Table 3.

Labeling of amino acid fractions in leaves fed ${}^{13}{\text{NH}}_4^{+}$ through the petiole after 15 minutes and held in nutrient solution. Entire leaves were cut from 3 replicates of tobacco plants that were 6 weeks old grown in soil in a 16/8 walk in growth room at 26^°C with light at about 500 microEinsteins. Incorporation is expressed as a percentage of the label input plus or minus the range detected among 3 individual plant replicates and three measurement replicates.

	GUS	GDH10	BAR
Glu	29.7 + 4.0	18.6 + 2.7	23.4 + 3.1
Gln	18.8 + 6.0	12.0 + 1.1	16.3 + 3.3
${\text{NH}}_4^{+}$	51.3 + 4.3	69.5 + 1.8	51.3 + 2.5