Figure 3.

APR activity after addition of different nitrogen compounds. Arabidopsis plants were cultivated for 72 h without a nitrogen source, fresh media containing different nitrogen sources were added, and plants were cultivated for additional 24 h. APR activity was measured in leaf and root extracts 4, 8, and 24 h after treatment with 4 mm NO₃⁻ (●), 4 mm NH₄⁺ (▪), 4 mm Gln (▴), or 1 mm OAS (▾), as well as in controls (○) and plants cultivated without nitrogen (□). Mean values ± sd from five to nine measurements are shown. Time point 0 corresponds to 72 h without nitrogen.