DETERMINATION OF THE NATURAL DEUTERIUM DISTRIBUTION IN GLUCOSE FROM PLANTS HAVING DIFFERENT PHOTOSYNTHETIC PATHWAYS

The site-specific natural isotope fractionation of hydrogen in glucose was investigated by nuclear magnetic resonance spectroscopy (SNIF-NMR ). Several glucose samples obtained from plants undergoing either C3 ( potato, barley, sunflower, wheat) or C4 (maize, sorghum) photosyntheti c metabolism were investigated. Since the glucose molecule is not suit able for direct SNIF-NMR analysis, several kinds of derivatives were s ynthesized. Three clusters of isotopomers were identified in glucose p enta-acetate which is easily prepared. Up to 5-6 sites could be distin guished in 6 other derivatives. An integrated statistical analysis of the whole sets of cluster lines was performed in order to determine th e individual isotope contents in the carbon-bound hydrogen positions o f the glucose skeleton. Both the mole fractions of the monodeuterated isotopomers and the deuterium/hydrogen ratios of the individual sites thus become accessible. Using this approach, it is, shown that similar trends in the isotopic distribution are exhibited within a given phot osynthetic C3 or C4 family. Larger deviations with respect to a statis tical distribution of deuterium are observed in glucose from C3 plants as compared to C4 plants. The methylenic sites 6,6' in particular are significantly depleted in C3 glucose as compared to C4 glucose.