Poster: Photosynthesis
Abs #
325: Hydrogen metabolism in Chlamydomonas reinhardtii Rubisco mutants
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Presenter: |
White, Andrea L, andig14@yahoo.com |
Authors | White, Andrea L (A) Melis, Anastasios (A) | | Affiliations: |
(A): University Of California Berkeley
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Sulfur-deprivation in C. reinhardtii brings about prompt degradation of Rubisco and substantial accumulation of starch. These changes precede H2 photoproduction by the cells. The work investigated cause-and-effect relationships between Rubisco loss, starch accumulation and subsequent H2-production in C. reinhardtii. Two Rubisco mutants were compared to the wild type (WT) in terms of metabolic flux and H2-production upon S-deprivation. One mutant exhibited low levels while the other lacked Rubisco. Changes in starch, protein, chlorophyll, cell density, as well as rates of photosynthesis, respiration and H2-production were monitored upon S-deprivation over a 120 h period. Results showed that starch rapidly accumulates within the first 72 h of S-deprivation in the WT, followed by a gradual breakdown concomitant with H2-production. Cellular protein content followed a similar pattern as starch metabolism in the WT. The Rubisco mutants had lower photosynthesis but comparable respiration rates as the WT. They did not exhibit starch accumulation upon S-deprivation and failed to accumulate H2 gas. The mutants also lacked the low-level initial accumulation of protein. It is concluded that Rubisco plays a central role in H2-production under anaerobic S-deprivation conditions via the facilitated accumulation of starch. These results suggested that a coordinated catabolism of Rubisco and corresponding starch accumulation are critical to the metabolism of H2-production in C. reinhardtii. Starch accumulation and a subsequent gradual breakdown provide the endogenous substrate that supports H2-production, both directly by feeding electrons into the plastoquinone pool in chloroplasts, and indirectly by sustaining mitochondrial respiration for the maintenance of anaerobiosis in the cell.
