1,3-beta-d-Glucanases from Pisum sativum Seedlings: III. DEVELOPMENT AND DISTRIBUTION OF ENDOGENOUS SUBSTRATES

Two endo-1,3,-beta-d-glucanases (I and II, EC 3.2.1.6) are present in etiolated peas at opposite ends of the stem. Glucanase I from subapical regions degrades substrates to a series of low molecular weight dextrins, and is most readily assayed reductometrically (e.g. as laminarinase). Glucanase II from basal regions preferentially hydrolyzes internal linkages of long chains, and is most sensitively assayed viscometrically (e.g. as carboxymethylpachymanase). The activity of glucanase II but not I increases greatly near the apex in response to treatment of the tissue with auxin, and ethylene gas suppresses endogenous activities and the auxin response, i.e. levels of these enzymes are under developmental controls which can be regulated. Different natural substrates for the two enzymes were identified primarily in tissue fractions soluble in hot water. Substrates for glucanase I are concentrated in apical regions, as is the enzyme itself, and those for glucanase II are in basal regions, implying that enzymes and substrates are normally in separate cellular compartments. Tissue sections stained with aniline blue for beta-glucan show enhanced fluorescence in cell walls, and most of this can be removed either by hot water or the appropriate purified beta-glucanase. The enzymes are not likely to function directly in promoting nutrition or growth in peas, but they could help, following secretion, to maintain channels for communication and translocation through cell walls.