Energy-dependent quenching of chlorophyll-a-fluorescence: the involvement of proton-calcium exchange at photosystem 2

Title:

Energy-dependent quenching of chlorophyll-a-fluorescence: the involvement of proton-calcium exchange at photosystem 2

Creator:

Krieger, A. and Weis, E.

Identifier:

https://cdk.lib.cas.cz/client/handle/uuid:d08d1ef0-f31f-4a24-866e-a1a3b27198cc
uuid:d08d1ef0-f31f-4a24-866e-a1a3b27198cc
urnnbn:urn:nbn:cz:aba007-000fan

Type:

model:internalpart and TEXT

Format:

print

Description:

The pH-dependent quenching of chlorophyll (Chl) fluorescence (the high energy quenching) was characterized by stationary Chl-a-fluorescence in the thylakoid membranes and photosystem (PS) 2 preparations. The variable part of fluorescence was quenched, when the pH in the thylakoid lumen decreased below 5.5, i.e., at high ApH. This quenching was caused by an inhibition of electron donation from the manganese cluster to the reaction centre of PS 2. The pH response of quenching suggested that a 1 H'''-transition with an apparent pK of 4.7 was involved. Parallel to quenching at low pH, a Ca^‘'‘-release was measured (1 Ca^'*' per 200 Chl). When the ApH relaxed and the pH on the lumen side increased again, fluorescence recovered provided Ca^'*' was present (Kd = 100 pM). Both the quenching at low pH and the reactivation at pH > 5.5 are light-dependent processes. In the presence of high concentration of extemal Ca^"^, fluorescence recovered even at low pH. Inhibition of the donor-side of PS 2 directly affected the acceptor-side of PS 2, as seen by a shift of the redox potential of Qa from -120 mV (pH 7.0) to +40 mV (pH 4.2). We propose that at high ApH (7) the water splitting side is inactivated by release of Ca from a high afflnity binding site, and (2) Qa is converted to a high-potential form. Excitatíon energy is then dissipated at the PS 2 reaction centres by a recombination reaction between donor and acceptor side. As a result, Qa (and the intersystem electron transport chain) remains oxidized, even in the excessive light.

Language:

Multiple languages

Rights:

http://creativecommons.org/licenses/by-nc-sa/4.0/
policy:public

Coverage:

89-98 and 107-116

Source:

Photosynthetica | 1992 Volume:27 | Number:1-2

Harvested from:

CDK

Metadata only:

false