Using two barley (Nordeum vulgare L.) cultivars differing in Zn efficiency (Tarm?92: Zn?efficient; Hamidiye?79: Zn?inefficient), the effect of varied zinc (Zn) and iron (Fe) supply on the rate of phytosiderophore release was studied under controlled environmental conditions in nutrient solution during the 20 days of growth. Visual Zn deficiency symptoms such as inhibition in shoot length and development of necrosis and reddish?brown lesions on leaves, mainly along the leaf edges and tips, were first and more distinctly observed in Hamidiye?79 than in Tarm?92. However, in both cultivars shoot and root growth was similarly affected by Zn deficiency. Under Fe deficiency, Tarm?92 and Hamidiye?79 did not differ in severity and development time of leaf chlorosis as well as decreases in shoot and root growth. In plants supplied adequately with Zn and Fe, the release rate of phytosiderophores was very low and could not exceed 1 μmol 42 plants−1. 3h−1. However, under Zn deficiency and especially Fe deficiency the plants showed marked increases in rate of phytosiderophore release. Under Fe deficiency, Tarm?92 and Hamidiye?79 were more or less similar in their capacity to release phytosiderophores. The maximal rate of phytosiderophore release under Fe deficiency was, on average, 20 μmol per 42 plants and 3h for both cultivars. In the case of Zn deficiency, Zn?efficient Tarm?92 released higher amounts of phytosiderophores than Zn?inefficient Hamidiye?79. The rate of phytosiderophore release under Zn deficiency reached maximal values of 7 μmol for Tarm?92 and 3 umol for Hamidiye?79, expressed per 42 plants and 3h.
The presented results indicate a possible role of phytosiderophores in Zn efficiency in barley. The role of phytosidrophores was discussed in terms of enhancements in solubility and mobility of Zn both in the rhizosphere and within the plants. The results also demonstrate that the release of phytosiderophores from roots of graminaceous species is not solely a specific response to Fe deficiency; It is also an adaptive response occurring under Zn deficiency.