On the Mechanisms of Diurnal Vertical Migration Behavior of Heterosigma akashiwo (Raphidophyceae)

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The marine raphidophycean biflagellate, Heterosigma akashiwo, clearly showed diurnal vertical migration under a 12 h light-12 h dark photoperiod appearing at the surface of the culture medium during the light period and at the bottom during the dark period. The upward migration commenced a few hours before the light was turned on and the downward migration a few hours before it was turned off. The diuranal vertical migration behavior was closely correlated with diurnal changes in the specific gravity of the cells, those near the surface of the culture medium had a smaller specific gravity than those at the bottom. The migration behavior was also correlated with the direction of cell swimming. More cells had flagella furrow facing upward than downward in the light phase, and vice versa in the dark phase. Phototaxis was not the main factor inducing the vertical migration, though the cells did show a tactic respose to light. Chemotactic responses to O_2, N_2 or CO_2 gas did not occur.
日本植物生理学会の論文