This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by Chang, K. Articles by Roberts, J. K. M. Search for Related Content PubMed PubMed Citation Articles by Chang, K. Articles by Roberts, J. K. M. Agricola Articles by Chang, K. Articles by Roberts, J. K. M.

Metabolism and Enzymology

Quantitation of Rates of Transport, Metabolic Fluxes, and Cytoplasmic Levels of Inorganic Carbon in Maize Root Tips during K⁺ Ion Uptake ¹

Department of Biochemistry, University of California, Riverside, California 92521

Our aim was to determine whether fixation of inorganic carbon (C_i), due to phosphoenolpyruvate carboxylase activity, is limited by the availability of C_i in the cytoplasm of maize (Zea mays L.) root tips. Rates of C_i uptake and metabolism were measured during K₂SO₄ treatment, which stimulates dark C_i fixation. ¹³C_i uptake was followed by ¹³C-nuclear magnetic resonance (NMR); 5 millimolar K₂SO₄ had no significant effect on ¹³C_i influx. The contribution of respiratory CO₂ production to cytoplasmic HCO₃^– was measured using in vivo ¹³C-NMR and ¹H-NMR of cell extracts; K₂SO₄ treatment had no effect on respiratory CO₂ production. The concentration of cytoplasmic HCO₃^– was estimated to be approximately 11 millimolar, again with K₂SO₄ having no significant effect. These experiments allowed us to determine the extent to which extracellularly supplied ¹⁴C_i was diluted in the cytoplasm by respiratory CO₂ and thereby measure phosphoenolpyruvate (PEP) carboxylase activity in vivo using ¹⁴C_i. PEP carboxylase activity in root tips was enhanced approximately 70% over controls within 12 minutes of the addition of 5 millimolar K₂SO₄. The activity of carbonic anhydrase, which provides PEP carboxylase with C_i, was determined by saturation transfer ¹³C-NMR to be more than 200 times that of PEP carboxylase in vivo. The regulation of PEP carboxylase in K₂SO₄-treated roots is discussed.

This article has been cited by other articles:

				L. H. Wegner and U. Zimmermann Bicarbonate-Induced Alkalinization of the Xylem Sap in Intact Maize Seedlings as Measured in Situ with a Novel Xylem pH Probe Plant Physiology, November 1, 2004; 136(3): 3469 - 3477. [Abstract] [Full Text] [PDF]

				S. Edwards, B.-T. Nguyen, B. Do, and J. K.M. Roberts Contribution of Malic Enzyme, Pyruvate Kinase, Phosphoenolpyruvate Carboxylase, and the Krebs Cycle to Respiration and Biosynthesis and to Intracellular pH Regulation during Hypoxia in Maize Root Tips Observed by Nuclear Magnetic Resonance Imaging and Gas Chromatography-Mass Spectrometry Plant Physiology, March 1, 1998; 116(3): 1073 - 1081. [Abstract] [Full Text]