Slow carboxylation of R ubisco constrains the rate of carbon fixation during A ntarctic phytoplankton blooms
Summary High‐latitude oceans are areas of high primary production despite temperatures that are often well below the thermal optima of enzymes, including the key C alvin C ycle enzyme, R ibulose 1,5 bisphosphate carboxylase oxygenase ( R ubisco). We measured carbon fixation rates, protein content an...
Saved in:
Published in | The New phytologist Vol. 205; no. 1; pp. 172 - 181 |
---|---|
Main Authors | , , , , |
Format | Journal Article |
Language | English |
Published |
01.01.2015
|
Online Access | Get full text |
Cover
Loading…
Summary: | Summary
High‐latitude oceans are areas of high primary production despite temperatures that are often well below the thermal optima of enzymes, including the key
C
alvin
C
ycle enzyme,
R
ibulose 1,5 bisphosphate carboxylase oxygenase (
R
ubisco).
We measured carbon fixation rates, protein content and
R
ubisco abundance and catalytic rates during an intense diatom bloom in the
W
estern
A
ntarctic
P
eninsula (
WAP
) and in laboratory cultures of a psychrophilic diatom (
F
ragilariopsis cylindrus
).
At −1°C, the
R
ubisco turnover rate,
k
cat
c
, was 0.4 C s
−1
per site and the half saturation constant for
CO
2
was 15 μM (vs
c
. 3 C s
−1
per site and 50 μM at 20°C). To achieve high carboxylation rates, psychrophilic diatoms increased
R
ubisco abundance to
c
. 8% of biomass (vs
c
. 0.6% at 20°C), along with their total protein content, resulting in a low carbon : nitrogen ratio of
c
. 5.
In psychrophilic diatoms,
R
ubisco must be almost fully active and near
CO
2
saturation to achieve carbon fixation rates observed in the
WAP
. Correspondingly, total protein concentrations were close to the highest ever measured in phytoplankton and likely near the maximum possible. We hypothesize that this high protein concentration, like that of
R
ubisco, is necessitated by slow enzyme rates, and that carbon fixation rates in the
WAP
are near a theoretical maximum. |
---|---|
ISSN: | 0028-646X 1469-8137 |
DOI: | 10.1111/nph.13021 |