Mechanisms for the coupling of iron and glyphosate uptake in Catharanthus roseus cells

In Catharanthus roseus cells, recent data have indicated that glyphosate is taken up in cell suspensions by an Fe/glyphosate cotransport, stimulated b y the action of Ca2+. In this work, experiments were designed to determine the nature of the coupling mechanisms involved. Two biochemical mechanisms were shown to interplay in the cellular absorption of Fe2+, the transported form of iron: a fast diffusional process after the transfer of cells into the medium and a slow component mediated by an Fe transporter and stimulate d by the action of Ca2+. There was evidence to suggest that glyphosate abso rption is associated with the slow component of Ca-dependent iron uptake: ( i) glyphosate and iron uptakes exhibit the same kinetics with respect to me dium FeSO4 concentrations, with the presence of a saturable phase and the e xistence of a similar K-m for Fe and glyphosate absorption; (ii) in presenc e of the ferrous form of Fe in the medium, glyphosate uptake is greatly inh ibited by bathophenanthrolinedisulfonic acid (BPDS), which specifically for ms a complex with Fe2+; and (iii) BPDS also inhibits the cellular absorptio n of glyphosate with the ferric form of iron, suggesting that the effective ness of Fe3+ in promoting the transport of glyphosate is due, in part, to i ts ability to be reduced to Fe2+. In support of this observation, cadmium, an inhibitor of the Fe3+ reductase, also inhibited the uptake of the herbic ide in the presence of FeCl3. Ca2+-dependent Fe/glyphosate cotransport, whi ch was demonstrated in C. roseus, was found to occur with different degrees of efficiency in various plant cell suspensions, indicating that this glyp hosate uptake process can be considered to be a general mechanism in plant cells. (C) 2000 Academic Press.