Supported by U.S. Atomic Energy Commission Contract No. AT(11-1)GEN 10, P.A. 20.
Article first published online: 27 APR 2007
Journal of Phycology
Volume 4, Issue 2, pages 151–156, June 1968
How to Cite
Eppley, R. W. and Coatsworth, J. L. (1968), UPTAKE OF NITRATE AND NITRITE BY DITYLUM BRIGHTWELLII-KINETICS AND MECHANISMS. Journal of Phycology, 4: 151–156. doi: 10.1111/j.1529-8817.1968.tb04689.x
Received February 10, 1968; revised March 27, 1968.
- Issue published online: 27 APR 2007
- Article first published online: 27 APR 2007
Ditylum brightwellii grown on NO2- as a nitrogen source took up and assimilated NO2- only in the light, apparently via a photosynthetic nitrite reductase. Assimilation was inhibited by dichlorophenyldimethylurea (DCMU), KCN, partially by 2,4 dinitrophenol, and by NO3-. Kinetics of inhibition of NO2- assimilation by NO3- appeared to be “competitive.” D. brightwellii cells grown on NO2- took up NO3- in both light and dark and in both cases the uptake was inhibited by p-chloromercuribenzoate, but not by DCMU, KCN, or by NO2-. Most of the NO3- taken up in the dark was recovered unchanged from the cells. However only 40% of NO3- taken up in light was recovered from the cells and no NO2- was found. This suggests that a photosynthetic nitrate reduction mechanism was active in these cells. DCMU inhibited the light-induced NO3- reduction. This mechanism of NO3- reduction is distinct from that involving NADH nitrate reductase in D. brightwellii since the concentration of the latter enzyme is very low in cells grown on NO2-. Saturation kinetics were observed for NO2- and NO3- uptake. Half-saturation concentrations (Ksvalues) were 4 and 2 μM, respectively. These values are compared with those obtained for NO2- and NO3- assimilation by other unicellular algae. The comparisons show lower Ksvalues in oceanic species compared with tide-pool or freshwater algae and they support the idea that Ksvalues for NO3- assimilation may provide a key to understanding species succession when this is due to declining: nitrate concentrations in the sea.