The floral nectaries of Helleborus foetidus 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 thin cuticle. Cells of the photosynthesizing parenchyma are characterised by the presence of 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 the sieve elements contain some amyloplasts. The outer cell wall of the internal epidermis displays a small thinned area with a pinch inside. The cuticle is very thick, and consists of a globular structure evident especially 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. The fracture point of the cuticle and underlying cell wall is the mechanism of nectar release, nonetheless epidermal cell death is not apoptotic. This holocrine secretion is coupled with a more common merocrine secretion through which nectar accumulates in the subcuticular spaces. The consequence of the combined manner of secretion is an enriched “nectar soup” crucial in the interaction with pollinators and yeasts during winter flowering.

Vesprini, J., Pacini, E., Nepi, M. (2012). Floral nectar production in Helleborus foetidus L.: an ultrastructural study. BOTANY, 90, 1308-1315.

Floral nectar production in Helleborus foetidus L.: an ultrastructural study

PACINI, ETTORE;NEPI, MASSIMO
2012-01-01

Abstract

The floral nectaries of Helleborus foetidus 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 thin cuticle. Cells of the photosynthesizing parenchyma are characterised by the presence of 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 the sieve elements contain some amyloplasts. The outer cell wall of the internal epidermis displays a small thinned area with a pinch inside. The cuticle is very thick, and consists of a globular structure evident especially 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. The fracture point of the cuticle and underlying cell wall is the mechanism of nectar release, nonetheless epidermal cell death is not apoptotic. This holocrine secretion is coupled with a more common merocrine secretion through which nectar accumulates in the subcuticular spaces. The consequence of the combined manner of secretion is an enriched “nectar soup” crucial in the interaction with pollinators and yeasts during winter flowering.
2012
Vesprini, J., Pacini, E., Nepi, M. (2012). Floral nectar production in Helleborus foetidus L.: an ultrastructural study. BOTANY, 90, 1308-1315.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11365/30974
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