Presence of the anther gland is a key feature in pollination of the early‐branching papilionoidsDipteryx alataandPterodon pubescens(Leguminosae)

Abstract

The presence of glandular appendages in the anthers is a rare condition in angiosperms. In Leguminosae it occurs in species of the Mimosoid clade and in earlybranching clades of papilionoids such as Dipterygeae. In Dipterygeae such appendages surprisingly exhibit a secretory cavity instead of secretory emergences as is the case for the Mimosoid clade. Thus, the objective of this study was to elucidate the function of anther glands in Dipteryx alata and Pterodon pubescens, species in the Dipterygeae clade that exhibit a pollen release mechanism that is intermediate between the explosive and valvular types.• Flower buds and flowers were processed for surface, anatomical, histochemical and ultrastructural analyses.• Anther glands consist of a cavity secreting sticky substances (oleoresins and polysaccharides) that play a key role during the flower's lifespan by aggregating pollen grains and attaching them to the floral visitor's body. Other floral features that are important for understanding the pollen release mechanism that is intermediate between the valvular and the explosive types are: (i) keel petals intertwined with tector trichomes; (ii) glandular appendages in the abaxial and lateral sepals and in petals composed of secretory ducts; and (iii) a continuous secretion process of the anther glands followed by an asynchronous dehiscence of anthers.• The well-adapted papilionoid flag blossom with anther glands and keel petals intertwined with trichomes provided the foundation for a successful canalisation toward a pollen release mechanism intermediate between the explosive and valvular types inside early-branching papilionoids.

Structural and histochemical attributes of secretory ducts and cavities in leaves of four species of Calophyllaceae J. Agardh in Amazonian savannas

“…Previous studies have reported that the epithelium and parenchymatous sheath act as secretion production sites (Rodrigues et al, 2011a,b;Leite et al, 2014;Palermo et al, 2018). The ultrastructure of epithelial cells shows that the secretion is externalized to the lumen by the eccrine mechanism, corroborating the study of Leite et al (2019). The presence of numerous vesicles showing the path of cell secretion towards the lumen, fusion of vesicles and the accumulation of secretions in the periplasmic space of epithelial cells is a strong indication of a granulocrine secretory process (Franco & Albiero 2018;Almeida & Paiva 2019).…”

“…Epithelial cells with thin, disorganized walls, a winding plasma membrane, vacuolization, low-density peripheral cytoplasm with little osmiophilic material, few organelles and mitochondria and numerous vesicles adhered to the membrane are evidence that secretory cells do not present an intense secretory process, as observed in duct and cavity-secreting epithelial cells in the literature (Franco & Albiero 2018;Palermo et al, 2018;Leite et al, 2019;Haratym et al, 2020). However, our results corroborate Peng et al (2012) and Turner & Lange (2015) when describing ultrastructural characteristics of cavities in adult tissue, and in part with results of Lacchia & Carmello-Guerreiro (2009) for epithelial cells of secretory ducts of Anacardiaceae in the senescent stage.…”

“…The presence of few mitochondria is another indication that the ducts were in the post-secretory stage, since it is common to find many mitochondria in secretory cells with intense cellular activity (Franco & Albiero 2018;Leite et al, 2019). Oil droplets in the cytoplasm of epithelial cells close to the plasma membrane indicate fusion of these droplets with the membrane, and subsequently, externalization of their content to the lumen of the duct, similar to processes in resiniferous secretory cavities (Paiva & Machado 2006).…”

“…This being a great advance in understanding how the production of protective metabolites occurs. Phenolic compounds, lipids, essential oils, oleoresins, mucilage, neutral polysaccharides, proteins and alkaloids are metabolites related to plant defence against herbivores and/or pathogens (Fahn 1979;Langenheim 2003;Mumm & Hilker 2006;Leite et al, 2019).…”

Comparative Floral and Pollen Micromorphology of Leonurus japonicus and L. macranthus (Lamiaceae)

“…Gland-secreted secondary metabolic compounds such as aromatic compounds, essential oils or floral volatile scents act directly on the attraction of pollinators or defense against herbivory [9][10][11][12][13]. Several functions of anther glands have also been reported, such as containing adherent substances to aggregate pollen grains and attach them to the pollinator body [14][15][16][17][18], being rewarded as food to the pollinator, and containing substances for defense against phytophagous insects [15]. Moreover, floral stomata may act in the exudation of nectar [19,20] or emission of volatile organic compounds [21,22].…”