ABSTRACT
In spite of considerable progress in recent years, the hidden half of plants remains to a large extent an underexplored and underutilized biological frontier. As is clear from the preceding chapters and other recent work (Flores et al., 1998), plant roots show an astounding flexibility in response to the challenges of their complex environment. Throughout the evolutionary history of land plants, roots have evolved sophisticated mechanisms for nutrient acquisition and foraging, interactions with the soil biota, and responses to biotic and abiotic stresses. Underlying most if not all of these adaptations is a remarkable biochemical diversity, which remains largely ignored and poorly understood in spite of its enormous agricultural significance. For example, adaptation to phosphate limitation in the soil involves a major change in the flux of citric acid cycle intermediates, which increased anaplerotic production and secretion of organic acids into the rhizosphere (Lynch, 1998). The increased levels of organic acids in the soil may help release phosphate from bound forms.
