The influence of a growth stimulating low Cr III concentration (1.0 μM) on chloroplast ultrastructure, the Fe, Cr, and Mn content of chloroplast extracts, o-phenantroline extractable leaf Fe, and catalase activity was studied in both Fe-sufficient and Fe-deficient bush bean (Phaseolus vulgaris L.) plants. Chromium supply hardly affected the chloroplast ultrastructure of Fe-sufficient plants but significantly improved chloroplast ultrastructure in Fe-deficient leaves. Generally, Cr supply did not significantly influence chloroplast Fe-content, but increased the Fe/Mn ratio in Fe-deficient chloroplasts. In leaves from Fe-deficient plants, o-phenantroline extractable Fe was significantly increased, while catalase activity was not significantly influenced by Cr supply. The possible mechanisms of the beneficial effects of Cr III in Fe-deficient plants are discussed. © 1991 by Marcel Dekker, Inc.