The mechanism of the action of the growth substance of plants

Publisher Website
Google Scholar
Abstract
These studies were designed to show the relation between the growth substance which enters the Avena coleoptile and the new cell-wall which is laid down as a result of it. By placing agar blocks containing the purified growth substance on the stumps of coleoptiles, and measuring the increase in growth (elongation) which resulted, the relation between conc. of growth substance applied and total elongation was found to be linear over a considerable range. The actual amount of the growth substance which passed out of the agar block into the plant under the conditions used was also detd., by removing the agar blocks and assaying the growth substance left in them by the curvature technique of Went. The weight of cell wall in the coleoptile was 0.0164 mgm. per mm. length, and, of this, analysis showed 8% was pectin, 28% hemicellulose, 12% protein and 42% cellulose. Hence it was calculated that, in the linear range of the reaction, 1 molecule of growth substance acts in the laying down of 3 X 105 hexose residues as cellulose, or about 150 cellulose micelles. There is therefore no stoichiometrical relationship between the growth substance and the skeletal material of the cell wall. An independent method, involving measurement of the area and thickness of the cell-walls, and hence calculation through the volume, gave essentially the same result. Furthermore, from the fact that the growth substance is an organic acid, the area of the molecule was calculated and from this it follows that in growth not enough molecules of it are present to form a monomolecular layer over the new cell-wall area. The growth substance therefore cannot act through causing change of permeability. It follows that it acts, not directly upon the cell wall, but in some indirect way whereby each molecule exerts its influence a number of times, i.e., as a catalyst or true hormone.

This publication has 3 references indexed in Scilit: