Comparative studies on structure of the floral nectaries and the abundance of nectar production of Prunus laurocerasus L.

Abstract

There is very scanty information concerning the floral nectary structure and nectar secretion in Prunus laurocerasus L. Therefore, the aim of the study was to determine the micromorphology, anatomy and ultrastructure of nectaries; the abundance of nectar production; and the quantitative and qualitative composition of sugars contained in the nectar of two P. laurocerasus cultivars: ‘Schipkaensis’ and ‘Zabeliana’. The nectary structure was studied using light, fluorescence, scanning and transmission electron microscopy techniques. The nectar sugars were analysed with HPLC. The ‘Schipkaensis’ had longer inflorescences with a larger number of flowers and a longer perianth than ‘Zabeliana’. The micromorphological structure of the nectaries in ‘Schipkaensis’ exhibited denser (approx. 39%) and larger (approx. 50%) stomata and thicker (approx. 13%) cuticular striae forming wider bands (approx. 26%) than in ‘Zabeliana’. The results provide new data on the micromorphology, anatomy and ultrastructure of these floral nectaries. Nectary cuticle ornamentation as well as the size, type and density of stomata and stomatal complex topography can have a diagnostic value in Prunus. The nectar sugar weight indicates a significant apicultural value of the cherry laurel, especially in the case of ‘Schipkaensis’. Cherry laurel is an entomophilous species recommended for cultivation in nectariferous zones and insect pollinator refuges; however, climatic conditions eliminating the invasiveness of these plants should be considered.

Nectar Secretion, Morphology, Anatomy and Ultrastructure of Floral Nectary in Selected Rubus idaeus L. Varieties

“…The present observations showed cuticular striation on the surface of nectary epidermis cells in the six R. idaeus cultivars. Such ornamentation was also reported in other members of the Rosaceae family, e.g., various species of the genera Cotoneaster, Crataegus, Malus, Prunus, Sorbus, and Chaenomeles [20,[45][46][47][48]. Literature data indicate that cuticular ornamentation is a characteristic trait of various cultivars or a group of cultivars [49].…”

“…The ability of the cuticle to repel water molecules is associated with the presence of polymerized fatty acids, which facilitate the flowing drops of the liquid to clean the surface of this layer [51][52][53]. Concurrently, cuticular striae protect nectar against drying and, through limitation of evaporation, extend the duration of nectar exposure to insects, thus substantially enhancing the flower pollination efficiency [20,27,50,54]. As demonstrated by Koteyeva [55], the cuticle layer in specialized secretory tissues, mainly in nectaries, is characterized by a high degree of diffusion-based penetration.…”

“…In comparison with the value of the parameter in Cucurbita pepo [61,62], the number of stomata per 1 mm 2 of the nectary epidermis was similar or comparable in the former cultivar group and clearly lower in the latter group. Chwil et al [20] reported the presence of 45 and 71 stomata in the epidermis of Prunus laurocerasus 'Schipkaensis' and 'Zabeliana', respectively. Nectar precursors generated through metabolic processes overcome various barriers, e.g., the cell membrane, cell wall, and hydrophobic cuticle.…”

“…Nectaries in the Rosaceae family represent the receptacular type. They are composed of three layers: nectary epidermis, nectary parenchyma, and subnectary parenchyma [20,21]. The structure of floral nectaries in the Rubus genus has not been studied.…”

The Role of Cutinsomes in Plant Cuticle Formation

“…These nanoparticles seem to fuse to form the cuticle layer, as in tomato fruit epidermis (compare Figure 2 D, Figure 4 and the scheme in Domίnguez et al [ 66 ]). It is also worth noting that recent TEM studies of nectaries in Epidendrum [ 89 ], Geranium [ 90 ] and Prunus laurocerasus [ 91 ] flowers may point to the presence of cutinsomes, judging from the dark spherical structures located in the epidermal cell wall near the cuticle. Moreover, cutinsome-like structures were observed in the cell walls of the outermost endosperm layer of Olea europea 22 and 26 weeks after flowering [ 92 ].…”