Figure 6.

Nitrate allocation at nodes is modulated in nrt1.13. Nitrate allocation assay of plants supplied with 2 mM or 0.2 mM ¹⁵${\text{NO}}_3^{-}$. The ¹⁵N concentration of the basal cauline leaf (CL1), the stem of the basal cauline branch (BS1), and the internode between the basal node and second node (IN2) was determined as described in the Methods. Values are means of 21, 26, 17, and 28 independent plants of Col-0 (2 mM), nrt1.13 (2 mM), Col-0 (0.2 mM), and nrt1.13 (0.2 mM), respectively. (A) The ¹⁵N content in CL1, IN2, and BS1 of plants grown with 2 mM or 0.2 mM nitrate. Values are means ± SE (*, P < 0.05, Student’s t-test, compared with Col-0; Supplemental Data set 1). (B) The relative ratio of ¹⁵${\text{NO}}_3^{-}$ accumulation in CL1, BS1, and IN2. The relative ratio is calculated as the amount of ¹⁵N in each part divided by the total amount of ¹⁵N found in all three parts. (*, P < 0.05, Student’s t-test, compared with Col-0; Supplemental Data set 1). (C) Model of nitrate allocation in Col-0 (white arrow) and nrt1.13 (grey arrow) under normal (2 mM) and low (0.2 mM) nitrate conditions.