Tentoxin sensitivity of citrus: cotyledon-dependency of growth inhibition and reversibility of chlorosis

Tentoxin is a cyclic tetrapeptide, produced by the fungus Alternaria alternata, that induces chlorosis in germinating seedlings of some angiosperms. Since the most pronounced chlorotic effect of tentoxin is at the initial stages of germination most studies have evaluated the effects of tentoxin on cotyledons. In this preliminary work a unique biological system was established for the study of the mechanism of tentoxin-induced chlorosis in developing citrus seedlings. This system was used to compare the effects of tentoxin on the in vitro germination of intact versus decotyledonized embryos. It is demonstrated here that the chlorotic effect of tentoxin is reversible and that tentoxin blocks the ability of decotyledonized embryos to utilize nutrients from the growth medium and, therefore, to compensate for the lack of cotyledons. The citrus system offers a unique way to study the relation between the effect of tentoxin on the activity of choloplast ATPase and the induction of chlorosis.