Properties and Possible Physiological Significance of Cell Wall Calcium Binding in Etiolated Pea Epicotyls

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Abstract
Baydoun, E. A-H. and Brett, C. T. 1988. Properties and possible physiological significance of cell wall calcium binding in etiolated pea epicotyls.—J. exp. Bot. 39: 199–208. The binding of 45Ca2+ ions to cell walls prepared from pea epicotyls was examined in young and old parts of the epicotyl, and was found to be considerably greater, on a carbohydrate basis, in the older, non-growing cells. A similar comparison between light- and dark-grown stems showed greater binding in the dark-grown stems. The polygalacturonase-insensitive component of the binding contained at least three types of binding with different affinities, and had an apparent pK of 4.3. The specificity of the binding for calcium ions was examined and a considerable degree of specificity was observed. The specificity of inhibition by calcium of epicotyl elongation was similar to the specificity of calcium binding. A specific calcium chelator, EGTA, when present at a concentration of above 10 mol m−3, promoted the extension of mature regions of the epicotyl, while inhibiting extension of younger tissue.

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