Abstract
The uptake of 59Fe from FeCl3, ferric (Fe3+) citrate (FeCitr) and Fe3+-EDTA (FeEDTA) was studied in leaf mesophyll of Vigna unguiculata (L.) Walp. Uptake rates decreased in the order FeCl3>FeCitr≫FeEDTA, and uptake depended on an obligatory reduction step of Fe3+ to Fe2+, after which the ion could be taken up independently of the chelator, citrate. Uptake was strongly increased by photosynthetically active light (λ>630 nm), and kinetic analysis revealed saturation kinetics with a K m (FeCitr) of 80–110 μM. In the presence of an external Fe2+ scavenger, bathophenanthroline disulfonate, the mesophyll also reduced external FeCitr with a K m of approx. 50–60 μM. The reduction rates for FeCitr were five-to eightfold higher than necessary for uptake. Purified plasma membranes from leaves revealed an NADH-dependent FeCitr- and FeEDTA-reductase activity, which had a pH optimum of 6.5–6.8 and a K m of approx. 20 μM for NADH. Under anaerobic conditions, a K m of 130–170 μM for ferric chelates was obtained, while in the presence of oxygen a K m (FeCitr) of approx. 100 μM was found. It is concluded that the leaf plasma membrane provides a ferric-chelate-reductase activity, which plays a crucial role in iron uptake of leaf cells. Under in-vivo conditions, however, reactive oxygen species or strong (blue) light may also contribute to the obligatory reduction of Fe3+ prior to uptake.
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Abbreviations
- BPDS:
-
bathophenanthroline disulfonate
- DCMU:
-
3-(3,4 dichlorophenyl)-1,1-dimethyl urea
- FCR:
-
ferricchelate reductase
- FeCitr:
-
Fe3+-citrate
- FeEDTA:
-
Fe3+-EDTA
- PM:
-
plasma membrane
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This work was supported by the SCIENCE program of the European Community (contract no. SC1000344; P.R.M.). We wish to thank P. Siersma and C. Winter for their cooperation at the Central Isotope Laboratory of the Biological Centre of the University of Groningen.
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Brüggemann, W., Maas-Kantel, K. & Moog, P.R. Iron uptake by leaf mesophyll cells: The role of the plasma membrane-bound ferric-chelate reductase. Planta 190, 151–155 (1993). https://doi.org/10.1007/BF00196606
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DOI: https://doi.org/10.1007/BF00196606