The physiology of micronutrient homeostasis in field crops

Iron homeostasis related genes in rice

“…The mechanism based on 492 Gross et al the release of phytosiderophores for Fe +3 chelation and uptake under mineral deficiency represents an evolutionary advantage relative to the mechanism of strategy I, since the latter requires an energy dependent reduction step prior to the uptake (Grusak et al, 1999). Presumably, grasses acquired the strategy II components in addition to those of strategy I, which progressively assumed a more secondary role in mineral uptake and transport.…”

“…The YS1 protein, for example, transports Fe 3+ phytosiderophores, and possibly Fe +2 NA , structurally similar to phytosiderophores. Another important mineral carrier in plants is citrate, mainly associated with iron transport in the xylem (Grusak et al, 1999). Since members of the YS family were unable to transport citrate-complexed minerals , it may be possible that NRAMP or ZIP members could transport such complexes.…”

Revisiting the Metal-Binding Chemistry of Nicotianamine and 2′-Deoxymugineic Acid. Implications for Iron Nutrition in Strategy II Plants

“…Norvell et al, 1993), the redox activity of a given Fe III complex can be computationally assessed by considering the sum of following three reactions: When combined with the appropriate log K for the second reaction (12.5 at I ϭ 0.1 m; Morel and Hering, 1993), followed by conversion to E H notation, the corresponding constants for the net reaction are 0.278, 0.089, and 0.053 V for NA, EDTA, and DMA, respectively. As with any so-ordered ranking of standardized redox potentials, the higher E H value for NA implies that its Fe III complex is a comparatively good oxidant, and thus more readily reduced by strong reductants such as NAD(P)H (Morel and Hering, 1993 (Romheld and Marschner, 1986;Grusak et al, 1999), NA and DMA might compete for Fe III in the cytoplasm, and von Wirén et al (1999) suggested the transfer of Fe III from DMA to NA upon entry into the cytoplasm. However, inclusion of the Fe III -DMA(H Ϫ1 ) Ϫ complex in the chemical modeling implies that Fe III would remain approximately 100% complexed to DMA in the cytoplasm.…”

“…Deoxymugineic acid is representative of the family of phytosiderophores that are excreted by Strategy II species into the rhizosphere in response to Fe deficiency (Ma and Nomoto, 1996). Phytosiderophores increase the solubility of Fe III by chelation, and are absorbed as the intact Fe III ligand by Strategy II plants (Romheld and Marschner, 1986;Grusak et al, 1999).…”

Characterization of 68Zn uptake, translocation, and accumulation into developing grains and young leaves of high Zn-density rice genotype

“…To increase Zn uptake by roots, the Zn availability in the rhizosphere must be increased (Welch, 1995), which can be performed by enhanced release rates of root-cell H + , metal chelating compounds and/or reductants, by increasing root absorptive surface area (fine roots and root hairs), and by association with mycorrhizal fungi (Liu et al, 2000;Ryan and Angus, 2003;Gao et al, 2007). However, knowledge on Zn transport in rice plant is scant (Grusak et al, 1999;Rengel, 1999). Zn transport in plants takes place through both the xylem and the phloem.…”