Root system regulation of whole plant growth.

New evidence confirms earlier postulates that root signals to shoots, including abscisic acid, nitrate flux, and cytokinins, modify whole plant growth processes including leaf expansion, stomatal behavior, and biosynthesis of photosynthetic enzymes. Root signals are thought to reflect soil water, nutrient, and mechanical attributes, as sensed by roots. Meristematic activities in root tips initiate changes in root architecture, modifying the soil volume subject to root uptake, and may provide multiple sensory and signaling capabilities. Knowledge of root signals regulating whole plant growth processes suggests new analytical and experimental tools for integrated analysis of plant phasic development, optimal growth, and ecological fitness.