Mechanism of the growth-promoting action of fusicoccin

Abstract

Analogies and differences between the growth-promoting action of fusicoccin (FC), the toxic agent produced by Fusicoccum amygdali, and of indole-3-acetic acid (IAA) in etiolated pea internode segments were further investigated. It was confirmed that the effect of FC, at optimal concentration, on growth by cell enlargement is markedly higher (ca. 70%) than that of IAA. The lack of an inhibitory effect of FC at high concentrations corresponds to a lack of capacity of the toxin to induce ethylene synthesis. When FC and IAA are present together at suboptimal concentrations, the effects of the two substances are clearly additive. Growth stimulation by a mixture of FC and IAA at optimal concentrations is equal to that by FC alone. NaF, 2,4-DNP, actinomycin D, and cycloheximide strongly depress FC-induced stimulation of cell enlargement. These data are in agreement with the hypothesis that FC promotes growth through some effect on cell-wall extensibility probably identical to the one mediating auxin-induced growth, while the primary site of action of FC is different from that of the natural and synthetic auxins.

Review lecture - Hormones in healthy and diseased plants

“…But the hormone-like properties of fusicoccin do not stop there. It will induce extension of etiolated pea internode segments and, as in the case of similar activity by IAA, the extension is accompanied by marked proton extrusion (Lado et al 1972(Lado et al , 1973Marre et al 1974). Even more surprising, while IAA usually inhibits root growth, fusicoccin promotes root extension of many species, and even high concentrations are not inhibitory (Pilet 1976).…”