Journal Article

Technical Advance: Reduction of Fe(III)-Chelates by Mesophyll LeafDisks of Sugar Beet. Multi-Component Origin and Effects of FeDeficiency

Ajmi Larbi, Fermín Morales, AnaFlor López-Millán, Yolanda Gogorcena, Anunciación Abadía, PetraR. Moog and Javier Abadía

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 42, issue 1, pages 94-105
Published in print January 2001 | ISSN: 0032-0781
Published online January 2001 | e-ISSN: 1471-9053 | DOI: https://dx.doi.org/10.1093/pcp/pce012
Technical Advance: Reduction of Fe(III)-Chelates by Mesophyll LeafDisks of Sugar Beet. Multi-Component Origin and Effects of FeDeficiency

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The characteristics of the Fe(III)-chelate reductase activity have been investigated in mesophyll disks of Fe-sufficient and Fe-deficient sugar beet leaves. The Fe(III)-chelate reductase activity of mesophyll disks was light dependent and increased markedly when the epidermis was removed. Iron(III)-citrate was photo-reduced directly by light in the absence of plant tissue. Total reductase activity was the sum of enzymatic mesophyll reduction, enzymatic reduction carried out by organelles exposed at the disk edge and reduction caused by the release of substances both by exposed mesophyll cells and at the disk edge. Compounds excreted were shown by HPLC to include organic anions, mainly oxalate, citrate and malate. When expressed on a leaf surface basis, Fe deficiency decreased the total mesophyll Fe(III)-chelate reductase activity. However, Fe-sufficient disks reduced less Fe than the Fe-deficient ones when expressed on a chlorophyll basis. The optimal pH values for Fe(III) reduction were always in the range 6.0–6.7. In control leaves Fe(III)-citrate and Fe(III)-malate were the substrates that led to the highest Fe reduction rates. In Fe-deficient leaves Fe(III)-malate led to the highest Fe reduction rates, followed by Fe(III)-EDTA and then Fe(III)-citrate. Km values for the total reductase activity, enzymatic mesophyll reduction and enzymatic reduction carried out by organelles at the disk edge were obtained.

Keywords: Key words: Beta vulgaris — Iron deficiency — Iron reduction — Mesophyll — Sugar beet.; Abbreviations: FC-R, ferric chelate-reductase; PM, plasma membrane; PDTS, 3-(2-pyridyl)-5,6-bis(4-phenylsulfonic acid)-1,2,4-triazine; PPFD, photosynthetic photon flux density; Rec and Rem, Fe reduction due to enzymatic processes at the cut edge and at the mesophyll cell plasma membrane, respectively; Rlc and Rlm, Fe reduction due to compounds released from the leaf disk cut edge and undamaged exposed mesophyll cells, respectively; SPAD, portable leaf Chl meter; Tr, total Fe reduction by leaf disks.

Journal Article.  7183 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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