Planta

, Volume 205, Issue 2, pp 297–304

Light-independent degradation of stromal proteins in intact chloroplasts isolated from Pisum sativum L. leaves: requirement for divalent cations

  • Samuel Roulin
  • Urs Feller
Article

DOI: 10.1007/s004250050324

Cite this article as:
Roulin, S. & Feller, U. Planta (1998) 205: 297. doi:10.1007/s004250050324

Abstract.

Intact chloroplasts were isolated from mature pea (Pisum sativum L.) leaves in order to study the degradation of several stromal proteins in organello. Changes in the abundances of ribulose-1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39), phosphoribulokinase (EC 2.7.1.19), glutamine synthetase (EC 6.3.1.2) and ferredoxin-dependent glutamine:α-ketoglutarate aminotransferase (glutamate synthase; EC 1.4.7.1) were detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by Coomassie-staining of the gels or immunoblotting using specific antibodies for the different enzymes. Degradation of several stromal proteins was strongly stimulated when intact chloroplasts were incubated in the light in the presence of dithiothreitol. Since free radicals may artificially accumulate in the chloroplast under such conditions and interfere with the stability of stromal proteins, the general relevance of these processes remains questionable. In the absence of light, proteolysis proceeded slowly in isolated chloroplasts and was not stimulated by dithiothreitol. Inhibition by ethylenediaminetetraacetic acid (EDTA), 1,10-phenanthroline or excess zinc ions as well as the requirement for divalent cations suggested that a zinc-containing metalloprotease participated in this process. Furthermore, light-independent degradation of ribulose-1,5-bisphosphate carboxylase/oxygenase and phosphoribulokinase was enhanced in chloroplasts isolated from leaves in which senescence was accelerated by nitrogen starvation. Our results indicate that light-independent stromal protein degradation in intact chloroplasts may be analogous to proteolysis that occurs in intact leaves during senescence.

Key words: Chloroplast Nitrogen remobilization Pisum Proteolysis Senescence Stromal enzymes 

Copyright information

© Springer-Verlag Berlin Heidelberg 1998

Authors and Affiliations

  • Samuel Roulin
    • 1
  • Urs Feller
    • 1
  1. 1.Institute of Plant Physiology, University of Bern, Altenbergrain 21, CH-3013 Bern, SwitzerlandCH

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