Comparative analysis of the effects of fusicoccin (FC) and of its derivative dideacetylfusicoccin (DAF) on maize leaves and roots

Abstract

In maize (Zea mays L. cv. DEKALB XL 640) leaf discs or root segments fusicoccin (FC) is by about 5‐10 times more active than its derivative dideacetylfusicoccin (DAF) in stimulating proton extrusion and the hyperpolarization of the transmembrane electrical potential (PD). Also the uptake by leaf discs in liquid medium and the affinity for a receptor present in cell free membrane preparations are by 3–5 times greater for FC than for DAF, while a much greater difference (by about two orders) in activity between the two substances is observed for their effects on leaf transpiration.FC reaches in the leaf tissue a concentration much higher than that of DAF. This is interpreted as due to the higher activity of FC in inducing stomata opening, thus accelerating the transpiratory water flow. The long distance translocation of both FC and DAF mainly depends on mass flow. Thus the initial stimulus on transpiration would induces an increase in concentration of the active substance in the reactive tissue, in a kind of autocatalytic cycle, resulting in the amplification of the difference in activity at cell level between the two toxins.The data on the promotion of H+ extrusion and the hyperpolarization of PD confirm the correlation and thus the possible cause‐effect relationship between FC (or its less active derivative DAF) binding to a receptor at the membrane, and the functions studied. The relationships between the “pathological” (transpiration and wilting) and the “physiological” (electrogenic proton secretion) effects of FC and DAF are also in agreement with the view that all of the known effects of FC and of its active derivatives can be explained as consequences of the activation of electrogenic proton extrusion.