Ultrastructural aspects of the hypanthial epithelium of Selenicereus grandiflorus (L.) Britton & Rose (Cactaceae)

Abstract

Summary The epithelium of the basal part of the inside floral tube (hypanthium) of Selenicereus grandiflorus (L.) Britton & Rose was investigated with ultrastructural and cytochemical methods, while a Gas Chromatography/Gas Mass analysis was performed on the secretion products of this flower tissue. Despite its position (frequently occupied by “classical” nectaries in many representatives of Cactaceae) the cells of the investigated epithelium show features that are typical of cells involved prevailingly in lipidic production. Lipids are stored in the big vacuole which fills almost the whole cell in the last developmental stage. The secretion is of holocrine type and probably started by the mechanical action of the pollinator itself. However sugars conveying from the underlying parenchyma towards the epithelium and a strong PAS-positive reaction at the vacuolar level was observed. These observations suggest also an important presence of carbohydrates in the last products. The formation of subcuticular spaces indicates also an eccrine type of secretion. The results obtained with Gas Chromatography/Gas Mass analysis indicate the production of some phenols, that we link to flower scent. This is the first report on oils producing flowers among Cactaceae and the first for nocturnal flowers.