A 13C NMR study of photosynthate transport and metabolism in the lichen Xanthoria calcicola Oxner

summary 13C nuclear magnetic resonance (NMR) spectroscopy was applied to the lichen Xanthoria calcicola Oxner. The in vivo spectra were poorly resolved and although the line‐broadening effect of variations in the bulk magnetic susceptibility could be eliminated by spinning the sample at the magic angle, the spectra were still relatively Uninformative in comparison with the spectra of methanol extracts of the tissue. The synthesis of ribitol by the algal symbiont and its subsequent metabolism to mannitol by the fungus was followed using pulse‐chase experiments. The fine structure in the spectra provided support for the role of the pentose phosphate pathway in the conversion of ribitol to mannitol. Preliminary experiments, in which the conditions of the pulse‐chase experiment were altered, showed that the incorporation of 13C into mannitol was reduced at a lower temperature, and in thalli of low moisture content, and was abolished by darkness.