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Rubisco is a small fraction of total protein in marine phytoplankton
Author(s) -
Losh Jenna L.,
Young Jodi N.,
Morel François M. M.
Publication year - 2013
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/nph.12143
Subject(s) - phytoplankton , rubisco , nutrient , biology , botany , nitrogen , sink (geography) , phosphorus , chemistry , photosynthesis , ecology , cartography , organic chemistry , geography
Summary Ribulose 1,5 bisphosphate carboxylase oxygenase ( R ubisco) concentrations were quantified as a proportion of total protein in eight species of microalgae. This enzyme has been assumed to be a major fraction of total protein in phytoplankton, as has been demonstrated in plants, potentially constituting a large sink for cellular nitrogen. Representative microalgae were grown in batch and continuous cultures under nutrient‐replete, nitrogen ( N )‐limited, or phosphorus ( P )‐limited conditions with varying CO 2 . Quantitative W estern blots were performed using commercially available global antibodies and protein standards. Field incubations with natural populations of organisms from the coast of C alifornia were conducted under both nutrient‐replete and N ‐limited conditions with varying CO 2 . In all experiments, R ubisco represented < 6% of total protein. In nutrient‐replete exponentially growing batch cultures, concentrations ranged from 2% to 6%, while in nutrient‐limited laboratory and field cultures, concentrations were < 2.5%. R ubisco generally decreased with increasing CO 2 and with decreasing growth rates. Based on a calculation of maximum R ubisco activity, these results suggest that phytoplankton contain the minimum concentration of enzyme necessary to support observed growth rates. Unlike in plants, R ubisco does not account for a major fraction of cellular N in phytoplankton.