Figure 2.

Phenotypic Characterization of Adult cipk23 Plants and Short-Term (6 min/30 min) High (0.5 mM) and Low (5 mM) Affinity Uptake of ¹⁵N-Labeled Ammonium.

(A) Rosette size of wild-type and cipk23 plants cultivated hydroponically for 6 weeks in HL with 1 mM NH₄NO₃ under elevated potassium conditions (5 mM potassium).

(B) Shoot dry weight of 6-week-old plants. Data are shown as means ± sd; n ≥ 60.

(C) Nitrogen concentration in the shoots of wild-type (WT) and cipk23 plants. Data are shown as means ± sd; n ≥ 30. DW, dry weight.

(D) Potassium content in the shoots of wild-type and cipk23 plants under elevated potassium conditions. Significance tested with t test and indicated by A and B. P < 0.001; n = 15.

(E) to (H) Six-week-old plants were grown hydroponically under continuous supply of 1 mM ammonium nitrate and then deprived of nitrogen for 4 d (−N). After 4 d, half of the plants were resupplied with 2 mM NH₄⁺ [1 mM (NH₄)₂SO₄] for 30 min (+NH₄⁺). N-starved plants and plants after ammonium resupply were moved to the HL solution containing 0.5/5 mM ¹⁵N [0.25/2.5 mM (¹⁵NH₄)₂SO₄] for (E) and (G) 6 min or (F) and (H) 30 min. cipk23, CIPK23 knockout plant; CIPK23#1 and CIPK23#3, complementation lines 1 and 3, respectively. Data are shown as means ± sd. Different uppercase and lowercase letters indicate significant differences between conditions within individual lines at the P value < 0.05 level, ***P value < 0.001, **P value < 0.01; ns, not significant; n = 6.