Cortical Cell Breakdown and Lateral Root Primordium Development inVicia fabaL

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Abstract
The effect of the formation of a cavity in the cortex of the primary root of Vicia faba adjacent to lateral root primordia on root development has been investigated. Premature exposure of such primordia to the external medium by removing the overlying tissues of the primary root has no effect on primordium development if that primordium was within 48 h of emerging as a lateral root. Similar exposure of primordia which were at an earlier stage of development and consisted of between 3400 and 7000 cells resulted in the generation of a stationary phase, with most of the nuclei arrested in G1 (presynthetic interphase), 48–72 h after exposure began, followed by nuclear degeneration by 96 h. Since no mature vascular tissue was found in these primordia until after they emerged as secondary roots, all of the nutrients necessary for the maintenance of cell proliferation in these meristems must reach them by simple diffusion from the surrounding medium. A preliminary analysis of the liquid contents of the cavity next to developing primordia demonstrates it to be rich in carbohydrates and it is clear, from the results reported in this paper, that cell proliferation in primordia, consisting of a mean number of 5400 cells, is largely dependent on the substances present in the cavity fluid, although some materials reach the primordium by diffusion from the cells of the primary root to which the primordium remains attached.

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