Propylene—A Competitor of Ethylene Action

Abstract

Propylene competed with the ethylene-induced reduction in length growth of the epicotyl of the etiolated garden pea (Pisum sativum L. cv. Alaska). These results constitute further evidence that ethylene acts by attaching itself loosely to a site.pellets. The gases were injected through the plastic bags and the pinholes made by the hypodermic needles were immediately sealed with transparent mending tape. Four days after the gassing the experiment was terminated, and the epicotyl was excised just below the plumular hook and its growth in length was measured RESULTS AND DISCUSSIONThe usage of various types of inhibitors has furnished much information as to the nature of the active site and the type of binding which takes place between the enzyme and the substrate. Competitive inhibition gives direct evidence that enzyme and substrate unite loosely during catalysis without the formation of a covalent bond. To date not much is known about the mode of action of the plant hormone ethylene, nor is there much evidence as to the target of this hormone. As a preliminary step in the search for a possible site of attachment of ethylene, the chemical analogue propylene was tested for its ability to compete with ethylene for a possible site of attachment. Propylene was chosen as a possible inhibitor of ethylene action because earlier we (5) had noticed that treatment of etiolated pea seedlings with ethyl propylphosphonate, which had been found to release ethylene and propylene in a proposed model system (8), did not show a very clear cut triple response. (The term "triple response" was coined by Knight and Crocker [6]. In their paper they justifiably credit Neljubow with the discovery of the "triple response." These workers defined triple response in pea seedlings as follows:[a] change of negative geotropism to diageotropism; [b] increased growth in thickness; [c] reduced rate of growth in length.) It was theorized (4) that the simultaneous evolution of propylene from this chemical might have been antagonistic to the hormone. MATERIALS AND METHODSSeeds of Pisum sativum L. cv. Alaska were purchased locally, leached overnight in running tap water, planted 50 per pot at equal depth in vermiculite, and kept in the dark in a growth chamber. All manipulations such as watering and the injecting of gas was done using a green safelight. When the seedlings had reached a height of 2 to 3 cm, they were watered and the pots were placed into airtight growth chambers consisting of a plywood frame 31.5 x 52 x 30 cm, sealed within a polyethylene bag. Each growth chamber contained a dish filled with potassium hydroxide

Is the Diageotropic Tomato Ethylene Deficient?

“…Indeed in etiolated pea seedlings the opposite effect has been found. High and non-physiological concentrations of ethylene induced slow horizontal growth and the application of inhibitors of ethylene action preserved the plants' vertical position (Simons andDiBey 1971, DoUwet andSeeman 1975).…”