Pseudopollen: Its Structure and Development in Maxillaria(Orchidaceae)

Histochemical analyses of the pseudopollen of ten species ofMaxillaria sectionGrandiflorae revealed that the main storageproduct is protein, although starch is usually also present.Lipids are rare in pseudopollen and thus do not seem to playan important role in attracting insects. In Maxillaria sanderiana,pseudopollen is formed by the fragmentation of multicellular,uniseriate trichomes, derived by the repeated division of asingle, papilla-like, basal secretory cell that contains well-developeddictyosomes, endoplasmic reticulum and mitochondria. At first,there is continuity of cytoplasm between adjacent componentcells of a trichome via plasmodesmata. During maturation, thecytoplasm retracts as the cell volume increases and the plasmodesmatabecome less obvious. Each component cell of the trichome eventuallycomprises a large protein body and a small amount of peripheralcytoplasm containing amyloplasts, a few small lipid bodies,mitochondria and a nucleus with nucleolus. Finally, the trichomeundergoes fragmentation, forming individual cells or chainsof cells of varying lengths. Light microscopy observations indicatea similar sequence in the other species examined. The occurrenceof pseudopollen in section Grandiflorae and alliance Splendensmay indicate that this character has evolved at least twicein Maxillaria. Copyright 2000 Annals of Botany Company Bees, farina, histochemistry, labellum, low-vacuum scanning electron microscopy, Maxillaria, Orchidaceae, pseudopollen, transmission electron microscopy, trichomes