Accumulation and within-seed distribution of iron in common bean and soybean

The influence of times of applying FeEDDHA on seed yield and Fe accumulation by four common bean (Phaseolus vulgaris L.) and two soybean (Glycine max L.) genotypes grown on a calcareous soil was studied under greenhouse conditions. The soybean genotypes, unlike the common bean genotypes, developed Fe-deficiency chlorosis and responded to application of the chelate. A preplant application of FeEDDHA was more efficacious than a flowering application in increasing seed yield of soybean. In contrast, the flowering application was much more effective than the preplant application for increasing seed Fe concentration [Fe] of both species. Percentage of seed Fe located in the seed coat of the common bean genotypes ranged from approximately 5 to 40% and was little affected by FeEDDHA. This within-seed distribution of Fe was correlated with methanol-extractable seed-coat pigments absorbing at 500 nm, presumably anthocyanins, but not with condensed tannins (proanthocyanidins). The soybean genotypes did not accumulate anthocyanins or tannins in the seed coat. Seed of Fe-deficient soybean plants without FeEDDHA had appreciably lower [Fe] and had a lower percentage of seed Fe in the seed coat than treated plants. Within-seed distribution of Fe should be considered in plant breeding because of concerns about both human nutrition and early seedling growth.