Comparative Algal and Byrophyte Physiology
Hanson, David T. .
Early land plant adaptations to limitation of photosynthesis by CO2 diffusion.
Limitation of photosynthesis by the rate of CO2 diffusion from the surrounding environment to the site of carboxylation occurs in all types of photosynthetic organisms. Adaptations to minimize this limitation vary widely, however there is a functional divergence between aquatic and terrestrial organisms where direct CO2 and HCO3- pumping is lost, but regulation of diffusional resistance remains. This divergence is not complete or well characterized for many organisms, especially among embryophytes. The evolution of complex metabolic pathways including C4 and CAM photosynthesis among late divergent land plants has been the focus of a large body of work, but these processes are not related to the evolution of early land plants. The middle ground occupied between inorganic carbon pumps and complex metabolic pathways is direct modification of the diffusional pathway between the site of carboxylation and the atmosphere. These modifications can occur at the sub-cellular scale via the presence and form of internal chloroplast protein bodies called pyrenoids, the alteration of membrane permeability, and the size of chloroplasts and their proximity to air spaces, on up to the whole tissue scale via alteration of internal leaf or thallus structure, the size and structure of epidermal pores, and mechanisms for controlling water film thickness. Recent advances in the online analysis of photosynthetic discrimination against 13CO2 relative to 12CO2 have shed new light on the importance of modifying each of these resistive pathways in land plants. I will present a brief history of algal and bryophyte adaptations to diffusional limitation of photosynthesis along with my recent online analyses of photosynthetic discrimination by hornworts, liverworts, and some higher plants. These data will be discussed in the context of recently published phylogenies for early land plant groups in an effort to discuss the evolution of diffusional modifications.
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1 - University of New Mexico, Department of Biology, 167 Castetter Hall, Albuquerque, New Mexico, 87131, USA
Presentation Type: Symposium or Colloquium Presentation
Location: Stevens 4/Hilton
Date: Tuesday, July 10th, 2007
Time: 10:45 AM