IMMUNOLOCALIZATION OF NITRATE REDUCTASE IN THE MARINE DINOFLAGELLATE GONYAULAX POLYEDRA (PYRROPHYTA)¹

Abstract

A polyclonal antibody, raised against nitrate reductase (NR) purified from the photosynthetic dinoflagellate Gonyaulax polyedra Stein, was used as a probe in immunogold‐labeling experiments on thin sections prepared from cells harvested both during day and night phases. Previous experiments have shown that both NR activity and the amount of immunoreactive NR in cell extracts is greater when day‐phase cells are examined, and this property was exploited as an internal control for the cytochemical labeling. We observed that in day‐phase cells, chloroplasts contained approximately three times more gold particles than night‐phase cells (highly significant difference; P < 0.0001), whereas cytoplasmic labeling levels remained relatively level between day and night. We conclude from the diurnal difference in labeling that our antibody faithfully reflects the distribution of NR in Gonyaulax cells. Thus, as in to some other higher plants and green algae, Gonyaulax compartmentalizes active NR in its chloroplasts.

Soluble and membrane‐associated nitrate reductases in the dinoflagellate Peridinium gatunense

“…Immunolocalization of Gonyaulax NR (Fritz et al, 1996) indicated a chloroplastic location, in agreement with previous studies on NR from green algae (Lo! pez-Ruiz et al, 1985) although there is also evidence of soluble NR (sNR) in those organisms (Sto$ hr et al, 1993).…”

Linking chlorophyll-nutrient dynamics to the RedÞeld N:C ratio with a model of optimal phytoplankton growth

“…NR is located partly at the plasmalemma and partly in the cytoplasm in Thalassiosira spp. (Jones & Morel 1988), but NR has also been located in chloroplasts of several dinoflagellates and green algae (Fritz et al 1996). Thus, the dependence of ζ on nitrogen source seen in Fig.…”

Vertical migration of the toxic dinoflagellate Gymnodinium catenatum under different concentrations of nutrients and humic substances in culture

“…Pools were larger in nitrate-deplete cells compared to nitrate-replete cells, suggesting that N-stress caused a decrease in the rate of nitrate assimilation (resulting in a build-up of internal nitrate). Decreased nitrate assimilation may be related to a decrease in nitrate reductase activity, which is affected by light quality (particularly blue versus red light; e.g., Carmona et al, 1996) and quantity (e.g., Fritz et al, 1996), as well as N supply (Sanz et al, 1995). It is likely that HS in surface layers affected all of these factors and thus may have influenced G. catenatum nitrate assimilation.…”