Does residual bicarbonate account for residual Hill activity in formate-pretreated thylakoids?

Title:

Does residual bicarbonate account for residual Hill activity in formate-pretreated thylakoids?

Creator:

Moubarak-Milad, M. and Stemler, A.

Identifier:

https://cdk.lib.cas.cz/client/handle/uuid:0cbd3582-532d-4bbc-b5e3-af0ab4e6b04f
uuid:0cbd3582-532d-4bbc-b5e3-af0ab4e6b04f
urnnbn:urn:nbn:cz:aba007-000fph

Subject:

chlorophyll, irradiance, oxygen evolution, photosystem 2, and Spinacia oleracea

Type:

model:internalpart and TEXT

Format:

print

Description:

Membrane-bound bicarbonate is believed by some to act as an essential activator of photosystem 2 (PS2) electron transport. Formáte and other inhibitory monovalent anions act by removing bound-bicarbonate. This belief relies to a great extent on the observation that formáte (100 mM) pretreated thylakoids exhibit a non- proportionality between Hill activity (HAR) and chlorophyll (Chl) concentration when preirradiated with bright radiation in reaction mixture that contains only 5 mM formáte. The non-linearity was attributed to a supposed loosening of residual bicarbonate still present after formáte treatment and which would be more abundant at higher Chl concentrations. In repeating this experiment, we observed an increase in HAR at higher Chl concentrations in preirradiated, but also in non-preirradiated samples, the latter were simply left in the dark for 3 min before measurements were made. Therefore, preirradiation is not needed to restore some HAR in formáte pretreated samples; a 3 min wait in the electrode chamber at low formáte concentration is sufficient to partially relieve the formáte inhibition of PS2 activity. Moreover, HAR in samples preirradiated by weak radiation, or not preirradiated at all, was directly proportional to Chl concentration. We can attribute the increase in activity to a dissociation of bound formáte, not necessarily to the effect of residual bicarbonate. Non-linearity in HAR with Chl concentration was found only in high- irradiance pretreated samples. We can attribute this to a greater amount of photoinhibition occurring in the dilute samples, where the effective irradiance was greater. There is no need to postuláte the existence of residual bound bicarbonate to explain these results.

Language:

Multiple languages

Rights:

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

Coverage:

593-598 and 115-120

Source:

Photosynthetica | 1995 Volume:31 | Number:4

Harvested from:

CDK

Metadata only:

false