Strategies of plants for acquisition of iron

Abstract

Two different types of root response to Fe deficiency (strategies) have been identified in species of the Plant Kingdom. In Strategy I which occurs in all plant species except grasses, a plasma membrane-bound reductase is induced with enhanced net excretion of protons. Often the release of reductants/chelators is also higher. In Strategy II which is confined to grasses, there is an increase in the biosynthesis and secretion of phytosiderophores which form chelates with Fe It1. Uptake of Fe Iu phytosiderophores is mediated by a specific transporter in the plasma membrane of root cells of grasses. From results based mainly on long-term studies under non-axenic conditions this classification into two strategies has been questioned, and the utilization of Fe from microbial siderophores has been considered as an alternative strategy particularly in grasses. Possible reasons for controversial results are discussed in some detail. The numerous effects of microorganisms in non-axenic cultures, and the as yet inadequate characterization of the so-called standard (basic) reductase present major limitations to understanding different mechanisms of Fe acquisition. In comparison with the progress made in identifying the cellular mechanisms of root responses in Strategy I and Strategy II plants, our understanding is poor concerning the processes taking place in the apoplasm of root rhizodermal cells and of the role of low-molecular-weight root exudates and siderophores in Fe acquisition of plants growing in soils of differing Fe availability.

Effect of excess iron and copper on physiology of aquatic plant Spirodela polyrrhiza (L.) Schleid

“…Though iron and copper are essential trace elements for plants, being involved in many processes of metabolisms (Brown, 1978;Geider and Laroche, 1994;Marschner and Romheld, 1994), excess concentration can result in toxicity, especially in altering chromatin structure, synthesis of chlorophyll and protein, enzyme activity, photosynthesis and respiration, water content and plant biomass yield (Guerinot and Yi, 1994;Mori, 1999;Olaleye et al, 2001;Connolly and Guerinot, 2002;Burzynski and Klobus, 2004).…”

Review on iron availability in soil: interaction of Fe minerals, plants, and microbes

“…Many aerobic microbes depend critically on their metabolites for the synthesis of these compounds Phillips 1986, 1988 For what concerns plants, to acquire Fe for their metabolism and growth, they have evolved active uptake mechanisms that differ between dicots (including also non-graminaceous monocots) and monocots (see also the review of Kobayashi and Nishizawa 2012). In the first case, the micronutrient is acquired by a reduction-based Fe uptake mechanism (strategy I, Marschner and Römheld 1994), which involves two steps: a reduction of Fe III to Fe II and an intake of Fe II . When Fe is limiting, the response of these plants includes the induction, in a coordinated form, of the Fe III -reduction activity at the root surface and the Fe II transport across the root epidermal cell membrane (Connolly et al 2003).…”

Sensitivity to and requirement for iron in Plantago species

“…Higher plants can mobilize Fe pools of low solubility by adaptive changes in root morphology (Landsberg, 1982 ;Rosenfield, Reed & Kent, 1991) and physiological reactions that affect the availability of Fe at the roots. In dicotyledonous and non-grass monocotyledonous plants, these responses include acidification of the rhizosphere, enhanced reduction of ferric chelates and release of reducing and\or chelating low-molecular-weight compounds (Strategy I, Marschner & Ro$ mheld (1994)). Adaptation to high Fe concentrations might be achieved by Fe-excluding mechanisms such as reoxidation of Fe# + and concomitant precipitation or internal detoxification (Bienfait, 1989).…”

“…Based on temporal and spatial expression of its components, the Strategy I response has been defined as a co-operative response to suboptimal Fe availability (Marschner & Ro$ mheld, 1994). However, the various components such as Fe(III) reductase activity and enhanced proton extrusion might be regulated separately (Schmidt & Bartels, 1996 ;Yi & Guerinot, 1996) and their relative importance might differ between species (Marschner & Ro$ mheld, 1994).…”

“…However, the various components such as Fe(III) reductase activity and enhanced proton extrusion might be regulated separately (Schmidt & Bartels, 1996 ;Yi & Guerinot, 1996) and their relative importance might differ between species (Marschner & Ro$ mheld, 1994). Iron-deficiency-induced proton extrusion has been observed exclusively in P. major, suggesting that acidification of the rhizosphere is of minor importance in Plantago.…”