Carbon fixation and oxygen evolution by phytoplankton in the Canadian high arctic

Summary In the Canadian high arctic, in summer, in situ profiles of oxygen evolution and carbon fixation by phytoplankton showed excellent qualitative and quantitative agreement with an apparent photosynthetic quotient in the range from 1.3 to 1.8. Water column photosynthesis was linear in the available light at the surface. Daily rates photosynthesis exceeded 1 mg C m^-2 d^-1, implying a minimal estimate for annual production in the range from 35 to 70 g C m^-2 y^-1.     

Ultrastructural changes in the Golgi apparatus and secretory granules of HL-60 cells treated with the imino sugar N-butyldeoxynojirimycin

The imino sugar N-butyldeoxynojirimycin inhibits the N-linked oligosaccharide processing enzymes α-glucosidases I and II, and the ceramide specific glucosyltransferase which catalyses the first step in glucosphingolipid biosynthesis. We have studied the effects of this compound on the ultrastructure of HL-60 cells to identify novel activities of this compound. Treatment of HL-60 cells with this imino sugar results in several morphological changes within the cell, none of which result in cytotoxicity. The plasma membrane stains heavily with potassium ferrocyanide within 30 min following addition of the compound to the medium, and there is then a time dependent involvement of all other intracellular membranes. Secretory granules become enlarged and lose their dense core morphology and appear either empty and vacuolated or have low density contents. However, the most striking effect of NB-DNJ treatment is on the Golgi apparatus. The Golgi exhibits a time-dependent change from typical Golgi morphology to a structure almost completely devoid of cisternae and consisting predominantly of vesicles. All the observed changes are fully reversible on withdrawal of the compound.