CO2 in white spruce shoot primordia entering winter dormancy

Feeding [1-C]-guanidinoacetic acid to shoot primordia, O2 uptake was inhibited and major products were C-glycine, CO2 and C-serine. The direct decarboxylation of [1-C]-guanidinoacetic acid to CO2 and N-methylguanidine, the methylation of [1-C]-guanidinoacetic acid to C-creatine, and the lytic cleavage to urea and C-glycine were all ruled out. Enzymatic transamidinations of [1-C]-guanidinoacetic acid with amino acid acceptors occurred as arginine-rich storage proteins were being turned over and new proteins synthesized containing C-glycine and C-serine. The products of transamidination were recycled as substrates until Cglycine was metabolized in different directions and transported to mitochondria and peroxisomes. C-Glycine was decarboxylated by a glycine decarboxylase multienzyme complex resulting in a net carbon loss and a sharp decline in total protein rich in arginine N. Under these conditions, unlabelled arginine and ornithine contributed as substrates for reversible transamidination reactions. Peroxisomes and mitochondria are hypothesized as providing argininederived nitric oxide to maintain redox homeostasis in response to the stresses imposed by [1-C]-guanidinoacetic acid and to protect against the inhibitory activity of sulfhydryls on transamidinase activity. The destruction of a respiratory inhibitor by transamidination may comprise a mechanism associated with the awakening from of dormancy and the mobilization of storage protein reserves in conifers.