Role of the oxidized secondary acceptor QB of photosystem II in the delayed 'afterglow' chlorophyll luminescence.
Leaf discs of dark-adapted tobacco plants were excited by 2 flashes and kept in darkness at 20 degrees C for various time periods, then thermoluminescence emission was recorded without freezing the sample. The B band at 30 degrees C decreased with a half-time t1/2 approximately 1 min and the AG band at 45 degrees C with a t1/2 approximately 5 min. This corresponds to the decay kinetics of S2/3 in PS II centres in the state S2/3 QB - (B band) or S2/3 QB. Assuming that the 45 degrees C band is an 'afterglow' emission originating from those centres with an oxidized QB on which an electron is back-transferred from stroma reductants through a pathway induced by warming, the theoretical ratio of the B and AG band was compared to that measured experimentally. After 2 or 3 flashes producing mainly S3, the intensity of AG band encompassed several fold that of the B band, because recombining S3 recreated S2 QB AG-emitting centres. In order to confirm that the AG band is governed by the heat-induced activation of a dark QB-reducing pathway rather than by PS II charge recombination, the AG emission was characterized in triazine-resistant Chenopodium album weed biotypes. In these mutants where the QB pocket is altered, the B band is strongly downshifted to 18 degrees C, compared to 32 degrees C in the wild type, whereas the AG band is only downshifted by 3 or 4 degrees C, demonstrating that S2/3 QB - is not the limiting step of the AG emission.
Ducruet
Jean-Marc
JM
Service de Bioénergétique, DBJC, INRA/CEA Saclay, 91191 Gif-sur-Yvette, France. jean-marc.ducruet@cea.fr
Roman
Miruna
M
Ortega
Jose Maria
JM
Janda
Tibor
T
D027462:Chenopodium / Q000737:chemistry / Q000378:metabolism; D002734:Chlorophyll / Q000737:chemistry* / Q000378:metabolism*; D004579:Electron Transport; D049449:Luminescence; D010777:Photochemistry; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000378:metabolism; D013696:Temperature; D013997:Time Factors; D014026:Nicotiana / Q000737:chemistry / Q000378:metabolism*
D045332:Photosystem II Protein Complex; D002734:Chlorophyll