Roles of endogenous and exogenous growth regulators in dormancy of Utricularia vulgaris

Abstract

The roles of endogenous and exogenous growth regulators on dormancy control of Utricularia vulgaris were investigated by extraction and bioassay of endogenous levels of four classes at various developmental stages and by measuring the effects of synthetic regulators on these stages. The bioassays used were oat coleoptile for auxins, abscisic acid and other inhibitors; lettuce hypocotyl for gibberellins; and soybean callus for cytokinins. Two weeks before turion formation and during innate dormancy abscisic acidlike and bound gibberellinlike levels were high while free gibberellinlike and auxinlike levels were low. Abscisic acid exogenously applied to actively growing plants rapidly induced turion formation even under noninductive environmental conditions. Kinetin rapidly and completely caused sprouting in innately dormant turions but would not promote continued vegetative growth. These plants formed new turions within 2 weeks of sprouting. During imposed dormancy, when turions rapidly sprouted, there was a low level of abscisic acidlike inhibitor and high levels of gibberellinlike and auxinlike compounds. Turions collected during this state could be maintained in a dormant condition by incubation with abscisic acid even at high temperatures which normally induce sprouting. During sprouting the endogenous growth regulator pattern was similar to that described for imposed dormancy. A model of the environmental and growth regulator factors which control dormancy is presented.