Abstract
Grain density autoradiography was examined as applied to the quantitative determination of photosynthesis by individual phytoplankton species. Silver grains over and around (30μm from the cell margin) algal cells were estimated to be formed by β-emission of 14C incorporated in the cells. The grain count in this area increased linearly with the exposure time and related significantly with the radioactivity of the cells. A good correlation was obtained between grain counts (no./cell) and radioactivity in the cell (dpm/cell). The regression was almost the same in three algal species of a similar small cell size, but considerably lower in a larger species. This indicates that the comparison of absolute radioactivity between different species should be made carefully. By using the autoradiographic technique, photosynthetic characteristics such as light-photosynthetic rate relation could be determined in individual phytoplankton species in a eutrophic pond. The technique appears to be useful especially in detecting species reaction to a change of nutrient conditions in phytoplankton ecology.
