65(P-47) 淡水産緑藻Actinastrum sp.に形態変化をもたらす捕食者ミジンコのカイロモン性物質の探索(ポスター発表の部)

抄録

The behavior of organisms is strictly regulated by chemical substances. They are frequently used between different organisms as chemical signals. Pheromones and allelopathic substances are these cases. Although such substances are well documented for terrestrial organisms, very few are known for aquatic organisms. This paper deals with a kairomone-like substance released by an aquatic crustacean, which affects the morphology of a fresh-water green alga. The green alga Actinastrum sp. is an aquatic microalga (6x5μm) inhabiting in natural water. The morphological form of the cultivated alga is usually a single cell. When a crustacean Daphnia, which feeds on the microalga, is introduced in the cultivation medium, the alga quickly achieves its morphological change and forms colonies composed of two, four, and eight cells. Interestingly, the same phenomenon is observed when the cultivation medium of Daphnia (Daphnia water) was added to the medium in which the green alga grows. This indicates that, a certain substance inducing the morphological change of Actinastrum sp. may exist in Daphnia water. We investigated this kairomone-like substance released by Daphnia. A bioassay system was built-up and chromatographic fractions of Daphnia water were examined by the assay. The active substance seemed to be a carboxylic acid judging from its polarity and its behavior on an ion-exchange resin. Therefore, several simple carboxylic acids, such as acetic acid, butanoic acid, and amino acids, were subjected to the assay. They were, however, all inactive. HPLC separation of Daphnia water using a reverse-phase column (C-18) and MeOH-water as an elution solvent, gave active fractions. The components of the active fractions were investigated by means of NMR and MS spectroscopy.