Chelator-buffered nutrient solutions have been used extensively in studying plant-micronutrient relationships, but the effects of the chelator on plants are poorly understood. This study compared responses to Zn deficiency of two wheat genotypes (Triticum aestivum, cv. Aroona, and T. turgidum L. conv. durum, cv. Durati) grown in conventional and chelator-buffered nutrient solutions. With the same low activity of Zn2+ in both types of solution. shoot growth was impaired more and root exudation of phytosiderophores was greater in the chelator-buffered than in the conventional solution. Under Zn deficiency. Durati wheat (sensitive to Zn deficiency) suffered a greater level of inhibition of shoot growth and exuded less phytosiderophores from roots than Aroona a heat (tolerant to Zn deficiency). Under both Zn deficiency and Zn sufficiency, a greater concentration and content of Zn and Fe in the shoots and Cu in the roots were found in plants grown in the conventional rather than in the chelator-buffered solutions. In contrast. accumulation of Mn was greater in the roots of plants grown in the chelator-buffered than in the conventional solution. The rate of Zn and Fe transport to the shoots was greater in the plants grown in the chelator-buffered compared to the conventional solution. It is concluded that Zn deficiency is mure severe in the chelator-buffered than in the conventional solution, even with the calculated Zn2+ activity being the same in both types of solution. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.