Nectary ultrastructure of Cabomba caroliniana Gray (Cabombaceae)

Abstract

Cabomba Aubl. is a genus considered as a potential genetic model for studies of early angiosperm evolution, accordingly, it is important to expand the knowledge of it. This paper reports the study of the anatomy and the ultrastructure of the nectary of Cabomba caroliniana Gray using bright-field microscope, scanning and transmission electron microscope in order to understand its secretion mechanism. C. caroliniana has protoginous flowers and the anthesis lasts two days. Nectaries of C. caroliniana are located in two basal lobes or yellow auricles of each white petal. Most nectar is observed in the area above the pronounced auricles. The secretion is released mainly by the four-cellular trichomes or hydropotens present in both nectary epidermis. The cellular ultrastructure indicates that the nectary is active during the two days of the anthesis. This agrees with the fact that in both anthesis days the fertile structures of the flower (first the stigmata and then the anthers) are disposed above the nectaries. The nectar secretion mechanism is discussed in relation to the present knowledge. The results of this study are related to what has been described for other basal angiosperms.