SPATIAL AND TEMPORAL DEVELOPMENT OF IRON(III) REDUCTASE ACTIVITY IN ROOT SYSTEMS OF PISUM SATIVUM (FABACEAE) CHALLENGED WITH IRON‐DEFICIENCY STRESS

The development of plasma membrane‐associated iron(III) reductase activity was characterized in root systems of Pisum sativum during the first 2 wk of growth, as plants were challenged with iron‐deficiency stress. Plants of a parental genotype (cv. Sparkle) and a functional iron‐deficiency mutant genotype (E107) were grown hydroponically with or without supplemental iron. Iron(III) reductase activity was visualized by placing the roots in an agarose matrix containing 0.2 idm Fe(III)‐ethylenediaminetetraacetic acid and 0.3 mM Na 2 ‐bathophenanthrolinedisulfonic acid (BPDS). Red staining patterns, resulting from the formation of Fe(II)‐BPDS, were used to identify iron(III)‐reducing regions. Iron(III) reduction was extensive on roots of E107 as early as d 7, but not until d 11 for ‐Fe‐treated Sparkle. Roots of +Fe‐treated Sparkle showed limited regions of reductase activity throughout the period of study. For secondary lateral roots, iron(III) reduction was found for all growth types except + Fe‐treated Sparkle. Treating Sparkle plants alternately to a cycle of iron deficiency, iron sufficiency, and iron deficiency revealed that reductase activity at a given root zone could be alternatively present, absent, and again present. Our results suggest that for Pisum roots grown under the present conditions, iron‐deficiency stress induces the activation of iron(III) reductase capacity within 2 d.