| Summary: | 碩士 === 國立臺灣大學 === 植物學研究所 === 91 === Water bloom resulted from Peridinium bipes, a freshwater dinoflagellate, has commonly occurred in Dergie dam of the mid of Taiwan. Allelopathic activity was found in the water-soluble extracts of this alga. This study is aimed to study the toxic effects and to characterize the allelochemicals. Seven of thirteen strains of phytoplankton tested were susceptible to the water-soluble extracts of P. bipes. A further study done with Microcystis aeruginosa showed that the photosynthetic O2-evolution and electron transfer between photosystems I and II, but not the respiration, were inhibited in the presence of extracts. This agreed with the phenomenon of the enhancement in the emission of PSII fluorescence when the extract was added to M. aeruginosa cells.
The treatment with P. bipes extract has caused the concentration- and time-dependent reductions in uranine accumulation in M. aeruginosa cells, associated with a significant and rapid leakage of K+ from intra- to extra-cellular medium. This was considered a phenomenon of damage in membrane integrity of the treated cells. As a result, a change in the membrane permeability along with a loss in the pH gradient across the plasma membranes might occur.
Further study was done to test the inhibition of proteases in vitro by the presence of P. bipes extracts. Among 11 proteases tested, thrombin was the most sensitive one. When the extracts were further purified by centricon and centriprep, the fractions with toxic activity were found at those <3 kD. From them, three fractions were obtained when purified with ion chromatography. These fractions showed positive reaction with protein staining, suggesting that they were peptides.
Although P. bipes seems to be cable of producing various kinds of inhibitors, present study suggests that peptide is one of such compounds accounting for allelopathic effects. The primary effects of such allelochemicals seem to act on the plasma membranes of the target algal cells and to inhibit the proteases of the predators.
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