Studies on ethylene binding by cell-free preparations from cotyledons of Phaseolus vulgaris L. : I. Separation and characterisation.

The preparation is described of a cell-free system from developing cotyledons of Phaseolus vulgaris cv. Canadian Wonder which is capable of binding ethylene. The binding is saturable and the apparent dissociation constant for ethylene is 6.4·10(-10) M in solution. The binding site is associated with subcellular particles and treatment with Triton X-100 results in substantial solubilisation of the activity. The kinetics of association and dissociation of the ligand and the binding site are described. The system is heat labile and binding activity is diminished by treatment with some proteolytic enzymes.

Studies on ethylene binding by cell free preparations from cotyledons of Phaseolus vulgaris L. : II. Effects of structural analogues of ethylene and of inhibitors.

Various protein reactive agents such as dithioerythritol, dithiothreitol, mercaptoethanol and p-chloromercuribenzoate inhibit binding of ethylene to cell free preparations of Phaseolus vulgaris L. The effect of the thiols is partially reversed by treatment with diamide; occupation of the binding site by ligand diminishes the inhibition caused by p-chloromercuribenzoate but not that caused by thiols. Growth regulators other than ethylene do not affect binding. Physiologically active structural analogues of ethylene competitively inhibit binding of the growth regulator and their relative effectiveness in the cell free system closely resembles that in developmental processes controlled ethylene.

The compartmentation of ethylene in developing cotyledons of Phaseolus vulgaris L.

Isolated cotyledons of Phaseolus vulgaris L. cv. Canadian Wonder accumulated (14)C2H4 (0.7-1 µl l(-1)) from air to give partition coefficients of 1 to 4, which greatly exceeded the value obtained with steam killed cotyledons (0.05) and with water (0.11). After (14)C2H4 treatment, 98% of the (14)C in the tissue remained as (14)C2H4. The labelled ethylene accumulated by cotyledons was released only slowly (1-10% h(-1)) either in an air stream or into toluene. Heating to 60°C for 2 h, but not freezing and thawing, caused the immediate release of (14)C2H4 from the tissue. Propylene and vinyl chloride competitively inhibited the accumulation of (14)C2H4.Cotyledons emanated endogenous ethylene at a very low rate but after heating (although not freezing and thawing) 13 nl of ethylene per g fresh mass were released within minutes. It was concluded that french bean cotyledons hold ethylene in a compartmented form in sufficient amount to account for at least 200 h of emanation.

Studies on the movement and distribution of ethylene in Vicia faba L.

In Vicia faba ethylene does not appear to move between different parts of the plant in physiologically significant amounts. The 'resistance' to longitudinal movement is such that lateral emanation effectively isolates different parts of the plant from each other. When emanation is prevented, ethylene can be channelled to any part of the plant. Exposure of one section of a plant to (14)C-labelled ethylene (up to 200 µl/l) increased the internal concentration in other parts with ethylene that did not originate from the feeding chamber. A basipetal gradient of endogenous ethylene concentration was found in the lacuna of intact plants, the source of ethylene being the stem tissue. The permeability of stem tissue to ethylene decreases with age. The concentration of ethylene in tissues surrounding the lacuna is always higher than that in the lacuna and it is argued that 'compartmentation' of ethylene occurs within these tissues.

The effect of (2-chloroethyl)phosphonic acid on the sink strength of developing peach (Prunus persica L.) fruit.

The sink strength of one of a pair of competing peach fruits was increased when the fruit was treated with (2-chloroethyl)phosphonic acid (Ethephon) and gibberellic acid. Ethephon increased the capacity of the treated fruit to attract (14)C-labelled assimilates at most stages of fruit development and was most effective when the level of endogenous ethylene produced by the fruit was lowest. The results are discussed in relation to the hypothesis that ethylene participates in the control of sink strength of the fruit and of other competing organs of the tree.

Some characteristics of ethylene production in peach (Prunus persica L.) seeds.

The seed of peach fruits develop the capacity to produce ethylene with a lag phase of about 1 h after excision. The site of ethylene synthesis is in the seed coat and rates as high as 6,000 µl kg(-1) h(-1) were recorded. Ethylene production was reduced to less than 1% of the control by 10 µg/ml cycloheximide. Although the tissue had only a small methionine pool, supplying the seed with exogenous methionine did not influence ethylene production at any stage of seed development. Label from [U-(14)C]methionine was readily incorporated into ethylene.