Iron uptake by leaf mesophyll cells: The role of the plasma membrane-bound ferric-chelate reductase

Abstract

Abstract. The uptake of 59Fe from FeC13, ferric (Fe 3+) citrate (FeCitr) and Fe3+-EDTA (FeEDTA) was studied in leaf mesophyll of Vigna unguiculata (L.) Walp. Uptake rates decreased in the order FeC13 > FeCitr>> FeEDTA, and uptake depended on an obligatory reduction step of Fe 3+ to Fe 2+, after which the ion could be taken up independently of the chelator, citrate. Uptake was strongly increased by photosynthetically active light (2 > 630 nm), and kinetic analysis revealed saturation kinetics with a K m (FeCitr) of 80-110 laM. In the presence of an external Fe 2+ scavenger, bathophenanthroline disulfonate, the mesophyll also reduced external FeCitr with a K m of approx. 50--60 laM. The reduction rates for FeCitr were fiveto 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 laM for NADH. Under anaerobic conditions, a K m of 130-170 laM, for ferric chelates was obtained, while in the presence of oxygen a K m (FeCitr) of approx. 100 laM 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 Fe 3+ prior to uptake.

Expression Profiles of Arabidopsis thaliana in Mineral Deficiencies Reveal Novel Transporters Involved in Metal Homeostasis

“…While FRO2 was not expressed in leaves, FRO3 was increased under iron defi- ciency both in the roots and in the leaves. The increase in leaf-localized FRO3 shows that reduction of ferric iron to ferrous is also a component of metal transport in the leaves (Table IIA) (34). Iron deficiency also led to decreased expression of ferritin genes in roots (AtFer1) and leaves (AtFer1 and AtFer4) (Table IIC).…”

Phytotranslocation of Fe by biodiesel plant Jatropha curcas L. grown on iron rich wasteland soil

“…While the molecular mechanisms involved in iron transport into leaf cells remain unclear (Hell and Stephan, 2003). It has been reported that ferric chelate reductase activity is detectable in leaves of sunflower (Guardia and Alcantara, 1996) and Vigna unguiculata (Bruggemann et al, 1993). A recent study examined the fractionation of stable iron isotopes taken up from the soil in various aerial portions of bean, pea, soybean, maize, oat, wheat etc (Guelke and Von Blanckenburg, 2007).…”

Iron: Nutritious, Noxious, and Not Readily Available

“…Uptake of Fe(II1) by leaf mesophyll appears to depend on a reduction step via a PMbound Fe(lI1) chelate reductase, which most likely releases Fe(I1) from Fe(II1) citrate (Briiggemann et al, 1993). There is also some evidence that Fe(II1) reduction in vivo may be aided by intermediate superoxide radical formation or by strong blue light (Briiggemann et al, 1993). We know very little about the movement of iron in the phloem sap.…”