| Budget Amount *help |
¥3,700,000 (Direct Cost: ¥3,700,000)
Fiscal Year 1998: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1997: ¥3,000,000 (Direct Cost: ¥3,000,000)
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| Research Abstract |
Inhibitory effects of macrophytes on the growth of blue-green algae (Microcystis aeruginosa and other two species) were assayed in a mixed culture system with various concentrations of macrophytes, i.e., coexistence assay. Myriophyllum spicatum, Cabomba caroliniana and other 7 species were used as macrophytes. The coexistence assay showed that, among the 9 macrophytes, C.caroliniana and M.spicatum were the only species to inhibit growth of all the species of blue green algae. The inhibitory effects of M.spicatum were stronger than those of C.caroliniana.
Due to its strong inhibition, we used the culture solution of M.spicatum for an algal assay to confirm that the inhibitory effect of M.spicatum is caused by allelopathic compounds secreted from M.spicatum. The growth of M.aeruginosa was significantly inhibited by the quasi-continuous addition of the culture solution of M.spicatum, whereas the initial addition did not inhibit their growth. Such results provide the evidence of the allelop
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athic compounds, which must be continuously secreted by M.spicatum.
Next, we searched for allelopathic compounds in the culture solution of M.spicatum using an analytical High Performance Liquid Chromatography (HPLC). The analytical HPLC revealed four allelopathic compounds (pyrogallic acid, gallic acid, (+)-catechin and ellagic acid), which were confirmed to be inhibitory to M.aeruginosa and susceptible to autoxidation, in the culture solution of M.spicatum. A comparison between the inhibitory effects of each compounds and those of a mixture of the four compounds showed that the mixture induced synergistic inhibitory effects on M.aeruginosa.
In order to verify whether or not the identified compounds determined in the culture solution of M.spicat urn contribute to the allelopathic effects of M.spicatum, the amounts of the four compounds released by M.spicatum were calculated to compensate loss of the compounds due to auto-oxidation during the cultivation, Based on the calculated amounts, the artificial culture solution of M.spicatum was prepared using the authentic samples of the four compounds. Comparing the inhibitory effects of the artificial culture solution with those of the culture solution of M.spicatum (mentioned above), it was evident that the four compounds contributed to the allelopathic effects of M.spicatum. Less
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