THE EFFECT OF CERTAIN METABOLIC INHIBITORS ON VASCULAR TISSUE DIFFERENTIATION IN ISOLATED PEA ROOTS

Abstract

THE SEQUENCE of events occurring during cellular differentiation may be described and, to some degree, understood in terms of manifest structural changes which the individual cell undergoes during its ontogeny. Yet little is known concerning the biochemical processes in plant tissues which are fundamentally related to these ontogenetic changes. Isolated pea root tips, cultured in the dark in a sterile synthetic nutrient medium, grow in a reproducible manner, showing usual patterns of tissue differentiation. Inhibition of elongation in cultured roots may be produced by a variety of metabolic inhibitors which act through their effect on biochemical processes essential for normal root growth. This paper describes the effects of three inhibitors, indole-3-acetic acid, iodoacetic acid, and 2,4-dinitrophenol on primary vascular tissue differentiation in isolated pea roots which have been subjected in each case to reagent concentrations causing approximately 90 per cent inhibition of root elongation. The purpose of such a study is to attempt to relate biochemical processes to the known anatomical stages in primary vascular tissue differentiation. Attempts to relate root elongation and cellular differentiation have been made in several studies of inhibited root elongation. As early as 1893 Pfeffer reported apparent acceleration of acropetal differentiation of vascular tissue elements in the roots of a number of plants when root elongation was inhibited mechanically by plaster of Paris encasement of the root. Using Vicia faba roots grown in solid gypsum, Pfeffer found acropetal differentiation of pitted vessel elements to within 1 mm. from the tip at the end of 15 days, as compared to 25-35 mm. in uninhibited roots. Pfeffer's finding has been substantiated by numerous subsequent workers (Nathansohn, 1898) . More recently Kojima (1931, 1933), also using the technique of Pfeffer, reported that such mechanical pressure inhibits cell division in the root tip as early as 16 -hr. after beginning treatment. In inhibited roots, xylem elements were apparent at an average distance of 1.4 mm. from the root apex at the end of one week, while in control roots, xylem was apparent first at 13.7 mm. Kojima (1931) pointed out that in terms of position, the inhibited roots appeared to show accelerated differentiation of xylem cells, but in terms of age of cells, cellular differentiation in the inhibited roots was actually hindered. He concluded