ROOT-MEDIATED FERRIC REDUCTION - RESPONSES TO IRON-DEFICIENCY, EXOGENOUSLY INDUCED CHANGES IN HORMONAL BALANCE AND INHIBITION OF PROTEIN-SYNTHESIS

The effects of the auxin analogue 2,4-dichlorophenoxyacetic acid (2,4-D), the translation inhibitor cycloheximide (CHM) and iron deficiency on electron transport activities in roots have been investigated. Deprivation of an external Fe supply caused an increase in capacity to reduce both FeEDTA and the artificial electron acceptor ferricyanide. With respect to the iron stress-induced redox activity, bean (Phaseolus vulgaris L.) roots reduced both substrates at equal rates, while roots of Plantago lanceolata L. exhibited clearly higher rates with FeEDTA. The iron stress-induced FeEDTA and ferricyanide reduction activities were unequally affected by CHM in both species, reflecting the differences in substrate specificity. Application of 2,4-D via the nutrient solution induced an increase in ferricyanide reduction rates in iron-sufficient roots of P. lanceolata; the reduction of FeEDTA was only slightly affected. The presence of 2,4-D caused no further enhancement in reduction activity of plants grown without Fe. However, iron-deficient plants exhibited a distinct developmental pattern of ferric reduction activities when treated with 2,4-D, resembling the development of 2,4-D-induced ferricyanide reduction by iron-sufficient plants. This information is taken as support that the reduction of ferricyanide and FeEDTA can in part be separately regulated. The data also seem to indicate that the amount of Fe2+ is the main cause for induction or repression of ferric chelate reduction by roots of iron-efficient plants.