The physiology of dormancy in potato tubers and its relations with the hormonal mechanism of tuberization

Abstract

Dormancy * is a particular physiological state in which the buds of potato tubers does not germinate owing to internal factors even though they are placed under optimal environmental conditions. The length of the dormant period is relatively insensible to environmental factors, but it is correlated with high levels of the f inhibitor-complex and with a very low activity of endogenous gibberellins and cytokinins in the periderm and the buds. On the contrary, the end of his period coinciles with a sharp decrease of the inhibitor and dith at drastic increase in the levels of those phytohormones. The mechanism through which the inhibitor-complex (whose principal component is abscissic acid (ABA) ) controls dormancy is not well established. Recent evidence shows that ABA inhibits DNA and RNA synthesis of a -amylase and other hydrolitic enzymes. It also acts as an cncouplant factor for oxidative phosphorilation. Nevertheless, is has been also put in evidence that any of the inhibitors (/3 -complex or ABA) stimulate tuberization in sprout sections in vitro cultured. Moreover, under favorable photoperiodic conditions (short-days) or unfavorable ones (long-days or continuous light) for tuberization, the foliage synthesises similar high levels of the inhibitor-complex which seems to be translocated to the periderm of growing young tubers where it gradually accumulates. When the concentration of the inhibitor rises above a certain level, the tubers are dormants. It has been also demonstrated the in vitro set of non-dormant tubers when the nutrient medium contains quercetine. These facts suggest a certain independence between the mechanisms of tuberization and tuber dormancy.