THE ROLE OF THE LENS IN CONTROLLING HEAT-INDUCED BREAKDOWN OF TESTA-IMPOSED DORMANCY IN NATIVE-AUSTRALIAN LEGUMES

A high proportion of seeds of most species of the Fabaceae have testa- imposed dormancy, which prevents them from imbibing water even under f avourable environmental conditions. This allows seeds to accumulate in a persistent soil seed bank. Dormancy is usually considered to be bro ken only when the testa is disrupted, particularly at the lens. In Med iterranean-type ecosystems, the primary natural mechanism causing the breakdown of this dormancy is the disruption of testas in the soil see d bank by heat from fires that warms the soil in which the seed bank o ccurs. We examined experimentally the role of the lens in controlling this heat-induced breakdown of dormancy in 16 native Australian specie s of the Faboideae and Mimosoideae. Two groups of patterns are recogni zed: species of the Mimosoideae: Acacieae and Faboideae: Mirbelieae, w here water permeability is regulated by the lens; and species of the F aboideae: Bossiaeeae, where water permeability apparently occurs at no n-localized regions of the tc:sta. The species in these two groups dif fer in the structure of their testas. Thus, testa-imposed dormancy doe s not represent a single dormancy mechanism in legumes, as is often as sumed when dormancy is broken artificially. (C) 1998 Annals of Botany Company.