Chemical, morphological, and genetic characterization of the floral scent and scent-releasing structures of Gynandropsis gynandra (Cleomaceae, Brassicales).

Abstract

Flowering plants showcase a remarkable diversity in floral fragrances, colours, and structures, which function harmoniously as signals to attract and guide pollinators. Like visual signals, the scents emitted by flowers can be associated with the attraction of specific pollinator classes. As such, divergence in floral scent composition can be a key isolation mechanism for speciation. Between continents, the leafy vegetable Gynandropsis gynandra possesses differences in morphology, phenology, foliar chemodiversity, and pollinators. Importantly, G. gynandra is pollinated by hawkmoths in Africa, and bees and butterflies in Asia. Here, we combined chemical, morphological, and transcriptome analyses to assess differences in the floral scent and scent-releasing structures between African and Asian G. gynandra accessions, and within flowers of the same accession. The prevalence of nitriles and benzenoids in the floral fragrance of the African and Asian accessions, respectively, corresponds to features typically associated with their differing pollinator classes. Further, we uncovered differences in floral epidermal cell morphology, with papillae present on the petal claws and nectary of the African accession and absent (or reduced) for the Asian accession. Through transcriptomic analyses, we showed that the stalk-like floral structures are putatively involved in terpenoid biosynthesis and emission. However, the epidermal cell morphology and staining suggests that the petals, stamens, and stigma may be involved in scent production of other floral volatile classes (e.g., nitrogen-containing compounds). These additional phytochemical and morphological distinctions between African and Asian accessions suggest that the divergent forms of G. gynandra may merit taxonomic recognition at subspecies level.