The Position and Characteristics of ‘Leaky’ Cells in Root Tip Meristems ofHelianthus annuus

Abstract

Sunflower root meristems are composed of two populations of cells which respond differently to stress. One population becomes arrested in G₁ and G₂, while the second ‘leaky’ population (0.25–1.0 per cent) is able to pass through S even during carbohydrate starvation. Leaky cells enter S at a rate of 0.06 per cent cells h⁻¹ after 48 h of starvation. The character of leakiness is retained by roots starved for two successive 48 h starvation periods separated by an 8 h sucrose pulse. Single and double layer autoradiograph experiments demonstrated that leaky cell progeny maintain their leaky character through at least two cell generations. Leaky cells are located at random in the root cap, promeristem, ground meristem, protoderm, cortex, and pericycle. The presence of leaky cells may indicate a stress response mechanism to repopulate the root meristem.