Determination of 14C Distribution in Photosynthetic Serine and Phosphoglycerate from Grape Leaves

Abstract
Serine and phosphoglyceric acid are the classical marker intermediates of photorespiration and reductive C assimilation in C3 plants. A new and fast method was presented for the determination of 14C distribution in these compounds by selective elimination of C-3 (NaIO4) or C-1 (ninhydrin/ceric sulfate). Reproducibility of the procedure was better than .+-.1% upon degradation of [U-14C]serine and [U-14C]glycerate standards. Determination of labeling patterns in (dephosphorylated) phosphoglycerate and serine, extracted from grape leaf discs after administration of 14CO2 for 1 min showed that 14C distribution in serine changes considerably with changing assimilatory conditions. Interpretations of data basing on unusual labeling patterns of serine must therefore be accepted with caution.