Multilevel Analysis of Primary Metabolism Provides New Insights into the Role of Potassium Nutrition for Glycolysis and Nitrogen Assimilation in Arabidopsis Roots

Reversibility of metabolite changes induced by low K. A, Changes in metabolite concentrations in roots and shoots of 2-week-old Arabidopsis plants grown in low-K (–K) medium for 14 d and subsequently resupplied with K (+K) for 24 h. Changes are in relation to corresponding values measured in plants grown in control medium. Colors and shading are as in Figure 1. B, Absolute concentrations of selected metabolites in the roots of plants grown in control medium (black bars), –K medium (white bars), and –K medium with K added for 24 h (gray bars). Data are means from at least three independently grown and treated plant batches, each of which comprised approximately 100 plants. Raw data and statistics are supplied in Supplemental Table S2. (Note that PEP concentrations were close to the detection limit, so relative changes shown in A should be viewed with caution.) Ac. CoA, Acetyl-CoA; FW, fresh weight; 3PGA, 3-phosphoglycerate; Pyr, pyruvate.

Changes in maximal enzyme activities under low K and K resupply. A, Changes in maximal enzyme activities in roots and shoots of 2-week-old Arabidopsis plants grown in low-K (–K) medium for 14 d and subsequently resupplied with K (+K) for 24 h. Changes are in relation to corresponding values measured in plants grown in control medium. Colors and shading are as in Figure 1. B, Absolute activities of selected enzymes (in nmol min⁻¹ g⁻¹ fresh weight [FW]) in the roots and shoots of plants grown in control medium (black bars), –K medium (white bars), and –K medium with K added for 24 h (gray bars). Data are means from three independently grown and treated plant batches, each of which comprised approximately 100 plants. Raw data and statistics are supplied in Supplemental Table S2. Ac. Inv., Acid invertase; AGPase, ADP-Glc pyrophosphorylase invertase; AlaAT, alanine aminotransferase; AspAT, aspartate aminotransferase; cFBPase, cytosolic Fru biphosphatase; FrucK, fructokinase; GlucK, glucokinase; G6PDH, Glc-6-P dehydrogenase; IDH, isocitrate dehydrogenase; PEPCase, PEP carboxylase; PFP, pyrophosphate-dependent phosphofructokinase; ShikDH, shikimate dehydrogenase.

Intracellular K concentrations and pH in epidermal root cells of low-K Arabidopsis plants. A, Distribution frequency of intracellular concentrations of K determined in 2-week-old plants by impalement with K-selective microelectrodes (n = 37 plants). B, Distribution frequency of intracellular pH determined by impalement with pH-selective microelectrodes (n = 20 plants). C, K concentration and pH within a particular range of simultaneously measured membrane potentials. Means ± se of measurements in individual plants are shown in black for K (mm) and in white for pH.

Electric charges provided by inorganic ions and metabolites. Charge concentration was calculated by multiplying metabolite concentration (as listed in Supplemental Table S1) by the overall charge of the molecule. Plants and growth conditions were as described for Figure 1. A, Charges based on tissue concentrations. These are dominated by the vacuolar lumen. B, Predicted charges in the cytoplasm calculated according to published data for relative cytoplasmic/vacuolar concentrations and volume (see “Materials and Methods”).

Effect of K deficiency on the C-N ratio of amino acids. C-N ratios of all measured amino acids (A and C) and total amino acid concentrations (B and D) in shoots (A and B) and roots (C and D) of plants growing in control (black bars) and low-K (white bars) medium over the indicated course of time are shown. Plants and growth conditions are as described for Figure 1. C and N concentrations were calculated by multiplying the number of C and N atoms in each amino acid (AA) by the concentration of the respective amino acid (as listed in Supplemental Table S1). FW, Fresh weight.