Rapid recycling of triose phosphates in oak stem tissue

We report the carbon‐13 and oxygen‐18 isotope ratios in cellulose from the early and late wood of pedunculate oak ( Quercus robur L.). The δ 13 C value of the early wood correlates best with that of the late wood of the previous year. The δ 18 O value of the early wood correlates best with that of the late wood of the same year. We suggest that a biochemical explanation of these data is that there is a rapid cycle between hexose monophosphates and triose phosphates in oak stem tissue during cellulose synthesis. Evidence in support of this explanation is provided by the intramolecular distribution of 14 C in labelled fructose extracted from cores of wood that had been supplied with [1− 14 C]‐ and [6‐ 14 C]glucose.