IMMUNOLOCALIZATION OF NITRATE REDUCTASE IN THE MARINE DINOFLAGELLATE GONYAULAX-POLYEDRA (PYRROPHYTA)

A polyclonal antibody, raised against nitrate reductase (NR) purified from the photosynthetic dinoflagellate Gonyaulax polyedra Stein, was u sed as a probe in immunogold-labeling experiments on thin sections pre pared from cells harvested both during day and night phases. Previous experiments have shown that both NR activity and the amount of immunor eactive NR in cell extracts is greater when day-phase cells are examin ed, and this property was exploited as an internal control for the cyt ochemical labeling. We observed that in day-phase cells, chloroplasts contained approximately three times more gold particles than night-pha se cells (highly significant difference; P < 0.0001), whereas cytoplas mic labeling levels remained relatively level between day and night. W e conclude from the diurnal level between day and night. We conclude f rom the diurnal difference in labeling that our antibody faithfully re flects the distribution of NR in Gonyaulax cells. Thus, as in to some other higher plants and green algae, Gonyaulax compartmentalizes activ e NR in its chloroplasts.