Transgenic tobacco plants that overexpress alfalfa NADH-glutamate synthase have higher carbon and nitrogen content

This work reports the characterization of transgenic tobacco (Nicotiana tabacum L.) plants that constitutively overexpress NADH-GOGAT. Three independent transformants, designated GOS10, GOS13 and GOS19 (for (GO) under bar GAT (s) under bar ense), with stable integration of the chimeric alfalfa NADH-GOGAT gene fused to the CaMV 35S promoter were studied. The transgene was stably integrated and inherited by the progeny. In these GOS lines, the expression of NADH-GOGAT mRNA and protein was detected at low levels in roots and leaves, while the expression of the host tobacco NADH-GOGAT gene was nearly undetectable. The roots of GOS lines showed an elevated (15-40%) enzyme activity as compared to control plants. When GOS plants were grown under greenhouse conditions and fed with either nitrate or ammonium as the sole nitrogen source, they showed higher total carbon and nitrogen content in shoots and increased shoot dry weight when plants were entering into the flowering stage, as compared to control plants. The observed phenotype of GOS plants was interpreted as reflecting a higher capacity to assimilate nitrogen due to a higher NADH-GOGAT activity.