DOI: 10.1093/jxb/erf092 Utilization of glycine and serine as nitrogen sources in the roots of Zea mays and Chamaegigas intrepidus

Glycine and serine are potential sources of nitro-gen for the aquatic resurrection plant Chamaegigas intrepidus Dinter in the rock pools that provide its natural habitat. The pathways by which these amino acids might be utilized were investigated by incubating C. intrepidus roots and maize (Zea mays) root tips with [15N]glycine, [15N]serine and [2-13C]glycine. The metabolic fate of the label was followed using in vivo NMR spectroscopy, and the results were consistent with the involvement of the glycine decarboxylase complex (GDC) and serine hydroxymethyltransferase (SHMT) in the utilization of glycine. In contrast, the labelling patterns pro-vided no evidence for the involvement of serine:-glyoxylate aminotransferase in the metabolism of glycine by the root tissues. The key observations were: (i) the release of [15N]ammonium during [15N]-labelling experiments; and (ii) the detection of a characteristic set of serine isotopomers in the [2-13C]glycine experiments. The effects of aminoa-cetonitrile, amino-oxyacetate, and isonicotinic acid hydrazide, all of which inhibit GDC and SHMT to some extent, and of methionine sulphoximine, which inhibited the reassimilation of the ammo-nium, supported the conclusion that GDC and SHMT were essential for the metabolism of glycine. C. intrepidus was observed to metabolize serine more readily than the maize root tips and this may be an adaptation to its nitrogen-de®cient habitat. Overall, the results support the emerging view that GDC is an essential component of glycine catabo-lism in non-photosynthetic tissues