The role of the C4 pathway in carbon accumulation and fixation in a marine diatom

John R Reinfelder, Allen J Milligan, François M M Morel
Plant Physiology 2004, 135 (4): 2106-11
The role of a C(4) pathway in photosynthetic carbon fixation by marine diatoms is presently debated. Previous labeling studies have shown the transfer of photosynthetically fixed carbon through a C(4) pathway and recent genomic data provide evidence for the existence of key enzymes involved in C(4) metabolism. Nonetheless, the importance of the C(4) pathway in photosynthesis has been questioned and this pathway is seen as redundant to the known CO(2) concentrating mechanism of diatoms. Here we show that the inhibition of phosphoenolpyruvate carboxylase (PEPCase) by 3,3-dichloro-2-dihydroxyphosphinoylmethyl-2-propenoate resulted in a more than 90% decrease in whole cell photosynthesis in Thalassiosira weissflogii cells acclimated to low CO(2) (10 microm), but had little effect on photosynthesis in the C(3) marine Chlorophyte, Chlamydomonas sp. In 3,3-dichloro-2-dihydroxyphosphinoylmethyl-2-propenoate-treated T. weissflogii cells, elevated CO(2) (150 microm) or low O(2) (80-180 microm) restored photosynthesis to the control rate linking PEPCase inhibition with CO(2) supply in this diatom. In C(4) organic carbon-inorganic carbon competition experiments, the (12)C-labeled C(4) products of PEPCase, oxaloacetic acid and its reduced form malic acid suppressed the fixation of (14)C-labeled inorganic carbon by 40% to 50%, but had no effect on O(2) evolution in photosynthesizing diatoms. Oxaloacetic acid-dependent O(2) evolution in T. weissflogii was twice as high in cells acclimated to 10 microm rather than 22 microm CO(2), indicating that the use of C(4) compounds for photosynthesis is regulated over the range of CO(2) concentrations observed in marine surface waters. Short-term (14)C uptake (silicone oil centrifugation) and CO(2) release (membrane inlet mass spectrometry) experiments that employed a protein denaturing cell extraction solution containing the PEPCKase inhibitor mercaptopicolinic acid revealed that much of the carbon taken up by diatoms during photosynthesis is stored as organic carbon before being fixed in the Calvin cycle, as expected if the C(4) pathway functions as a CO(2) concentrating mechanism. Together these results demonstrate that the C(4) pathway is important in carbon accumulation and photosynthetic carbon fixation in diatoms at low (atmospheric) CO(2).

Full Text Links

Find Full Text Links for this Article


You are not logged in. Sign Up or Log In to join the discussion.

Related Papers

Remove bar
Read by QxMD icon Read

Save your favorite articles in one place with a free QxMD account.


Search Tips

Use Boolean operators: AND/OR

diabetic AND foot
diabetes OR diabetic

Exclude a word using the 'minus' sign

Virchow -triad

Use Parentheses

water AND (cup OR glass)

Add an asterisk (*) at end of a word to include word stems

Neuro* will search for Neurology, Neuroscientist, Neurological, and so on

Use quotes to search for an exact phrase

"primary prevention of cancer"
(heart or cardiac or cardio*) AND arrest -"American Heart Association"