Determination of the natural deuterium distribution in glucose from plants having different photosynthetic pathways

Abstract

Abstract 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 C 3 (potato, barley, sunflower, wheat) or C 4 (maize, sorghum) photosynthetic metabolism were investigated. Since the glucose molecule is not suitable for direct SNIF‐NMR analysis, several kinds of derivatives were synthesized. Three clusters of isotopomers were identified in glucose penta‐acetate which is easily prepared. Up to 5–6 sites could be distinguished in 6 other derivatives. An integrated statistical analysis of the whole sets of cluster lines was performed in order to determine the individual isotope contents in the carbon‐bound hydrogen positions of 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 photosynthetic C 3 or C 4 family. Larger deviations with respect to a statistical distribution of deuterium are observed in glucose from C 3 plants as compared to C 4 plants. The methylenic sites 6,6′ in particular are significantly depleted in C 3 glucose as compared to C 4 glucose.