Journal of Chemical Ecology, Vol. 25, No. 10, 1999 A ROCK-IRON-SOLUBILIZING COMPOUND FROM ROOT EXUDATES OF Tephrosia purpurea K. K. AGGARWAL, 1 J. RAJIV, 2 and C. R. BABU 2, * 1 Centre for Environmental Management of Degraded Ecosystems University of Delhi South Campus Delhi-110 021, India 2 Department of Botany University of Delhi Delhi-110 007, India (Received November 5, 1998; accepted May 30, 1999) Abstract—Root exudates from Tephrosia plants contained a rock-iron [Fe(OH) 3 ] -solubilizing compound. This was purified to apparent homogeneity and appears to possess an iron-binding phenolic moiety linked to a proteinaceous component that may act as a receptor. The lyophilized purified fraction showed maximum Fe(OH) 3 -solubilizing activity at 50°C under acidic pH. Its activity was influenced by trace ions (Co, Cu, Zn, B, Mo, Mn) and toxic metal ions (Ni, Al, Pb, Cr, Hg), but ions such as Na, K, Mg, and Ca had no significant effects on its Fe(OH) 3 -solubilizing activity. Key Words—Tephrosia purpurea, root exudates, Fe(OH) 3 -solubilizing compound, phytosiderophore, bioremediator. INTRODUCTION Iron is a trace element essential for the growth of almost all forms of life; how- ever, its availability is limited to aerobic organisms because of its tendency to form insoluble complexes at biological pH (Ochsner et al., 1995; Powell et al., 1980). A number of adaptive strategies have been evolved by biota to overcome iron-deficiency stress. Production of siderophores under iron stress conditions by microorganisms is well documented (Geurinot, 1994; Briat, 1992; Crichton and Charleteaux-Wauters, 1987; Neilands and Leong, 1986; Neilands, 1981). Plants have been categorized as having strategy I and strategy II responses based upon their adaptations to iron-deficiency stress (Jolley et al., 1996; Hop- kins et al., 1992a; Romheld and Marschner, 1986). Dicotyledenous and nongram- *To whom correspondence should be addressed. 2327 0098-0331/99/1000-2327/$16.00/0 © 1999 Plenum Publishing Corporation