Morphology, structure and ultrastructure of staminal nectary in Lamprocapnos (Fumarioideae, Papaveraceae)

Nectaries show high a degree of variations in terms of location, morphology and structure; these characteristics are critical for systematic information. In Papaveraceae, staminal nectaries at the stamen base are only found in bisymmetric and zygomorphic flowers, but with little description on the ultra-structure of nectary available. Here we investigate structural details of flowers and nectaries of Lamprocapnos spectabilis using LM, SEM and TEM. The nectaries of L. spectabilis are initiated at the base of stamen filaments in the young bud. The oval/ball-shaped staminal nectaries are composed of four major types of tissues in general. First and outmost layers are epidermis and hypodermis with large and elliptical cells. Beneath the epidermal layers are the second type of tissue consisting of 20-30 layers of parenchyma cells which are further distinguished by two kinds of cells: smaller secretory parenchyma cells having dense cytoplasm, large nucleus and abundant cellular organelles, and larger sub-nectary parenchyma cells containing a relatively thin cytoplasm. The third type of tissue is the darkly-stained elongated cells and embedded at 8- to 12-cell-layer deep in the nectaries, and is associated with sieve tube elements and cells resembling companion cells, and they presumably belong to underdeveloped sieve tube elements or “protophloem” based on ultrastructure features such as conspicuous cell wall ingrowths and plentiful plasmodesmata. The forth type of tissue in the nectary is the simplified vascular bundle forming with only phloem. It is reasonable to suggest that secretions in the spacious intercellular spaces between secretory parenchyma cells are exuded to the exterior via micro-channel or epidermis/cuticle pathway. In conclusion, the results show that epidermis, hypodermis, secretory parenchyma, “Arber suggestive tissue (protophloem)”, and phloem act coordinately in nectar production, secretion and exudation in Lamprocapnos. The structure of the staminal nectaries are compared within Papaveraceae and with other related groups in Ranunculales.