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Algal evolution in relation to atmospheric CO2: carboxylases, carbon concentrating mechanisms and carbon oxidation cycles
John A. RAven, Mario Giordano, John Beardall, Stephen Maberly
Phil. Trans. R. Soc. B (2012) 367, 493-507 doi:10.1098/rstb.2011.0212
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Algal evolution in relation to atmospheric CO2: carboxylases, carbon concentrating mechanisms and carbon oxidation cycles
Oxygenic photosynthesis evolved at least 2.4 Ga; all oxygenic organisms use the ribulose bisphosphate carboxylase-oxygenase (Rubisco)-photosynthetic carbon reduction cycle (PCRC) rather than one of the five other known pathways of autotrophic CO2 assimilation. The high CO2 and (initially) O2 -free conditions permitted the use of a Rubisco with a high maximum specific reaction rate. As CO2 decreased and O2 increased, Rubisco oxygenase activity increased and 2-phosphoglycolate was produced, with the evolution of pathways recycling this inhibitory product to sugar phosphates. Changed atmospheric composition also selected for Rubiscos with higher CO2 affinity and CO2 /O2 selectivity correlated with decreased CO2 -saturated catalytic capacity and/or for CO2 -concentrating mechanisms (CCMs). These changes increase the energy, nitrogen, phosphorus, iron, zinc and manganese cost of producing and operating Rubisco-PCRC, while biosphere oxygenation decreased the availability of nitrogen, phosphorus and iron. The majority of algae today have CCMs; the timing of their origins is unclear. If CCMs evolved in a low-CO2 episode followed by one or more lengthy high-CO2 episodes, CCM retention could involve a combination of environmental factors known to favour CCM retention in extant organisms that also occur in a warmer high-CO2 ocean.
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Prof. Mario Giordano Laboratorio di Fisiologia delle Alghe e delle Piante Dipartimento di Scienze della Vita e dell'Ambiente (ex Scienze del Mare) Università Politecnica delle Marche Via Brecce Bianche Palazzina Scienze 2 60131 Ancona Italy
Phone (office): +39 071 220 4652 Phone (lab.): +39 071 220 4659 Fax: +39 071 220 4650 E-mail: m.giordano@univpm.it
Web site: www.univpm.it
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