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Plant Physiology 87:167-171 (1988)
© 1988 American Society of Plant Biologists

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Environmental and Stress Physiology

Characterization of Phloem Iron and Its Possible Role in the Regulation of Fe-Efficiency Reactions

Frank M. Maas1, Dirk A. M. van de Wetering, Marinus L. van Beusichem and H. Frits Bienfait2

Plantenfysiologisch Laboratorium, Universiteit van Amsterdam, Kruislaan 318, 1098 SM Amsterdam, Vakgroep Bodemkunde en Plantevoeding, Landbouwuniversiteit Wageningen, PB 8005, 6700 EC Wageningen, The Netherlands

`Fe-efficiency reactions' are induced in the roots of dicotyledonous plants as a response to Fe deficiency. The role of phloem Fe in the regulation of these reactions was investigated. Iron travels in the phloem of Ricinus communis L. as a complex with an estimated molecular weight of 2400, as determined by gel exclusion chromatography. The complex is predominantly in the ferric form, but because of the presence of reducing compounds in the phloem sap, there must be a fast turnover in situ between ferric and ferrous (k {approx} 1 min–1). Iron concentrations in R. communis phloem were determined colorimetrically or after addition of 59Fe to the nutrient solution. The iron content of the phloem in Fe-deficient plants was lower (7 micromolar) than in Fe-sufficient plants (20 micromolar). Administration of Fe-EDTA to leaves of Phaseolus vulgaris L. increased the iron content of the roots within 2 days, and decreased proton extrusion and ferric chelate reduction. The increase in iron content of the roots was about the same as the difference between iron contents of roots grown on two iron levels with a concomitantly different expression of Fe-efficiency reactions. We conclude that the iron content of the leaves is reflected by the iron content of the phloem sap, and that the capacity of the phloem to carry iron to the roots is sufficient to influence the development of Fe-efficiency reactions. This does not preclude other ways for the shoot to influence these reactions.

1 Present address: Centrum voor Agrobiologisch Onderzoek, PB 14, 6700 AA Wageningen, The Netherlands.

2 Present address: Oudegracht 285, 3511 PA Utrecht, The Netherlands.




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Copyright © 1988 by the American Society of Plant Biologists