Plant Physiology 75:212-218 (1984)
© 1984 American Society of Plant Biologists
Articles
Fermentative Metabolism of Chlamydomonas reinhardtii1
I. Analysis of Fermentative Products from Starch in Dark and Light
René P. Gfeller2 and
Martin Gibbs
Institute for Photobiology of Cells and Organelles, Brandeis University, Waltham, Massachusetts 02254
The anaerobic starch breakdown into end-products in the green alga Chlamydomonas reinhardtii F-60 has been investigated in the dark and in the light. The effects of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) and carbonyl cyanide-p-trifluoromethoxyphenyl hydrazone (FCCP) on the fermentation in the light have also been investigated.
Anaerobic starch breakdown rate (13.1 ± 3.5 micromoles C per milligram chlorophyll per hour) is increased 2-fold by FCCP in the dark. Light (100 watts per square meter) decreases up to 4-fold the dark rate, an inhibition reversed by FCCP. Stimulation of starch breakdown by the proton ionophore FCCP points to a pH-controlled rate-limiting step in the dark, while inhibition by light, and its reversal by FCCP, indicates a control by energy charge in the light.
In the dark, formate, acetate, and ethanol are formed in the ratios of 2.07:1.07:0.91, and account for roughly 100% of the C from the starch. H2 production is 0.43 mole per mole glucose in the starch. Glycerol, D-lactate, and CO2 have been detected in minor amounts.
In the light, with DCMU and FCCP present, acetate is produced in a 1:1 ratio to formate, and H2 evolution is 2.13 moles per mole glucose. When FCCP only is present, acetate production is lower, and CO2 and H2 evolution is 1.60 and 4.73 moles per mole glucose, respectively.
When DCMU alone is present, CO2 and H2 photoevolution is higher than in the dark. Without DCMU, CO2 and H2 evolution is about 100% higher than in its presence. In both conditions, acetate is not formed. In all conditions in the light, ethanol is a minor product. Formate production is least affected by light.
The stoichiometry in the dark indicates that starch is degraded via the glycolytic pathway, and pyruvate is broken down into acetyl-CoA and formate. Acetyl-CoA is further dissimilated into acetate and ethanol. In the light, acetate is produced only in the presence of FCCP and, when photophosphorylation is possible, it is used in unidentified reactions. Ethanol formation is inhibited by the light in all conditions.
2 Supported partially with grants from Fonds National Suisse de la Recherche Scientifique and Holderbank Stiftung.
1 Supported by Department of Energy DE-ACO2-76-ERO3231 and National Science Foundation PCM 79-22612.
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