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

This work reports the characterization of transgenic tobacco (Nicotiana tab acum L.) plants that constitutively overexpress NADH-GOGAT. Three independe nt 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 s tably integrated and inherited by the progeny. In these GOS lines, the expr ession of NADH-GOGAT mRNA and protein was detected at low levels in roots a nd leaves, while the expression of the host tobacco NADH-GOGAT gene was nea rly undetectable. The roots of GOS lines showed an elevated (15-40%) enzyme activity as compared to control plants. When GOS plants were grown under g reenhouse conditions and fed with either nitrate or ammonium as the sole ni trogen source, they showed higher total carbon and nitrogen content in shoo ts and increased shoot dry weight when plants were entering into the flower ing stage, as compared to control plants. The observed phenotype of GOS pla nts was interpreted as reflecting a higher capacity to assimilate nitrogen due to a higher NADH-GOGAT activity.