Apical abortion in calabrese is induced by periods of low temperature and results in premature differentiation of apical meristem cells

Abstract

Apical abortion in calabrese (Brassica oleracea var. italica), a highly destructive disorder which occurs in overwintered transplants, has been investigated using a model system in which blindness (abortion of the apical meristem) can be reproducibly and predictably induced. An initial experiment examined the susceptibility of 12 cultivars to apical abortion when grown throughout a winter period under commercial conditions. Three of those varieties showed very high levels of blindness (100%). Subsequently, plants of the susceptible cultivar PETO 7204 were subjected to an inductive period of low light intensity (30 μmol m -2 s -1 ) and low temperature (4°C). Apical meristematic cells of all plants ceased mitotic activity within 3 d of being transferred to a regime comprising higher light intensity (100 μmol m -2 s -1 ) and temperature (15°C). Using this system the structures of normal apices were compared with those which became blind. Blindness was characterized by a cessation of leaf primordium production by the vegetative apex, the last formed primordium growing on in some cases to form a mature normal leaf, or in others, a deformed structure known as a whip-tail. The inactive apical bud became embedded in the tissues of this last-formed structure. The cells of the inactivated apical bud remained alive, but lost their meristematic capability, becoming enlarged, highly vacuolated parenchyma cells with amyloplasts.