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


 

 
Job task

 

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. 

 

 
Contact:

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