DETERMINATION OF THE COPPER-2+ ACTIVITY REQUIRED BY MAIZE USING CHELATOR-BUFFERED NUTRIENT SOLUTIONS

Hydroponics is a useful method to study micronutrient deficiencies in plants. Problems in using this method to study Cu deficiencies are: (i) control of Cu supply to induce any degree of deficiency is difficult, (ii) purification of reagents is required to induce severe deficiency; and (iii) when chelators are added to induce Cu deficiency, the chelators may inactivate Fe, making Fe unavailable to plants. Mild to severe Cu deficiencies were induced in maize (Zea mays L.) without the purification of reagents using chelators HEDTA [N-(2-hydroxyethyl) ethylenediamine triacetate] with and without BPDS (4, 7- diphenyl- 1, 10- phenanthrolinedisulfonic acid) to bind and inactivate Cu. GEOCHEM-PC was used to calculate the quantity of free and chelate-bound Cu. A wide range in leaf and root Cu concentrations was observed from plants grown in HEDTA solutions with calculated solution Cu2+ activities of 10(-15.4) to 10(-12.4) M. The calculated Cu2+ activity associated with a 20% reduction in yield was 10(-14.5) M (control plants yielded 15 g dry matter at 18 d). Solutions containing HEDTA with BPDS and the lowering of nutrient-solution Ca concentrations were evaluated as means of inducing severe Cu deficiency. Maize grown in BPDS-added solutions were severely stunted regardless of Ca treatment, and had significantly lower shoot Cu, Mn, and Fe concentrations than those found in other treatments. Results indicated Cu availability to maize was controlled by Cu2+ and not Cu+ activity. HEDTA, especially in combination with BPDS, can effectively induce Cu deficiency and supply adequate Fe to maize.