ARTICLE

PROTONATION AND CHLOROPLAST MEMBRANE STRUCTURE

Satoru Murakami ¹ and Lester Packer ¹

¹ From the Department of Physiology-Anatomy, University of California, Berkeley, California 94720

Light changes the structure of chloroplasts. This effect was investigated by high resolution electron microscopy, photometric methods, and chemical modification. (a) A reversible contraction of chloroplast membrane occurs upon illumination, dark titration with H⁺, or increasing osmolarity. These gross structural changes arise from a flattening of the thylakoids, with a corresponding decrease in the spacing between membranes. Microdensitometry showed that illumination or dark addition of H⁺ resulted in a 13–23% decrease in membrane thickness. Osmotically contracted chloroplasts do not show this effect. (b) Rapid glutaraldehyde fixation during actual experiments revealed that transmission changes are closely correlated with the spacing changes and therefore reflect an osmotic mechanism, whereas the light scattering changes have kinetics most similar to changes in membrane thickness or conformation. (c) Kinetic analysis of light scattering and transmission changes with the changes in fluorescence of anilinonaphthalene sulfonic acid bound to membranes revealed that fluorescence preceded light scattering or transmission changes. (d) It is concluded that the temporal sequence of events following illumination probably are protonation, changes in the environment within the membrane, change in membrane thickness, change in internal osmolarity accompanying ion movements with consequent collapse and flattening of thylakoid, change in the gross morphology of the inner chloroplast membrane system, and change in the gross morphology of whole chloroplasts.

CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?

This article has been cited by other articles:

• Pfeiffer, S., Krupinska, K. (2005). New Insights in Thylakoid Membrane Organization. Plant Cell Physiol 46: 1443-1451 [Abstract] [Full Text]  
• Cruz, J. A., Salbilla, B. A., Kanazawa, A., Kramer, D. M. (2001). Inhibition of Plastocyanin to P700+ Electron Transfer in Chlamydomonas reinhardtii by Hyperosmotic Stress. Plant Physiol. 127: 1167-1179 [Abstract] [Full Text]  

Home | Help | Feedback | Subscriptions | Archive | Search | Table of Contents