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 pl ant growth processes including leaf expansion, stomatal behavior, and biosynthesis of photosynthetic enzymes. Root signals are thought to re flect soil water, nutrient, and mechanical attributes, as sensed by ro ots. Meristematic activities in root tips initiate changes in root arc hitecture, modifying the soil volume subject to root uptake, and may p rovide multiple sensory and signaling capabilities. Knowledge of root signals regulating whole plant growth processes suggests new analytica l and experimental tools for integrated analysis of plant phasic devel opment, optimal growth, and ecological fitness.