Influence of bicarbonate and metal ions on the development of root Fe(III) reducing capacity by Fe-deficient cucumber (Cucumis sativus) plants

The effect of bicarbonate and selected metal ions on the development of enhanced root Fe(III) reducing capacity (a response to Fe deficiency of dicotyledons) was studied in young plants of cucumber ( Cucumis sativus L. cv. Ashley) grown in nutrient solution. Pretreatment of 11-day-old Fe-deficient cucumber plants with 20 m M NaHCO₃, for at least 23 h prior to determination of root Fe(III) reducing capacity, markedly inhibited this response. The inhibitory effect of bicarbonate could be partly reversed by a 4- to 8-h treatment with either 10 μ M MnSO₄, 10 μ M FeEDDHA, 2 μ M ZnSO₄, 0.5 μ M NiCl₂, or 0.25 μ M , or CoSO₄ (final concentrations), added to the nutrient solution. By contrast, the addition of other salts of metal ions, like CuSO₄ and Cd(NO₃)₂, at 0.25, 0.5 or 1 μ M , or MgSO₄, at 0.5, 1 or 2 m M (final concentrations), had no beneficial effect. The results suggest that bicarbonate may inhibit the development of root Fe(III) reducing capacity by diminishing the availability of certain metal ions required for this response.