Nectaries and male-biased nectar production in protandrous flowers of a perennial umbellifer Angelica sylvestris L. (Apiaceae)

Abstract

Nectar is the most common floral pollinator reward. In dichogamous species, floral nectar production rates can differ between sexual phases. We studied the structure of nectaries located on the stylopodium and nectar production in protandrous umbellifer Angelica sylvestris. Our study species produced nectar in both floral sexual phases. Nectar sugar concentration was low (on average 22 ± 11 %, mean ± SD) and the nectar hexose rich and composed of sucrose, glucose, fructose and a small amount of amino acids, including b-alanine, a non-protein amino acid. Although nectar composition and sugar concentration varied little between floral sexual phases, nectar production showed a threefold reduction during the stigma receptive period. This is in contrast to other studies of Apiaceae that have reported female-biased nectar production, but in the direction predicted by plant sexual selection theory, suggesting that in pollen-unlimited species, floral rewards mainly enhance male reproductive success. The structure of the nectary was similar at the two sexual stages investigated, and composed of a secretory epidermis and several layers of nectariferous and subsecretory parenchyma. The nectary cells were small, had large nuclei, numerous small vacuoles and dense, intensely staining cytoplasm with abundant endoplasmic reticulum, mitochondria and secretory vesicles. They contained abundant resin-like material that may potentially act as defence against microbes. Starch was rarely observed in the nectary cells, occurring predominantly at the female stage and mainly in guard and parenchyma cells in close proximity to stomata, and in subsecretory parenchyma. The main route of nectar release in A. sylvestris seems to be via modified stomata.

Functional Diversity of Nectary Structure and Nectar Composition in the Genus Fritillaria (Liliaceae)

“…This would be difficult for pollinators to access. Such presentation of nectar may act as a phenotypic filter, preventing insects other than flies, with have a cushion-like labium, to gather floral rewards (Stpiczyńska et al, 2014). …”

Insects associated with sweet fennel: beneficial visitors attracted by a generalist plant

“…Its dichogamous flowers are arranged into large inflorescences-compound umbels of different orders. Like many other umbellifers (Stpiczyńska et al 2015), within individual flower fennel demonstrates functional protandry. At first, flowers pass through a male functional stage with active anthers and then through the female functional stage with active stigma.…”

“…It has been previously found that in dichogamous species nectar production if often different between sexual stages. For example, in Angelica sylvestris it was three times lower during the stigma receptive period (Stpiczyńska et al 2015). Therefore, it is more likely that due to functional protandry and different floral nectar production between sexual phases, not all insects visit both types of flowering umbels.…”

Melliferous Potential of Weedy Herbaceous Plants in Crop Fields of Romania from 1949 to 2012

“…Some taxa have been investigated for secretion biology, e.g. Angelica sylvestris, for which the floral nectar production rates can differ between sexual phases (Stpiczyńska, Nepi, & Zych, 2015). Therefore, the lack of studies on the melliferous potential of other species in the Apiaceae is probably linked with their uniformity in their floral appearance, and their 'weak' melliferous potential probably hides a very large variability (10 to 500 kg/ha).…”