Mechanism of Ethylene Action

Abstract

Deuterated ethylene was used to study the mechanism of ethylene action in etiolated pea seedlings (Pisum sativum L. cv. Alaska). No apparent differences were observed in the biological activity of tetradeuteroethylene (CGD4) and ordinary ethylene (C2H4) using the pea stem straight growth assay. The absence of an isotopic effect is discussed in relation to the possibility that ethylene binds to a metal or that carbon to hydrogen bonds of ethylene are broken during its mechanism of action.Analyses by gas chromatography of gas samples obtained from chambers containing intact etiolated pea plants exposed to 2 microliters of C2D4 per liter of air for up to 5 days resulted in no detectable exchange between the deuterium atoms of C2D4 and the hydrogen atoms of the tissue. Similarly, infrared spectra of gas samples obtained from chambers containing strengthen the concept that ethylene binds to a metal. If C2D, were less active, this would also provide some clue as to the chemistry involved in receptor site(s) activation. For example, the formation of an activated complex which involves the cleavage of a carbon-to-hydrogen bond of ethylene would be expected to form more easily with C2H4 than C2D4 because of differences in zero-point energies of the C-H and C-D bonds (16).Molecular changes (e.g., hydrogen exchange, cis-trans-isomerization) may occur in the ethylene molecule itself during receptor site activation because of intermolecular stresses. The detection of such changes, if they occur, would not only aid in the understanding of the biological chemistry involved in ethylene action but would also provide an assay for the isolation of the ethylene-receptor molecule(s) and a technique to explore other questions such as the apparent weak competition between CO, and ethylene for the receptor site (5).MATERIALS AND METHODS Biological Activity of Deuterated Ethylene. Pea seeds (Pisum sativum L. cv. Alaska), soaked in distilled water for 3 hr, were planted in moist vermiculite in plastic trays and were germinated in the dark at 27 C and 70% relative humidity. Sections 7 mm long cut from directly below the plumular hook of 7-day-old etiolated seedlings were placed in Petri dishes with 10 ml of a medium containing 2% sucrose, 0.2 ,uM IAA and 20 mm potassium phosphate buffer, pH 6.8, in double distilled water. Two Petri dishes containing 10 sections each in 200-mm sealed glass desiccators were fumigated with the desired concentration of C2D4 or CM,4. The length of the sections was measured following a 20-hr fumigation period at 27 C in the dark.Isotopic Exchange and cis-trans Isomerization. Approximately 200 pea seeds were germinated in 160-mm glass desiccators as described for the pea straight-growth test. When the seedlings were approximately 3 cm long, the desiccators were sealed and C,D4, cis-C,D,H2, or trans-C2DM2 was added to four such desiccators to give a concentration of 2 to 10 ptl/l. The desiccators were connected in a series with Tygon tubing. Controls were four similar desiccators which contained no seedli...

Ethylene in Plant Growth

“…It has been concluded that ethylene binds to a metal-containing receptor having limited access of approach, with a Km = 6 X 10-10 M (45). The binding must be through a noncovalent bond for no exchange of deuterium occurs when deuterated ethylene is applied to responsive plants (58,59). The transient nature of the binding is also revealed by the fact that many responses to ethylene are rapidly reversible; for example growth inhibition in the etiolated pea stem (Fig.…”

On the stereochemistry of ethylene biosynthesis

“…analysis as before showed glycine (49 mol yo) and a trans: cis ratio of 93 : 7. For (5), 8(D,O, 2H decoupled) 1.19(1 H, d, J 7.7 Hz), and 1.34(1H, d, J 7.7 Hz). We have shown that the presence of glycine does not affect ethylene production from apples.…”