Efect of zinc and iron deficiency on phytos1derophore release in wheat genotypes differing in zinc efficiency

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Abstract
The effect of varied zinc (Zn) and iron (Fe) supply on the release of Zn and Fe mobilizing phytosiderophores from roots was studied in Zn‐efficient Aroona and Zn‐inefficient Durati wheat genotypes (Triticum aestivum cv. Aroona; T. durum cv. Durati) grown under controlled environmental conditions in nutrient solution for 25 days. Phytosiderophore release was determined by the measurement of Zn and Fe mobilizing capacity of root exudates from a Zn‐loaded resin and from freshly precipitated FeIII hydroxide as well as identification by HPLC analysis. Visual Zn‐deficiency symptoms, such as necrotic patches on leaves and reduction in shoot length, appeared first and more severely in Zn‐inefficient Durati, although the concentrations of total Zn in shoot and root tissues were the same in both genotypes. Zinc‐efficient Aroona responded to Zn deficiency by increasing phytosiderophore release usually after 10 days growth in nutrient solution, whereas the phytosiderophore release in Durati remained at a very low level during 25 days growth. In contrast, under Fe deficiency and also under both Fe and Zn deficiency, Aroona and Durati released similarly high amounts of phytosidero‐ phores. HPLC analysis of root exudates revealed that the same phytosiderophores were released under Zn as under Fe deficiency, 2'‐deoxymugineic acid (DMA) being the dominant phytosiderophore. Besides DMA, 3‐hydroxymugineic acid (HMA) could also be identified mainly, however, in root exudates of Zn and of Fe‐deficient Aroona. In Zn‐deficient Durati, both DMA and HMA were released in much lower amounts. The results demonstrate that phytosiderophore release can occur under Zn deficiency as well as under Fe deficiency, and enhanced release of phytosiderophores under Zn‐deficiency stress may be causally involved in Zn efficiency in genotypes of graminaceous species.
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