RNA and DNA concentrations were measured by a modification of the ethidium bromide method in batch cultures of marine phytoplankton and in natural plankton populations (1 to 333 v) from Dabob Bay, Washington State, USA, in spring and summer of 1981. In the cultures the DNA/C ratio remained nearly constant during all phases of growth and growth rate was linearly related to the RNA/DNA ratio. The DNA/C ratio and the relationship between growth rate and RNA/DNA ratio for cultures was used to estimate the amount of living biomass and the growth rates for plankton populations of Dabob Bay. The amount of living carbon was never < 57 % of the total particulate carbon and average growth rates ranged from (0.3 divisions d-' to >4 divisions d-'. Some of the potential problems with such calculations, for example, occurrence of detrital DNA, variability in the D N N C ratio for different groups of organisms, and differences in the relationship between growth rate and RNA/DNA ratio, are discussed. However, these problems may not be major obstacles to using DNA concentrations and RNNDNA ratios for answering major questions in biological oceanography.

No abstract

Relat~ve in wtro actlv~ty levels for the enzyme glutamate synthase (COGAT) with the cofactors NADH NADPH and reduced ferredoxln were determined wlth a I4C method in 6 specles of phytoplankton from 3 taxonomic classes The NADH form of the enzyme was the dominant isozyme in all of the marlne and estuanne specles, whde the ferredoxln form was dominant in the 1 fresh-water species tested Significant amounts of an NADPH specific GOCAT were not detected In any of the orgalusms A sensihve fluorometnc assay for m wtro measurements was subsequently u a z e d to determme the substrate lunetics, pH ophmum and temperature-dependent activation energy for NADH-GOGAT m the diatom Skeletonema costatum Good agreement was obtained with the optlmal m wtro assay condit~ons for achvlty measurements of NADH-GOGAT on a conlmon phytoplankton extract with the I4C and fluorometnc assay methods The sensitlvltles of the 2 assays (l e fluorometric and "C) make them suitable for apphcatlon in studies of nltrogen asslmilat~on and phytoplankton growth rate dynamcs in aquatic ecosystems

No abstract

Glutamine synthetase (GS) is a key enzyme in the assimilation of combined inorganic nitrogen in marine microalgae. Consequently, the development of a sensitive assay technique for GS measurements can have important applications for studies of nitrogen metabolism in both laboratory cultures and field populations of phytoplankton. Bressler & Ahmed (1984) have documented an in vltro assay technique for measurements of biosynthetic GS activity in a variety of marine phytoplankton species. To enhance the general applicability of this procedure, several modifications have been made to increase both the detection capability for the inorganic phosphate end product (P,) and the recovery of total enzyme activity from phytoplankton samples. These improvements have resulted in an approximate 50-fold increase in the overall detection capability for the enzyme, and should accelerate the interest in the use of this enzyme as a sensitive tool in physiological and ecological studies.