Mirosława Chwil
The structure of the floral nectaries and apicultural value of some plant species of the subfamily Prunoideae (Rosaceae) 
zeszyt 375, ss. 108
The aims of this study was to get to know in detail the structure of the floral nectaries of some cultivars of five plant species of the genus Prunus. To this purpose different microscope techniques were used which allowed the micromorphology, anatomy and ultrastructure of the nectary glands to be described. The apicultural to be described value of 2, 3 cultivars from each species was also determined based on total nectar and pollen production by flowers, but also on the basis of the qualitative and quantitative composition of nectar sugars as well as the protein content and the composition of amino acids in pollen grains.
The present study, conducted in the period 2006-2010, covered the following species (5) and cultivars (14): apricot (Prunus armeniaca L.) ‘Harcot’, ‘Early Orange’, ‘Wczesna z Morden’; peach (Prunus persica (L.) Batsh ) ‘Redhaven’, ‘Veecling’; sweet cherry (Prunus avium L.) ‘Kordia’, ‘Regina’, ‘Vega’; sour cherry (Prunus cerasus L.) ‘Łutówka’, ‘Northstar’, ‘Kelleris 16’; and plum (Prunus domestica L.) ‘Bluefre’, ‘Cacanska Najbolja’, ‘Top’. The structure of the nectaries was examined using fluorescence, light, scanning and transmission electron microscopy. The rate of nectar production was investigated by the pipette method. The qualitative and quantitative analysis of nectar sugars was performed using high performance liquid chromatography (HPLC). Total nitrogen content was determined by the Kjeldahl method, while the amino acid composition in pollen was determined by the method of Davis and Thomas [1973]. Pollen production by flowers was investigated using the modified method involving ether extraction and weight measurement [Warakomska 1972].
Secretion of nectar on the surface of the nectary in the studied flowers occurs through actinocytic stomata distributed at a density of 69 to 151 on the surface 1 mm2 of the epidermis. In the ultrastructure of the epidermal cells of the nectary, differences in the height of the projections of the outer cell wall were found. The structure of mitochondria with a well-developed system of membranes and their location in the close vicinity to the Golgi bodies indicate the interaction of these structures and high metabolic activity of glandular tissue. The density of secretory vesicles near the cell wall and their fusion with the plasmalemma as well as the release of their content into the periplasmic space suggest granulocrine secretion and apoplastic transport of nectar. Total nectar production by flowers of the studied cultivars was 3.2–11.43 mg. The investigated cultivars are arranged as follows in the increasing order of the weight of sugar in the nectar secreted by one flower: P. cerasus (1.1 mg) < P. avium (1.3 mg) < P. armeniaca (2.4 mg) < P. domestica (2.8 mg) < P. persica(3.6 mg). The flowers secret nectar in which hexoses are predominant (P. armeniaca and P. persica), or hexose-rich nectar (P. domestica), or with a dominant content of sucrose (P. cerasus and P. avium). In terms of the mass of pollen produced per 10 flowers, the investigated species are ranked as follows in increasing order: P. cerasus (7,0 mg) < P. avium (8,1 mg) < P. domestica (11.7 mg) < P. armeniaca (16,5 mg) < P. persica (18.4 mg). The good nutritional value of pollen grains is evidenced by their significant protein content (26.7–34.4%) and rich composition of amino acids. The results obtained in this study on the structure of the nectaries of plants of the genus Prunus contribute new information to taxonomy, anatomy, and flowering biology. The amount and quality of nectar as well as the weight of pollen produced by flowers of the studied representatives of the genus Prunus and pollen protein contents determined in the present study are of great importance for beekeeping. The present study shows that the most valuable species in terms of nectar sugar content and of the highest weight of pollen produced per flower it is Prunus persica. Flowers of plants of the genus Prunus are a valuable pollen and nectar source for honey bees.