CHARACTERIZATION OF Zn EFFICIENCY IN IRANIAN RICE GENOTYPES II. INTERNAL UTILIZATION EFFICIENCY

Four rice genotypes differing in Zn efficiency were selected to study the physiological mechanisms for different susceptibility of genotypes to Zn deficiency. It was demonstrated that Zn efficiency was not associated with flooding tolerance, so that flooding tolerance trait could be detected among both Zn-efficient and Zn-inefficient genotypes. Total and water soluble Zn concentrations in shoot and roots showed that Zn efficiency was not due to different inactivation of Zn in plant tissues. Zn-efficient genotypes showed a higher re-translocation of Zn from mature to younger just growing leaves, and responsiveness to low Zn supply was observed only in Zn-efficient genotypes. Activities of two important Zn-enzymes, SOD (superoxide dismutase) and ADH (alcohol dehydrogenase), were affected by both Zn nutritional status and flooding. However, changes in the activity of SOD in shoot were not associated with Zn efficiency response, but in roots reduction of SOD activity in Zn-inefficient as well as an increase in Zn-efficient genotypes were observed. Changes in the activity of ADH did not correlate either with Zn deficiency or flooding response of the genotypes studied.