An evaluation of concepts related to iron-deficiency chlorosis

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Abstract
The essential role of Fe in the biological world is impressive and the manner in which the Fe supply is controlled to the plant or organism is unique in making Fe available for use. Each investigator has pursued specific approaches to answer detailed objectives in a designated line of research; these have primarily dealt with the Fe‐stress response mechanism of dicotyledonous plants. These plants respond to Fe‐deficiency stress by (a) release of hydrogen ions and (b) release of reducing compounds from their roots, (c) reduction of Fe3+ to Fe2+ by their roots, and (d) increases in organic acids (particularly citrate) in their roots. Each of these factors will be discussed in view of existing hypotheses emphasizing reduction by roots at the plasma membrane and with regard to how these factors may compliment each other in the absorption process. Mugeneic acid has been isolated from roots of iron‐deficiency stressed barley and oats and dlbutyl phthalate from sorghum. In each case iron was made available for use by the plant. Hydroxamate siderophores of mlcrobial origin have supplied iron to Fe‐efficient tomato (T3238FER), but not to the Fe‐inefflcient tomato (T3238fer). It has become increasingly apparent In the past few years that no one scheme controls the useof iron in the biological world—except that reduction of Fe3+ to Fe2+ may be the single most important factor. Other interactions with Fe2+ discussed are: K, Mn, N, HCO‐ 3, and reduction of Fe to Fe by ultra violet light.

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