Photoinactivation of Photosystem II in Prochlorococcus and Synechococcus.

The marine picocyanobacteria Synechococcus and Prochlorococcus numerically dominate open ocean phytoplankton. Although evolutionarily related they are ecologically distinct, with different strategies to harvest, manage and exploit light. We grew representative strains of Synechococcus and Prochlorococcus and tracked their susceptibility to photoinactivation of Photosystem II under a range of light levels. As expected blue light provoked more rapid photoinactivation than did an equivalent level of red light. The previous growth light level altered the susceptibility of Synechococcus, but not Prochlorococcus, to this photoinactivation. We resolved a simple linear pattern when we expressed the yield of photoinactivation on the basis of photons delivered to Photosystem II photochemistry, plotted versus excitation pressure upon Photosystem II, the balance between excitation and downstream metabolism. A high excitation pressure increases the generation of reactive oxygen species, and thus increases the yield of photoinactivation of Photosystem II. Blue photons, however, retained a higher baseline photoinactivation across a wide range of excitation pressures. Our experiments thus uncovered the relative influences of the direct photoinactivation of Photosystem II by blue photons which dominates under low to moderate blue light, and photoinactivation as a side effect of reactive oxygen species which dominates under higher excitation pressure. Synechococcus enjoyed a positive metabolic return upon the repair or the synthesis of a Photosystem II, across the range of light levels we tested. In contrast Prochlorococcus only enjoyed a positive return upon synthesis of a Photosystem II up to 400 µmol photons m-2 s-1. These differential cost-benefits probably underlie the distinct photoacclimation strategies of the species.

Terms used to describe pediatric videofluoroscopic feeding studies: a Delphi survey.

BACKGROUND: The prevalence of pediatric feeding and swallowing disorders is high in the special needs population. Videofluoroscopic feeding studies (VFFS) are used to assess feeding, but the accurate interpretation of VFFS depends on consistent use of terminology for describing a physiological swallow. No consensus exists regarding the terminology used for reporting VFFS findings. PURPOSE: The goal of this study was to achieve consensus among pediatric therapists on definitions for terminology used to describe the results of VFFS. METHODS: Using a Delphi process, therapists from British Columbia rated definitions most appropriate for each term. They also were asked to add definitions that they thought would more accurately describe the terms. FINDINGS. Consensus was achieved on at least one definition for each of the terms used to describe the results of VFFS. IMPLICATIONS: Accurate interpretation of swallowing issues may improve the care of infants and children with feeding and swallowing difficulties.