Oxalate metabolism by tobacco leaf discs [Formation from glyoxylate, decarboxylation, photorespiratory carbon dioxide formation]

The turnover rate of oxalate in leaf discs of Nicotiana tabacum, var Havana Seed, during photosynthesis was estimated to be 1 to 2 micromoles per gram fresh weight per hour. Radioactivity from the enzymic oxidation of [14C]oxalate rapidly appeared in neutral sugars (mainly sucrose), organic acids (mainly malate), and amino acids. Only 5% of the radioactivity was released to the atmosphere as 14CO2, and no formate or formaldehyde could be detected. The metabolism of oxalate was not increased by raising the O2 concentration from 1% to 21% to 60%, nor was the formation of [14C]oxalate from [2-14C]glyoxylate changed under the same conditions as was previously observed in vitro (Havir 1983 Plant Physiol 71: 874-878). While oxalate is not an inert end product of the glycolate pathway, it contributes little to the formation of photorespiratory CO2.