Antibiotics,Sugars, and Amino Acids in Nectar of Rhododendron and Piptanthus Species from Nepal

Nectars were extracted in Helambu and Langtang Nepal Himalayas from Rhododendron arboreum and Rh. barbatum (Ericaceae), and from Piptanthus nepalensis (Fabaceae), and analyzed for sugars, amino acids, and antibiotic activity. Sugar content in Rhododendron nectar varied from 17 to 65%. In most nectars, G and F were present in a 1:1 ratio. In addition, from a Rh. arboreum nectar, S could be detected. Piptanthus nectar showed a very high sugar content (up to 80%), F and G, or F, G, and S, respectively, being the main sugar constituents. In all Rhododendron nectar amino acids could be found. In Piptanthus nectar there were no traceable amino acids. Neither an evolutionary significance of amino acid contents in floral nectar nor their close correlation with bees, the main pollinators of both genera, could be confirmed from our studies. Rhododendron nectar showed antibiotic activity due to the presence of acetylandromedol. The biological significance of acetylandromedol, the main toxic principle from Rhododendron nectar, seems to be its antibiotic activity, which could possibly compensate for lower sugar contents in preventing bacterial growth.