Flowering and nectar characteristics of Tilia amurensis, T. mandshurica and T. insularis
2018
Kim, M. S. | Lee, A. S. | Kang, D. B. | Kim, S. H.
Floral nectar is secreted by the nectary which is composed of the epidermis, glandular tissue and nectary parenchyma cells, and located on various floral parts. Nectar which helps entomophilous plants with pollination is the key reward to pollinators. Therefore, plants and pollinators have a symbiotic relationship. The path of nectar secretion flows through the modified stomata distributed in nectary area and the mechanism of secretion starts from phloem sap. Before, during, and after nectar secretion, the sucrose stored in nectary parenchyma cells is hydrolyzed by invertase. Nectar is primarily composed of water, sugar, amino acid, protein, organic acid, mineral, and vitamin. Furthermore, nectar sugar is comprised of sucrose and hexoses (glucose and fructose). Amino acids represent a smaller part of total nectar composition compared to sugar. However, they play a key role determining the taste of nectar. In this research, the flowering time, sugar and amino acid content of Tilia amurensis, T. mandshurica and T. insularis were investigated. Free sugar content and sucrose/hexose ratio varied according to the species (T. amurensis: 39.5±18.6 μg μL(-1) and 1.1; T. mandshurica: 18.2±3.5 μg μL(-1) and 1.2; T. insularis: 18.2±7.4 μg μL(-1) and 1.4). Although three species showed different flowering periods and similar flower size, T. amurensis showed the highest free sugar content. Flower size of three Tilia species was 1 cm averagely. Since these flowers are pollinated by small pollinators such as honeybees and flies requiring relatively low energy, evolutionarily, Tilia floral nectar might produce relatively few sugars. In addition, proline which taste can be detected by insects such as honeybees was the most abundant (27.4~45.8%) in the three species.
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