Floral nectary structure and nectar composition in Eccremocarpus scaber (Bignoniaceae), a hummingbird‐pollinated plant of central Chile

Abstract

Surface features, anatomy, and ultrastructure of the floral nectary of Eccremocarpus scaber (Bignoniaceae), pollinated predominantly by the largest‐known hummingbird (Patagona gigas gigas), were studied together with nectar sugar content and secretion rate. The annular disk nectary comprises epidermis, secretory and ground parenchyma with intercellular spaces, and branched vascular bundles terminating in the secretory parenchyma where only phloem is found. Amyloplasts and vacuoles increase in size throughout development, the latter becoming sites of organelle degradation. Transferlike cells in nectary phloem and P‐proteinlike fibrillar material in phloem parenchyma were observed. Flowers produced around 32 μl of nectar (mostly after anthesis) with 11 mg of sugar composed of fructose, glucose, sucrose, and maltose in a ratio of 0.34:0.32:0.17:0.17. Morphological studies as well as the presence of maltose and glucose in nectar suggest storage of the originally phloem‐derived sugars as starch with its subsequent hydrolysis. The low sucrose/hexose ratio (0.25) and high nectary secretion force (nectar per flower biomass) observed places E. scaber close to large‐bodied bat‐pollinated plants. A hypothesis based on nectar origin and nectar secretion is advanced to explain pollinator‐correlated variation in sucrose/hexose ratio.

Flower nectary structure in Cornus alba L.

“…The presence of plastids containing starch grains suggests intensive synthesis of sugars which are accumulated in the cells of the nectariferous layer and then used for nectar production. Such correlations in nectariferous tissue cells are also reported by other authors (Durkee et al 1981;Belmonte et al 1994;Nepi et al 1996;Weryszko-Chmielewska et al 2003;Paiva and Machado 2008). The remaining cells of the dogwood gland, exhibiting symptoms of destruction, were characterized by a structure similar to that observed in cells of the nectaries in other plants after several days from the end of the nectar secretion stage (Zer and Fahn 1992;Nepi et al 1996;O'Brien et al 1996).…”

“…Similar dependences were found (Vezza et al 2006) in nectaries of Hedera helix. In different species of plants, similar change in nectary color (accumulation of not only anthocyanins but also b-carotenes) marks: (1) the duration of the ripening stage of nectary or (2) the end of the nectar secretion period or/and (3) informs pollinators about the unattractiveness of flowers (Belmonte et al 1994;O'Brien et al 1996;Thornburg 2007). Moreover, accumulation of anthocyanin in plant tissues, maybe as a response to low temperature, has been observed in autumn (Leng et al 2000).…”

Transfer cells in trichomatous nectary in Adenocalymma magnificum (Bignoniaceae)

“…Belmonte et al 1994, Rivera 2000, Lopes et al 2002, Nogueira et al 2013. However, in A. magnificum different events occur simultaneously, which were understood by the manner in which a heterogeneous secretion was released in the presence of chemical substances produced by various metabolic pathways, unique to secretory structures.…”

Can red flowers be conspicuous to bees?Bombus dahlbomiiand South American temperate forest flowers as a case in point

“…(Belmonte et al, 1994) and Tristerix verticillatus R. et Pav. (Loranthaceae) (J.M.-H., personal observation).…”