IRON REQUIREMENT FOR AND EFFECTS OF PROMOTERS AND INHIBITORS OF ETHYLENE ACTION ON STIMULATION OF FE(III)-CHELATE REDUCTASE IN ROOTS OF STRATEGY-I-SPECIES

Stimulation of root Fe(III) reductase activity by iron additions to ir on-deficient growth media may be the result of iron activation of 1-am inocyclopropane-1-carboxylic acid (ACC) oxidase required for ethylene biosynthesis. Two different ethylene inhibitors, aminooxyacetic acid ( AOA) (20 mu M; ACC synthase inhibitor) and cobalt (3 mu M CoCl2; ACC o xidase inhibitor), were used to study the effects of iron supply and c obalt inhibition on ethylene action in controlling the activity of Fe( III)-chelate reductase in pea (Pisum sativum L.) roots, Supplying 20 m u M e(III)-N,N'-ethylenebis[2-(2-hydroxypheyl)-glycine [Fe(III)-EDDHA] to either cobalt-treated, iron-deficient Sparkle (normal parent) or E 107 (brz mutant genotype) pea seedlings reversed the negative effects of cobalt on root Fe(III)-reductase activity, Re-supplying 20 mu M Fe( III)-EDDHA to iron-deficient, AOA-treated seedlings did not enhance ro ot (Fe(III)-reductase, Apparently, cobalt competes with iron for the a ctive site in ACC oxidase during ethylene synthesis, Inhibition of roo t reductase activity by cobalt treatment lowered manganese, zinc, magn esium and potassium content of mutant E107 pea seedlings, In contrast, iron enhancement of root reductase activity in iron-deficient, cobalt -treated E107 seedlings resulted in higher seedling accumulations of m anganese, zinc, magnesium and potassium, These results support the hyp othesis that root cell plasma membrane reductase activity plays a role in cation uptake by root cells.