Figure 1.

APR and CS activity during nitrogen deficiency. Arabidopsis plants (4.5 weeks old) were transferred onto nutrient solution without a nitrogen source. APR (A) and CS (B) activities were measured at the time points indicated in extracts from leaves and roots of nitrogen-deficient plants (▪) and controls cultivated with 4 mm NO₃⁻ (●). Mean values ± sd from five to nine measurements are shown. The differences in APR activity between nitrogen-deficient and control plants are significant (P < 0.05) from 48 h.