Thylakoids from pea seedlings grown under intermittent light: biochemical and flash-spectrophotometric properties.
Thylakoid membranes were isolated from pea seedlings grown under intermittent light (2-min light/118-min dark cycles). These preparations differed from controls (thylakoids from plants grown under 16-h light/8-h dark cycles) in the following respects: 15 times smaller chlorophyll/protein ratio, 10 times greater chlorophyll a/b ratio, absence of light-harvesting chlorophyll a/b binding proteins, and 2-3-fold greater ratio of photosystem II over photosystem I. In addition we found the following: (1) Electrogenic electron transfer around cytochrome b6/f under flashing light was greatly enhanced, probably as a consequence of the greater photosystem II/photosystem I ratio. (2) The rate of proton uptake from the medium at the acceptor side of photosystem II was enhanced, probably by unshielding of the quinone binding domain. (3) The N,N'-dicyclohexylcarbodiimide sensitivity of the proton-pumping activity of photosystem II was absent, which was consistent with the attribution of a N,N'-dicyclohexylcarbodiimide-induced protonic short circuit to chlorophyll a/b binding proteins. (4) The sensitivity of oxygen evolution under continuous light to variations of pH or the concentration of Ca2+ was altered. Chlorophyll a/b binding proteins serve as light-harvesting antennas. We found in addition that they modulated the activity of water oxidation and, in particular, the proteolytic reactions around photosystem II.
Jahns
P
P
Biophysik, Fachbereich Biologie/Chemie, Universität Osnabrück, Germany.
Junge
W
W
D002458:Cell Fractionation; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D007887:Fabaceae / Q000254:growth & development / Q000378:metabolism* / Q000528:radiation effects; D006863:Hydrogen-Ion Concentration; D007425:Intracellular Membranes / Q000378:metabolism* / Q000502:physiology / Q000648:ultrastructure; D007700:Kinetics; D008027:Light; D045342:Light-Harvesting Protein Complexes; D008564:Membrane Potentials; D015388:Organelles / Q000378:metabolism* / Q000648:ultrastructure; D010100:Oxygen / Q000378:metabolism; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000302:isolation & purification / Q000378:metabolism; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D010946:Plants, Medicinal; D013053:Spectrophotometry
D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D002734:Chlorophyll; C037184:chlorophyll b; D010100:Oxygen; D000077194:Chlorophyll A