Molecular Requirements for the Biological Activity of Ethylene

Abstract

Summary. The molecular requirements for ethylene action were investigated using the pea straight growth test. Biological activity requires an unsaturated bond adjacent to a terminal carbon atom, is inversely related to molecular size, and is decreased by substitutions which lower the electron densitv in the unsaturated position. Evidence is presented that ethylene binds to a metal containing receptor site. 002 is a competitive inhibitor of ethylene action, and prevents high concentrations of auxin (which stimulate ethylene formation) from retarding the elongation of etiolated pea stem sections. It is suggested that CO2 delays fruit ripening by displacing the ripening hormone, ethylene, from its receptor site. Binding of ethylene to the receptor site is also impeded when the 02 concentration is lowered, and this may explain why fruit ripening is delayed at low O. tensions.Several gases in addition to ethylene elicit the triple response in etiolated seedlings, and the concentration of each requlired to produce a just discernible effect has been determined (9, 25). Included are propylene, butylene (isomer unknown), acetylene, and CO. Since these vapors also substitute for ethylene in causing epinasty (9, 10), fruit ripening (11,27), and other effects (8,9, 29), it would appear that the molecular requirements for biological action are similar in each case. We have attempted to delineate these requirements using as an assay for ethylene action the effect which the gas has on the growth and tropistic behavior of etiolated pea stem sections. Materials and MethodsPeas (Pisum sativum, var. Alaska) were soaked in water for 5 hours and germinated in moist vermiculite. The seedlings developed in darkness at 230 receiving an occasional exposure to dim red illumination, and were used on the seventh day. Sections 10 mm long were cut from the third internode just below the leaf hook and incubated in a medium containing 1 uM indole-3-acetic acid (IAA), 2 % sucrose (w/v), 0.05 M potassium phosphate buffer (pH 6.8), and 5 ptM CoCl in glass distilled water. Ten ml of media and 10 sections were placed in a 125 ml Erlenmeyer flask, this was sealed with a vaccine cap, the gas phase ad-'This investigation was supported by research grants EF-00214 and EF40078&2 from the United States Public Health Service, Division of Environmental Engineering and Food Protection, and was carried out while S. P. Bukrg was the recipient of Career Research DevelopmentAward 1-K3-GM-6871 from the USPHS. justed as described below, and the tissue slowly shaken at 230 in the dark. After 3 hours the sections were visually scored in red light for curvature and 15 hours later the gas phase was analyzed by gas chromatography before the tissue was removed, blotted dry, weighed and measured. Details of the procedure have been published elsewhere (4). Gas Chromatography and Preparation of GasM&ixtures. All gases were chromatographed on a 3 foot alumina column to determine whether ethylene or other low molecular weight contaminants were present. The instrument, a Perk...

Respiration rate and ethylene metabolism of ‘Jonagold’ apple and ‘Conference’ pear under regular air and controlled atmosphere

“…Indeed CO 2 stimulates ACC-oxidase activity in vitro with an optimal in the range of 2 kPa (John 1997). However, at higher partial pressures, CO 2 acts as a competitive inhibitor of ethylene action (Burg and Burg 1967). In accordance with these observations, there are other results such as the use of CO 2 partial pressures up to 5 kPa to inhibit ACC-oxidase and ACC-synthase (Bufler 1986) as well as the induction of mRNA (Gorny and Kader 1996).…”

Role of internal atmosphere on fruit ripening and storability—a review

“…The inhibitory effect of CO 2 on auto-induced ethylene production in climacteric fruits could be due to competition between CO 2 and ethylene for the same active site (Burg and Burg 1967;Mathooko et al 1995). As per Burg and Burg (1967), the amount of CO 2 in the intercellular spaces of fruits at pre-climacteric stage is low but this may approach to higher levels of around 10% during ripening and post-climacteric phase. This higher endogenous level of CO 2 probably raises the threshold concentration of ethylene to higher levels for its action in fruits.…”

“…2). It has already been reported that O 2 is required for the synthesis as well as the action of ethylene in fruits including tomato (Burg and Burg 1967). Fruits show reduction in respiration with lowering of O 2 in the surrounding atmosphere and at specific reduced level of O 2 there is induction of anaerobic respiration which leads to fast breakdown of sugars and this is named as the Pasteur effect (Kader 1986;Boersig et al 1988).…”

Two Leucine-Rich Repeat Receptor Kinases Mediate Signaling, Linking Cell Wall Biosynthesis and ACC Synthase in Arabidopsis

“…This model is possible, but two lines of evidence argue somewhat against it. First, it would not explain the lack of root swelling in various ethylene biosynthesis mutants; second, it is probable that, similar to ETR1 and its paralogs, any additional ethylene receptor would be blocked by silver ion (Burg and Burg, 1967), and thus silver should, but does not, revert the fei1 fei2 phenotype. A final model that is consistent with the data is that ACC itself, rather than ethylene, acts as a signaling molecule to regulate cell expansion in the FEI/SOS5 pathway.…”