The physiology of micronutrient homeostasis in field crops

Plants have developed a number of transport mechanisms to control the acquisition, partitioning and deposition of the micronutrients iron, copper, zinc and manganese. This control is important because the plants must obtain adequate levels of these essential nutrients for both vegetative acid reproductive tissues, while at the same time preventing excess accumulation. Points of physiological control include various root-system processes, movement and partitioning along the xylem pathway, temporary storage in vegetative compartments, and mobilization via the phloem pathway. The regulation of these control points is not fully understood, although it appears that certain functions may be influenced by interorgan communication. Current evidence does indicate that these processes can be controlled to various degrees; differences exist not only between species, they can also vary temporally and spatially within a given plant. Because this regulatory variability exists, it would appear that enhancing the micronutrient density of edible plant components through the manipulation of physiological processes is an achievable goal. (C) 1999 Elsevier Science B.V. All rights reserved.