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Title: Dark Protein Synthesis: Physiological Response to Nutrient Limitation of a Natural Phytoplankton Population 
Author: Taguchi, Satoru; Laws, Edward A.
Date: 2001-01
Publisher: University of Hawai’i Press
Citation: Taguchi S, Laws EA. 2001. Dark protein synthesis: physiological response to nutrient limitation of a natural phytoplankton population. Pac Sci 55(1): 1-15.
Abstract: Dark 14CO2 incorporation into protein was determined from 24-hr
incubations using size-fractionated natural phytoplankton populations from
Kane'ohe Bay, Hawai'i, enriched with either ammonium or ammonium plus
phosphorus. Response to ammonium addition was maximum at an ammonium
concentration of 3-4 μM. Dark 14C02 assimilation was suppressed by addition
of both ammonium and phosphorus, but percentage incorporation into protein
was not significantly different from addition of ammonium alone. About
75 ± 1% of the 14C taken up by the cells was incorporated into either protein or
low-molecular-weight intermediate compounds. Cells smaller than 10 μm
showed little response to nutrient additions. However, cells in the 10- to 35-μm
size fraction incorporated significantly more 14C into protein when nutrients
were added. C:N ratios calculated from the percentage of 14C incorporated into
protein were most variable temporally in the 10- to 35-μm size group and least
variable in the picoplankton (0.2-2.0 μm). Nutrient limitation indices (NUs)
calculated from the quotient of C:N ratios in control and nutrient-enriched
cultures were not significantly different for the picoplankton and 2- to 10-μm
size fraction. The NLI for the 10- to 35-μm size fraction was significantly lower
and implied a modest degree of nutrient limitation. The results suggest that cells
smaller than 10 μm are growing at close to nutrient-saturated rates much of the
time in Kane'ohe Bay. However, larger cells appear to experience a significant
degree of nutrient limitation at some times, particularly when chlorophyll a
concentrations are less than about 1 mg m-3
• Dark protein synthesis appears to
be a useful modification of previous methods based on the dark uptake of 14C02
for studying nutrient limitation.
ISSN: 0030-8870

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