Arbuscular mycorrhizal fungi and tolerance of Fe stress in plants

Abstract

Iron (Fe), an essential micronutrient for plant growth, has many important physiological and biochemical functions in plants, whereas Fe deficiency frequently occurred especially in calcareous and/or alkaline soils with high HCO3 - and/or pH levels which easily generate slightly soluble Fe(III) compounds. Fe deficiency is usually characterized by chlorosis, which is an important indicator of the decreased chlorophyll level in leaf and mainly attributed to lower Fe uptake confined by Fe solubility in soils. Arbuscular mycorrhizal fungi (AMF), one of the soil beneficial microorganisms, represented positive contributions to soil nutrient uptake, especially in P-deficient soils, as well as alleviate the harmful effects of Fe deficiency. This review outlined the effects of AMF on Fe uptake, chlorophyll contents, photosynthesis, and Fe storage in glomalin under Fe stress. Plants have evolved two strategies for Fe uptake under Fe deficiency conditions, viz., Fe(III)-chelate reductase (FCR) and phytosiderophore (PS). AMF-inoculated plants have shown greater tolerance to Fe stress (Fe deficiency), which may be due to (1) the improved Fe uptake through direct absorption by extra-radical hyphae and (2) the Fe mobilization by increasing root FCR activities and decreasing soil pH value of mycorrhizal plants, thus resulting in higher Fe and chlorophyll contents, better photosynthetic performances, and higher plant biomass, but lower leaf chlorosis. Besides, glomalin released by mycorrhizas potentially participates in Fe availability and transferability in the mycorrhizosphere, but the underlying mechanisms need to be further analyzed.