
doi: 10.1139/b2012-101
handle: 11365/30974 , 11336/272608
The floral nectaries of Helleborus foetidus L. were studied using scanning and transmission electron microscopy, as well as light microscopy. Nectaries are tubular and consist of an external epidermis, a photosynthesizing parenchyma, large branches of vascular tissue, a nectar-producing parenchyma, and an internal epidermis. The external epidermis is characterized by thick outer walls and a thin cuticle. Cells of the photosynthesizing parenchyma are characterized by chloroamyloplasts. The nectar-producing parenchyma consists of small cells with lobed nucleus, several small vacuoles, and numerous undifferentiated elongated plastids. These cells contain lipid bodies, Golgi membranes, and rough endoplasmic reticulum and are connected by numerous plasmodesmata. Parenchyma cells around sieve elements contain some amyloplasts. The outer cell wall of the internal epidermis displays a central thinned area containing a depression. The cuticle is very thick with amorphous structure, especially evident in its proximal part. Secretion takes place only in the inner basal region of the nectary cup. The surface of the internal epidermis is devoid of secreting structures. Nectar is released by fracture of the cuticle and underlying cell wall; however, epidermal cell death is not apoptotic. This holocrine secretion is coupled with a more common merocrine secretion through which nectar accumulates in subcuticular spaces. This combined secretion mode produces an enriched “nectar soup” crucial for interactions with pollinators and yeasts during winter flowering.
580, 570, Nectar secretion, Holocrine secretion, Helleborus foetidu, nectar production, Nectary structure, Helleborus foetidus; nectar production, https://purl.org/becyt/ford/1.6, Helleborus foetidus, https://purl.org/becyt/ford/1
580, 570, Nectar secretion, Holocrine secretion, Helleborus foetidu, nectar production, Nectary structure, Helleborus foetidus; nectar production, https://purl.org/becyt/ford/1.6, Helleborus foetidus, https://purl.org/becyt/ford/1
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