1-MCP) is an effective inhibitor of ethylene action in plants by binding to the ethylene receptor. The efficacy of 1-MCP in preventing ethylene effects in tulip bulbs was tested under laboratory and practical conditions. In all experiments, both on a laboratory scale and on a practical scale, the bulbs were fully protected from ethylene by treating them every 12 days for 24 h with 0.2 ppm 1-MCP.

The Effect of the Ethylene Action Inhibitor 1-Cyclopropenylmethyl Butyl Ether on Early Plant Growth

Increased levels of ethylene in plants are responsible for many deleterious effects such as early senescence, fruit deterioration and inhibition of root elongation. Several cyclopropene derivatives have previously been studied as inhibitors of ethylene action in plants. This study focuses on one such compound, 1-cyclopropenylmethyl butyl ether and its effect on the growth of roots and shoots of canola plants as well as rooting of mung bean seedlings. 1-cyclopropenylmethyl butyl ether increased root length in canola plants, but had no significant effect on shoot length. In rooting studies, mung bean seedlings treated with 1-cyclopropenylmethyl butyl ether prior to root excision had fewer numbers of roots than control plants that were not treated with the ethylene action inhibitor. The same rooting study, when repeated in the presence of 1-aminocyclopropane-l-carboxylic acid (ACC), demonstrated an overall increase in the number of roots of inhibitor-treated and non-treated plants, however, the inhibitor was still effective in decreasing the number of roots, compared to its non-treated counterpart.

1-substituted cyclopropenes: Effective blocking agents for ethylene action in plants

A series of 1-alkane substituted cyclopropenes has been prepared and tested as ethylene antagonists using banana fruits as an assay system. 1-Methyl-, 1-ethyl-, 1-propyl-, 1-butyl-, 1-pentyl-, 1-hexyl-, 1-heptyl-, 1-octyl-, 1-nonyl-, and 1-decylcyclopropene were all very active compounds. 1-Methylcyclopropene protected bananas from ethylene with a minimum concentration of 0.7 nl.l−1 after a 24 h exposure. As the carbon chain length was extended the minimum requirement increased some, but starting with 1-butylcyclopropene, the minimum concentration requirement declined and many cyclopropenes were required in lower concentrations than 1-methylcyclopropene. The time of protection at ambient temperature (22–23 °C) was 12 d for 1-methyl-, 1-ethyl-, 1-propyl-, and 1-butylcyclopropene. 1-Pentylcyclopropene protected bananas for 14 d, 1-hexylcyclopropene for 20 d, 1-heptylcyclopropene for 21 d, 1-octylcyclopropene for 25 d, 1-nonylcyclopropene for 35 d, and 1-decylcyclopropene for 36 d.

DOES SILVER INHIBIT ETHYLENE ACTION THROUGH EFFECTS ON APOPLASTIC ENZYMES?

The mechanism by which silver salts interfere with ethylene action in plants is unknown. Prior research indicates that silver acts outside the plasma membrane. We tested a number of plant apoplastic enzymes for inhibition by silver salts. Tomato (Lycopersicon esculentum) fruit pericarp cell wall enzymes, phosphatase, cellulase, peroxidase and polygalacturonase were not inhibited by 100μM AgNO3. At 100μM AgNO3 pectin methyl esterase was inhibited 24.9% and invertase 68.6%; β-galactosidase was inhibited 98.0% by 10μM AgNO3. β-Galactosidase and invertase were not inhibited by silver thiosulfate (STS) at concentrations commonly used to inhibit ethylene action. In other experiments, pea (Pisum sativum) sub-apical hooks were excised and tested in vivo for NADH-ferricyanide oxidoreductase activity. This enzyme was inhibited by 1μM AgNO3 and showed some inhibition by STS. These results indicate that the tomato cell wall enzymes tested are not involved in silver inhibition of plant responses to ethylene. The possible involvement of the oxidoreductase and other plasma membrane enzymes in ethylene action are being considered.

Exploiting the triple response of Arabidopsis to identify ethylene-related mutants.

Alterations in the response of dark-grown seedlings to ethylene (the "triple response") were used to isolate a collection of ethylene-related mutants in Arabidopsis thaliana. Mutants displaying a constitutive response (eto1) were found to produce at least 40 times more ethylene than the wild type. The morphological defects in etiolated eto1-1 seedlings reverted to wild type under conditions in which ethylene biosynthesis or ethylene action were inhibited. Mutants that failed to display the apical hook in the absence of ethylene (his1) exhibited reduced ethylene production. In the presence of exogenous ethylene, hypocotyl and root of etiolated his1-1 seedlings were inhibited in elongation but no apical hook was observed. Mutants that were insensitive to ethylene (ein1 and ein2) produced increased amounts of ethylene, displayed hormone insensitivity in both hypocotyl and root responses, and showed an apical hook. Each of the "triple response" mutants has an effect on the shape of the seedling and on the production of the hormone. These mutants should prove to be useful tools for dissecting the mode of ethylene action in plants.

A Potent Inhibitor of Ethylene Action in Plants

Ag(I), applied foliarly as AgNO(3), effectively blocked the ability of exogenously applied ethylene to elicit the classical "triple" response in intact etiolated peas (Pisum sativumcv. Alaska); stimulate leaf, flower, and fruit abscission in cotton (Gossypium hirsutumcv. Stoneville 213); and induce senescence of orchids (Hybrid white Cattleya, Louise Georgeianna). This property of Ag(I) surpasses that of the well known ethylene antagonist, CO(2), and its persistence, specificity, and lack of phytotoxicity at effective concentrations should prove useful in defining further the role of ethylene in plant growth.

Ethylene Antidote

Abstract One of the most sensitive plant tissues to ethylene is the orchid flower (cover photo). “Dry sepal,” a condition characterized by a progressive drying and fading of the sepals starting at the tip and extending downward, can be triggered by a brief exposure to only several ppb of ethylene. Recently, a potent ethylene antidote was found that will prevent ethylene action in plants including “dry sepal.” It is the most specific and effective plant hormone antidote known. The Cattleya orchids shown on the cover were protected with this ethylene antidote from an ethylene exposure 30 times that which would normally induce this condition.

Concentration Dependencies of Some Effects of Ethylene on Etiolated Pea, Peanut, Bean, and Cotton Seedlings

The effects of a series of concentrations of ethylene (10, 20, 40, to 10,240 nl/l) on elongation, diameter, and geotropism of the stems and roots of etiolated seedlings of Pisum sativum L., Arachis hypogea L., Phaseolus vulgaris L., and Gossypium hirsutum L. were measured or observed. Of the 24 possible responses, 4 were unaffected at the concentrations used, 5 were affected slightly, and the remaining responses exhibited a 14-fold range of apparent half-maximum concentration dependencies (i.e. 95 nl/l for the effect on pea epicotyl geotropism to 1350 nl/l for the promotion of cotton hypocotyl diameter). Six or possibly eight of these responses appear to have the same concentration dependencies while the others fell in pairs or as individual responses. The data, if interpreted in a manner analogous to enzyme kinetics, are indicative of more than one primary mechanism for ethylene action in plants.