The Ca2+-Regulation of the Mitochondrial External NADPH Dehydrogenase in Plants Is Controlled by Cytosolic pH

PLoS One. 2015 Sep 28;10(9):e0139224. doi: 10.1371/journal.pone.0139224. eCollection 2015.

Abstract

NADPH is a key reductant carrier that maintains internal redox and antioxidant status, and that links biosynthetic, catabolic and signalling pathways. Plants have a mitochondrial external NADPH oxidation pathway, which depends on Ca2+ and pH in vitro, but concentrations of Ca2+ needed are not known. We have determined the K0.5(Ca2+) of the external NADPH dehydrogenase from Solanum tuberosum mitochondria and membranes of E. coli expressing Arabidopsis thaliana NDB1 over the physiological pH range using O2 and decylubiquinone as electron acceptors. The K0.5(Ca2+) of NADPH oxidation was generally higher than for NADH oxidation, and unlike the latter, it depended on pH. At pH 7.5, K0.5(Ca2+) for NADPH oxidation was high (≈100 μM), yet 20-fold lower K0.5(Ca2+) values were determined at pH 6.8. Lower K0.5(Ca2+) values were observed with decylubiquinone than with O2 as terminal electron acceptor. NADPH oxidation responded to changes in Ca2+ concentrations more rapidly than NADH oxidation did. Thus, cytosolic acidification is an important activator of external NADPH oxidation, by decreasing the Ca2+-requirements for NDB1. The results are discussed in relation to the present knowledge on how whole cell NADPH redox homeostasis is affected in plants modified for the NDB1 gene.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arabidopsis / enzymology*
  • Calcium / metabolism*
  • Cytosol / metabolism*
  • Electrons
  • Hydrogen-Ion Concentration
  • Mitochondria / enzymology*
  • NADP / metabolism
  • NADPH Dehydrogenase / metabolism*
  • Oxidation-Reduction
  • Quinones / metabolism
  • Solanum tuberosum / enzymology*

Substances

  • Quinones
  • NADP
  • NADPH Dehydrogenase
  • Calcium

Grants and funding

This work was supported by The Carl Trygger Foundation for Scientific Research (10:318, 11:381, 12:397; http://www.carltryggersstiftelse.se/); Faculty of Science at Lund University (No grant number). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.