Iron‐Stress Response in Tomato (Lycopersicon esculentum) 1. Sites of Fe Reduction, Absorption and Transport

Abstract

T3238fer (Fe-inefficient) and T3238FER (Fe-efficient) tomato plants differ in their ability to utilize Fe and therefore can be used as test genotypes to locate sites of Fe uptake or to characterize changes that occur in roots in response to Fe stress (Fe deficiency). T3238fer does not respond to Fe stress. Release of hydrogen ions and reduction of Fe^+ to Fe^+ are two primary responses of T3238FER roots to Fe stress. Fe reduction sites were predominately in the young lateral roots, and between the regions of root elongation and maturation of the primary root. The use of BDPS (bathophenanthrolinedisulfonate) to trap Fe^+ did not affect the release of H+ ions or reduction by T3238FER roots. BPDS did not decrease Fe uptake until it exceeded the Fe concentration in the nutrient solution. A sevenfold increase in BPDS caused a threefold decrease in Fe taken up by the plant. Fe^+ is reduced to Fe^+ at root sites accessible to BPDS. Adding Zn decreased the response to Fe stress.Iron stress initiates the development of lateral roots, and we propose that most Fe enters the plant through these roots. The iron moves through protoxylem into the metaxylem of the primary root and then to the top of the plant as Fe citrate. Root environmental factors that are competitive or inhibit Fe-stress response, or genotypes that fail to respond to Fe stress, contribute to the development of Fe deficiency in plants.

Iron Nutrition of Peanut Enhanced by Mixed Cropping with Maize: Possible Role of Root Morphology and Rhizosphere Microflora

“…Moreover, roots of peanut in mixture with maize produced more lateral roots than those grown in monoculture. The root tip regions of young lateral roots have been reported to be more active than other root areas in Fe reduction [20] and proton extrusion. [21,22] It is therefore conceivable that the higher exudation of Fe-reducing and Fe-chelating compounds by peanut roots reported here may have been concomitant with greater root branching and=or a larger production of lateral roots for plants in mixed culture.…”

The tomato fer gene encoding a bHLH protein controls iron-uptake responses in roots

“…The most promising clues on the regulation of strategy I are expected from the identification of the fer gene. The fer (T3238fer) mutant is not able to switch on strategy I responses after iron deficiency, such as enhanced extrusion of protons and Fe(III)-chelate reductase activity in the root (15,16). Reciprocal grafting of the mutant to a wild type indicated that the fer gene is required in roots but not in shoots (15).…”

Differential Regulation of nramp and irt Metal Transporter Genes in Wild Type and Iron Uptake Mutants of Tomato

“…A promising clue about signaling components involved in iron acquisition was recently derived from the molecular identification of the tomato fer gene encoding a root-specific bHLH protein (25). The tomato fer mutant is unable to develop physiological and morphological iron-deficiency responses such as iron reduction and induced Leirt1 transporter gene expression in roots and accumulates less iron than wild type, leading to severe chlorosis (25)(26)(27). The fer gene seems to be required for sensing iron availability in the root tip and subsequently regulating the appropriate physiological and morphological responses (25).…”