Abstract
The genus Zeyheria (Bignoniaceae) comprises only two species, both of which have been described as possessing a reduced and non-functional nectary disk. Despite the importance of this evolutionary change in the floral nectary, these functional assumptions have been based on disk size and on the distribution, abundance and histochemistry of corolla-borne trichomes. By combining methods on light and electron microscopy, here we investigated the functionality of the reduced nectary disk and describe all of the tissues and structures of the nectar chamber in order to determine the sites of floral nectar secretion in both Zeyheria species. . Our data find the floral nectary traits of both species to be very similar, although differing in their cellular contents. Subcellular evidence in both species indicated that disk, stipe and petal axils were, predominantly, involved in hydrophilic secretion, while capitate glandular trichomes produced lipophilic secretion and papillae produced mixed secretion. Our study shows that in spite of its reduced size, the reduced disk functions in nectar secretion in both species of Zeyheria. This kind of nectary system is a novelty for Bignoniaceae, since it comprises several tissues and structures functioning in an integrated fashion.
Highlights
Nectar is an aqueous solution produced by specialized structures, largely distributed among angiosperms (Fahn 1979; Smets 1986; Nepi et al 2009)
By combining methods on light and electron microscopy, here we investigated the functionality of the reduced nectary disk and describe all of the tissues and structures of the nectar chamber in order to determine the sites of floral nectar secretion in both Zeyheria species
The similar results are presented for the two studied Zeyheria species and the differences between them were highlighted in the text
Summary
Nectar is an aqueous solution produced by specialized structures (nectaries), largely distributed among angiosperms (Fahn 1979; Smets 1986; Nepi et al 2009). Bignoniaceae species are predominantly zoophilous (Gentry 1974; Alcantara & Lohmann 2010) and the floral nectar production has been commonly attributed to a conspicuous nectary, characterized as a disk that surrounds the ovary base (Gentry 1992; Galetto 1995; 2009; Rivera 2000). This nectariferous disk is usually composed by a secretory epidermis and secretory parenchyma, predominantly supplied by phloem (Galetto 1995; Thomas & Dave 1992; Rivera 2000; Guimarães et al 2016). Ultrastructural and chemical analyses are essential to investigate relationships between structure and cell functions (Fakan 2004)
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