Chemical composition and secretion biology of the floral bouquet in legume trees (Fabaceae).

Abstract

In the present investigation, we studied the floral bouquet and its associate osmophores in three legume trees using a combination of chemical and ultrastructural analyses, a poorly investigated approach to plant glands. The purpose was to understand the secretory process of osmophores and to identify which of the substances produced are responsible for the attraction of pollinators. Petals from buds and flowers of Bauhinia rufa, Caesalpinia pulcherrima and Hymenaea courbaril were fixed and processed for analysis by transmission electron microscopy. Fresh petals of H. courbaril and C. pulcherrima were also collected, submitted to a headspace solid-phase micro-extraction method and analysed using GC-MS. Typical subcellular features of terpene-secreting osmophores were detected: abundance of mitochondria with conspicuous cristae, plastids with plastoglobuli, rough endoplasmic reticulum and the presence of vesicles and oil droplets in the cytoplasm. Novel subcellular characters of osmophores were detected, such as cellular vacuolation in stages far preceding anthesis and a wealth of dictyosomes. The ultrastructure confirmed that the osmophores produce terpenes and phenolic compounds as previously reported. However, the GC-MS analyses showed that only the terpenes are released and could act on pollinator attraction. The phenolics accumulated are mobilized from these structures and metabolized/reabsorbed by the other plant tissues.