Strategy I and strategy II mechanisms affecting iron availability to plants may be established too narrow or limited

Abstract

In order to denote differences in mechanisms for iron uptake, two very different strategies have been suggested for the acquisition of iron in the plant kingdom. In Strategy I (in most non‐graminaceous species), it has been suggested that reduction of Fe(III) is an obligatory step in making iron available to the plant. Whereas in Strategy II (in grasses) the reduction of Fe(III) is not involved in uptake of Fe phytosiderophores. For Strategy I plants, emphasis has been placed on an inducible plasma‐membrane‐bound reductase with hydrogen ion release from roots; very little emphasis is given to release of reductants by roots or a role for citrate in transporting Fe as Fe‐citrate to plant tops. Factors initiated in response to Fe‐deficiency stress for K‐deficient tomatoes and soybeans and plants grown under two different light sources will be discussed indicating release of reductants by roots may be an important factor essential to uptake of iron in Strategy I plants. Both Fe‐inefficient and Fe‐efficient corn and oats have been studied for their response to Fe‐deficiency stress, except for a possible role for a phytosiderophore, and the latter needs to be examined. Barley, wheat, oats and corn (Strategy II plants) take up much less calcium, differ in their response to phosphate, excess BPDS (Fe(II) chelator), and calcareous soils, and are more susceptible to Cu‐deficiency than soybeans (Strategy I plant). These factors need to be recognized as we try to establish a role for a phytosiderophore in these plants. The Fe‐inefficient corn or oats could produce less or no phytosiderophore compared to the Fe‐efficient plants. It may be too early to establish such narrow limits to the factors that may be involved in making Fe available to Strategy I and to Strategy II plants.