A quantitative cytochemical study of determination for xylem-element formation in response to wounding in roots of Pisum sativum L.

Quantitative cytochemical studies of cortical parenchyma cells of roots of Pisum sativum in which the central vascular bundle is severed, showed esterase activity to be an early marker of the determination of cells to form a vascular bridge. Explantation, onto a basal culture medium, of wound segments taken from roots at different times after severing the stele showed the irreversibility of the esterase activity on removal from the inducing environment, so confirming this as a marker of cell determination. A general determination for the stele was shown to occur by 8-10 h after wounding, but information relating to tracheid secondary-cell-wall formation was not apparently available until 18-20 h after wounding. Determination appeared to occur well before mitosis. The timings of the differentiation steps indicate a simple diffusion model to explain the mechanism of arrival of the initiating molecules.