Mechanism of iron reduction by roots of Phaseolus vulgaris L.

Sijmons, Peter C.; Bienfait, H. Frits

doi:10.1080/01904168409363233

Cited by 11 publications

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Section: Introductionmentioning

confidence: 99%

“…The enzyme involved should be capable ofelectron transfer across the plasma membrane. We demonstrated that cytosolic reduced pyridine nucleotides are the direct electron donors for this enzyme (14,15).Plants suffering from iron deficiency show a considerable increase in their Fe"' reduction capacity at the root surface (6, 12). We established that the potential supply of reduced pyridine nucleotides is greatly enhanced under iron deficiency and that the level of cytosolic NAD(P)H is strongly lowered when irondeficient roots are exposed to extracellular Fe"' salts (14).…”

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Cytosolic NADPH Is the Electron Donor for Extracellular Fe^III Reduction in Iron-Deficient Bean Roots

Sijmons

Briel²,

Bienfait³

1984

Plant Physiol.

153

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Pyridine nucleotides were determined in lateral roots of iron-deficient and iron-sufficient Phaseolus vulgaris L. cv Prelude. In iron-deficient plants, total NADP per gram fresh weight and the NADPH/NADPI ratio were twice the values found in iron-sufficient plants. The NADPH/ NADP ratio in iron-deficient plants was considerably lowered after a 2 minute incubation in I millimolar ferricyanide. Total NAD was not influenced by growth conditions and was mainly present in oxidized form.These results indicate that NADPH is the electron donor for the high Fe"' reduction activity found in iron-deficient roots, a process that is part of the Fe-uptake mechanism.The reduction of Fe"' to Fe" is an essential step in the uptake of iron by roots of dicotyledonous plants (6). Evidence is accumulating that this reduction takes place at the plasma membrane of root cells by an enzymic process (1,3,4,13,14). The enzyme involved should be capable ofelectron transfer across the plasma membrane. We demonstrated that cytosolic reduced pyridine nucleotides are the direct electron donors for this enzyme (14,15).Plants suffering from iron deficiency show a considerable increase in their Fe"' reduction capacity at the root surface (6, 12). We established that the potential supply of reduced pyridine nucleotides is greatly enhanced under iron deficiency and that the level of cytosolic NAD(P)H is strongly lowered when irondeficient roots are exposed to extracellular Fe"' salts (14). We set out to determine more precisely the electron donor for extracellular Fe"' reduction. Through direct measurements of pyridine nucleotides in root extracts, we demonstrate that NADPH is the source of electrons for the membrane-bound enzyme system, of which the activity is stimulated by iron deficiency. (17), the Mn concentration in the iron-free nutrient solution was lowered from 9 to 0.9 uM. The solutions were replaced with freshly prepared nutrient solution on the 3rd, 6th, and 8th d after transfer and the plants were used for experiments on the 8th or 9th d. The plants were grown in a growth chamber (16 h light, 22C) under 26 w m 2 (Philips TL 33 fluorescent) and 65% RH. MATERIALS AND METHODSIsolation and Pretreatment of Lateral Roots. For each experiment, about 20 g (fresh weight) lateral roots of 2 to 5 cm length were isolated from 30 plants. Isolated lateral roots were kept in aerated iron-free nutrient solution at room temperature until all roots were harvested (about 2 h). The nutrient solution was decanted and the roots were gently blotted with tissue paper and weighed. They were then quickly divided into four equal portions (on fresh weight basis) and returned to aerated iron-free nutrient solution for 10 min. After this preincubation, two portions were incubated in 1 mM K3Fe(CN)6 for 2 min at room temperature. The nutrient solutions of all four portions were then decanted and the roots were immediately frozen in liquid N2 and homogenized with mortar and pestle. To one untreated and one ferricyanide-treated portion, a fixed amount of the p...

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Section: Introductionmentioning

confidence: 99%

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confidence: 99%