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Heterogeneity of photosystem II reaction centers as influenced by heat treatment of barley leaves
Author(s) -
Bukhov Nikolai G.,
Carpentier Robert
Publication year - 2000
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1034/j.1399-3054.2000.110219.x
Subject(s) - photosystem ii , photochemistry , electron acceptor , population , chemistry , dcmu , electron transfer , electron transport chain , chlorophyll fluorescence , photosynthetic reaction centre , oxygen , photosystem , photosynthesis , acceptor , plastoquinone , chloroplast , photosystem i , thylakoid , biochemistry , organic chemistry , demography , physics , sociology , gene , condensed matter physics
Three functionally distinct populations of PSII reaction centers differing in the ability to keep the primary acceptors in a reduced state and to transfer electrons to PSI were estimated using chlorophyll fluorescence measurements in primary barley leaves exposed to elevated temperatures in the range of 37–51°C. The capacity of the PSII reaction centers to perform at least one light‐induced charge separation was not affected by a 5‐min heat treatment at temperatures up to 51°C. The first population containing Q B ‐non‐reducing centers corresponded to 15–20% of the total PSII activity up to 45°C. In a second population, PSII reaction centers maintained Q A reduction under light in the presence of oxygen, but not in the presence of a strong artificial PSI electron acceptor, methyl viologen. In a third population that gradually increases from zero at 37°C to about 60% at 45°C, the PSII centers were not able to keep Q A in the reduced state even in the presence of oxygen as the sole electron acceptor. Three electron transport pathways, the pseudocyclic one involving both PSII and PSI, the NAD(P)H‐dependent pathway mediated by PSI alone after the loss of activity in some PSII centers, and the PSI‐driven ferredoxin‐dependent route enhanced by weakly efficient PSII centers that are able to provide only catalytic amounts of electrons, are suggested to create a proton gradient in chloroplasts of heat‐stressed leaves thus protecting PSII reaction centers from photodamage.