By using two tomato genotypes line 227/1 (Fe chlorosis susceptible) and Roza (Fe chlorosis tolerant) and their reciprocal F(1)hybrid, some root morphological changes, pH changes of nutrient solution, reduction capacity of Fe-III and uptake and root-to-shoot translocation of Fe-59 were studied under controlled environmental conditions in nutrient solution with 3 different Fe supplies as Fe EDDHA (i.e., 10(-7) M, severe Fe deficiency; 10(-6) M, intermediate Fe deficiency; 10(-4) M, adequate Fe supply). Tolerant parent `Roza' was less affected by low Fe supply than susceptible parent `line 227/1' as judged from the severity of leaf chlorosis. Under both Fe deficient conditions there were no differences between the reciprocal hybrids concerning the appearance of chlorosis. Under intermediate Fe deficiency, reciprocal F-1 hybrids (`line 227/1 x Roza' and `Roza x line' 227/1) showed an intermediate chlorosis between tolerant and susceptible parents. However, under severe Fe deficiency the reciprocal hybrids were more chlorotic than the tolerant parent irrespective of which parent was the cytoplasm contributor. A decreased Fe supply during preculture enhanced (FeII)-I-I reduction capacities of the parents and reciprocal hybrids. Differences in the tolerance to Fe deficiency always were better correlated with (FeII)-I-I reduction capacity of the genotypes than the Fe deficiency-induced release of H+ ions. Under both Fe deficient conditions the tolerant parent Roza had a much higher (FeII)-I-I reduction capacity than the susceptible parent line 227/1. The reduction capacity of the hybrids `Roza x line 227/1' was very similar to the capacity of the parent Roza, but higher than the capacity of the hybrids `line 227/1xRoza' at both Fe-deficient conditions. Under both Fe deficient conditions tolerant parent had higher number of lateral roots than the susceptible parent. Among the reciprocal hybrids `Roza x line 227/1' possessed more lateral roots than the `line 227/1 x Roza' under both Fe deficient conditions. Low Fe nutritional status resulted in marked increase in root uptake of (5)9Fe. At adequate Fe supply, reciprocal hybrids and their parents did not differ in uptake and root-to-shoot translocation of Fe. However, under Fe-deficient conditions uptake and root-to-shoot translocation of (5)9Fe were significantly higher in the Fe chlorosis tolerant than the susceptible parent. Based on the reduction capacity of (FeII)-I-I and uptake and root-to-shoot translocation of Fe, the F-1 hybrids obtained from the cross in which the maternal genotype was Roza appeared to be more tolerant than when the maternal genotype was the susceptible line 227/1. Uptake and translocation ratio of the F-1 hybrids obtained from `Roza x line 227/1' were similar to those of the parent Roza, but higher than the F-1 hybrids obtained from `line 227/1 x Roza', particularly under intermediate Fe deficiency. The results indicate that (FeII)-I-I reduction show a better relationship to Fe efficiency than Fe deficiency induced release of H+ ions. The inheritance of Fe deficiency tolerance of Roza seems not to be simple monogenic. It might be characterised by both, nuclear and extranuclear heredity. The intermediate responses of the reciprocal hybrids of the `line 227/1 x Roza' indicates that the Fe deficiency tolerance character of Roza is transferable by nuclear heredity. The better responses of the hybrids of `Roza x line 227/1' than the hybrids of `line 227/1 x Ro