Low pH induced structural reorganization in thylakoid membranes

• Published in: Biochimica et biophysica acta Vol. 1817; no. 8; pp. 1388 - 1391
• Main Authors: Jajoo, Anjana, Szabó, Milán, Zsiros, Ottó, Garab, Győző
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.08.2012
• Subjects: Acidic pH; acidification; Circular Dichroism; energy; Excitonic CD; fluorescence; fluorescence emission spectroscopy; Hydrogen-Ion Concentration; LHCII; peas; photosystem I; photosystem II; polymers; Psi-type CD; spinach; temperature; Thylakoid membranes; thylakoids; Thylakoids - chemistry; Psi-type CD; Acidic pH; Excitonic CD; LHCII; Circular dichroism; Thylakoid membranes
• ISSN: 0005-2728; 0006-3002; 1879-2650
• DOI: 10.1016/j.bbabio.2012.01.002

By using low temperature fluorescence spectroscopy, it has been shown that exposing chloroplast thylakoid membranes to acidic pH reversibly decreases the fluorescence of photosystem II while the fluorescence of photosystem I increases [P. Singh-Rawal et al. (2010) Evidence that pH can drive state transitions in isolated thylakoid membranes from spinach, Photochem Photobiol Sci, 9 830–837]. In order to shed light on the origin of these changes, we performed circular dichroism (CD) spectroscopy on freshly isolated pea thylakoid membranes. We show that the magnitude of the psi-type CD, which is associated with the presence of chirally ordered macroarrays of the chromophores in intact thylakoid membranes, decreases gradually and reversibly upon gradually lowering the pH of the medium from 7.5 to 4.5 (psi, polymer or salt induced). The same treatment, as shown on thylakoid membranes washed in hypotonic low salt medium possessing no psi-type bands, induces no discernible change in the excitonic CD. These data show that while no change in the pigment–pigment interactions and thus in the molecular organization of the bulk protein complexes can be held responsible for the observed changes in the fluorescence, acidification of the medium significantly alters the macro-organization of the complexes, hence providing an explanation for the pH-induced redistribution of the excitation energy between the two photosystems. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial. ► Thylakoid membrane reorganization in response to pH is shown by circular dichroism. ► Reversible reorganizations in the chiral macrodomains at low pH. ► Invariance of excitonic bands shows pH-insensitivity of the bulk protein complexes.