PHYSIOLOGICAL CHARACTERIZATION OF A SINGLE-GENE MUTANT OF PISUM-SATIVUM EXHIBITING EXCESS IRON ACCUMULATION .1. ROOT IRON REDUCTION AND IRON UPTAKE

Root systems of mutant (E 107) and parental (cv 'Sparkle') Pisum sativum genotypes were studied to determine the basis for excess Fe accumulation in E107. Plants were grown with (+Fe-treated) or without (-Fe-treated) added Fe(III)-N,N'-ethylenebis[2-(2-hydroxyphenyl)glycine] in aerated nutrient solutions. Daily measurements of Fe(III) reduction indicated a four- to sevenfold higher reduction rate in +Fe- or -Fe-treated E107, and -Fe-treated Sparkle, when compared with +Fe-treated Sparkle. An agarose-based staining technique used to localize Fe(III) reduction, revealed Fe(III) reduction over most of the length of the roots (but not at the root apices) in both E107 treatments and -Fe-treated Sparkle. In +Fe-treated Sparkle, Fe(III) reduction was either nonexistent or localized to central regions of the roots. Measurements of short-term Fe influx (with 0.1 millimolar 59Fe(III)-ethylenediaminetetraacetic acid) was also enhanced (threefold) in +Fe- or -Fe-treated E107 and -Fe-treated Sparkle, relative to +Fe-treated Sparkle. The physiological characteristics of E107 root systems, which are similar to those seen in Fe-deficient Sparkle, have led us to conclude that the mutation causes E107 to act functionally as an Fe-deficient plant, and appears to explain the excess Fe accumulation in E107.