PHYTOSIDEROPHORE RELEASE BY SORGHUM, WHEAT, AND CORN UNDER ZINC-DEFICIENCY

Zinc (Zn) deficiency is more common in corn (Zea mays L.) than in sorg hum [Sorghum bicolor (L.) Moench] or wheat (Triticum sp.). The ability of wheat to withstand low soil Zn conditions is related to increased release of phytosiderophore from its roots. The reasons for sorghum's ability and corn's inability to utilize low levels of soil Zn have not been explored adequately. The objectives of this research were to 1) ascertain if Zn deficiency could be induced in sorghum, wheat, and cor n grown in a chelator-buffered nutrient solution and 2) determine rela tive releases of phytosiderophore from roots of sorghum, wheat, and/or corn under Zn-deficiency conditions. Sorghum, wheat, and corn were gr own hydroponically in the greenhouse with a chelator-buffered nutrient solution designed to induce Zn deficiency, while supplying adequate a mounts of other nutrients. Root exudates were collected over time to m easure phytosiderophore release. Shoot Zn concentrations and shoot and root dry matter yields were determined also. The technique was effect ive for inducing Zn deficiency in sorghum, wheat, and corn, as evidenc ed by reduced shoot and root dry matter yields, shortened internodes, reduced shoot Zn concentrations, and plant Zn concentrations below the suggested critical values for these species. Sorghum and wheat plants increased the release of phytosiderophore in response to Zn deficienc y, but corn did not. The total amount of phytosiderophore released by the roots was in the order wheat>sorghum>corn. The absence of a ''phyt osiderophore'' response to Zn deficiency of corn, coupled with the evi dence that this species requires, or at least accumulates, more Zn tha n wheat or sorghum, provides an explanation as to why Zn deficiencies are more prevalent for corn than wheat or sorghum under field conditio ns.