When challenged with Fe deficiency, plants, especially dicots, release phenolic molecules that influence Fe and P mobility (Röm- held, 1987). An example is the release by Fe-deficient alfalfa plants of the isoflavonoid phytoalexin [2-(3′,5′- dihydroxyphenyl)-5,6-dihydroxyben zofuran], which intensely dissolves ferric phosphate, thus making Fe and P available for plant utilization, and also serves as phytoalexin against infecting pathogens (Masaoka et al., 1993). Interestingly, Fe-sufficient plants produced root exudates that were limited in ferric phosphate- dissolving capacity. Fe-deficient tomato plants also exude caffeic acid for solubilizing Fe from insoluble Fe sources (Olsen et al., 1981). These phenolics make Fe and P available by forming relatively stable che- lates with Fe and Al present in insoluble Fe- and Al-phosphates thereby increasing the solubility of Fe and P for plant uptake (Figure 1).