Planta

, Volume 146, Issue 4, pp 481–486 | Cite as

Control of electron flow in intact chloroplasts by the intrathylakoid pH, not by the phosphorylation potential

  • Yoshichika Kobayashi
  • Yorinao Inoue
  • Kazuo Shibata
  • Ulrich Heber
Article

Abstract

In the presence of nitrite or oxaloacetate, intact chloroplasts evolved oxygen at a significant rate for the initial 1 to 2 min of illumination. Subsequently, oxygen evolution was suppressed progressively. The suppressed oxygen evolution was stimulated strikingly by NH4Cl. The results indicate that coupled electron flow in intact chloroplasts is controlled in the light, and the control is released by NH4Cl. However, at low concentrations, NH4Cl was not an effective uncoupler of photophosphorylation in intact chloroplasts. Intrachloroplast ATP levels and ATP/ADP ratios were not significantly influenced by NH4Cl. In contrast, the quenching of 9-aminoacridine fluorescence, which can be used to indicate the intrathylakoid pH in intact chloroplasts, was reduced drastically even by low concentrations of NH4Cl. This suggests that the chloroplast phosphorylation potential is not in equilibrium with the proton gradient. In coupled chloroplasts, the intrathylakoid pH was lower in the light with nitrite than with oxaloacetate as electron acceptor. Electron flow was also more effectively controlled in chloroplasts illuminated with nitrite than with oxaloacetate. It is concluded that the intrathylakoid pH, not the phosphorylation potential, is a factor in the control of the rate of electron flow in intact chloroplasts.

Key words

Electron flow Intact chloroplasts Intrathylakoid pH Phosphorylation potential 

Abbreviations

CCCP

carbonylcyanide-m-chlorophenylhydrazone

OAA

oxalo-acetate

MES

2-(N-morpholino)-ethanesulfonic acid

HEPES

N-2-hyroxyethylpiperazine-N′-2-ethanesulfonic acid

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Copyright information

© Springer-Verlag 1979

Authors and Affiliations

  • Yoshichika Kobayashi
    • 1
  • Yorinao Inoue
    • 1
  • Kazuo Shibata
    • 1
  • Ulrich Heber
    • 2
  1. 1.Laboratory of Plant PhysiologyInstitute of Physical and Chemical Research (Rikagaku Kenkyusho)Wako-shi, SaitamaJapan
  2. 2.Botanisches Institut der Universität DüsseldorfDüsseldorfFederal Republic of Germany

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