A non-invasive assay of the plastoquinone pool redox state based on the OJIP-transient.
The plastoquinone (PQ) pool of the photosynthetic electron transport chain becomes reduced under anaerobic conditions. Here, anaerobiosis was used as a tool to manipulate the PQ-pool redox state in darkness and to study the effects of the PQ-redox state on the Chl-a fluorescence (OJIP) kinetics in pea leaves (Pisum sativum L.). It is shown that the F(J) (fluorescence intensity at 3 ms) is linearly related to the area above the OJ-phase (first 3 ms) representing the reduction of the acceptor side of photosystem II (PSII) and F(J) is also linearly related to the area above the JI-phase (3-30 ms) that parallels the reduction of the PQ-pool. This means that F(J) depends on the availability of oxidized PQ-molecules bound to the Q(B)-site. The linear relationships between F(J) and the two areas indicate that F(J) is not sensitive to energy transfer between PSII-antennae (connectivity). It is further shown that a approximately 94% reduced PQ-pool is in equilibrium with a approximately 19% reduction of Q(A) (primary quinone acceptor of PSII). The non-linear relationship between the initial fluorescence value (F(20 micros)) and the area above the OJ-phase supports the idea that F(20 mus )is sensitive to connectivity. This is reinforced by the observation that this non-linearity can be overcome by transforming the F(20 micros)-values into [Q(A) (-)]-values. Based on the F(J)-value of the OJIP-transient, a simple method for the quantification of the redox state of the PQ-pool is proposed.
Tóth
Szilvia Z
SZ
Laboratory of Bioenergetics, University of Geneva, Chemin des Embrouchis 10, CH-1254, Jussy, Geneva, Switzerland.
Schansker
Gert
G
Strasser
Reto J
RJ
D000693:Anaerobiosis; D001681:Biological Assay / Q000379:methods*; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D005453:Fluorescence; D008027:Light; D010084:Oxidation-Reduction / Q000528:radiation effects; D018532:Pisum sativum / Q000378:metabolism* / Q000528:radiation effects; D010971:Plastoquinone / Q000378:metabolism*
D002734:Chlorophyll; D010971:Plastoquinone; D000077194:Chlorophyll A