Photophysical processes of energy conversion in thylakoid membranes of <Emphasis Type="Italic">Chlamydomonas reinhardtii</Emphasis> mutants D1-R323H,D1-R323D,and D1-R323L |
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Authors: | G P Kukarskikh V E Zagidullin T K Antal T E Krendeleva V Z Paschenko |
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Institution: | 1.Faculty of Biology,Moscow Lomonosov State University,Moscow,Russia |
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Abstract: | Chlamydomonas reinhardtii mutants D1-R323H, D1-R323D, and D1-R323L showed elevated chlorophyll fluorescence yields, which increased with decline of
oxygen evolving capacity. The extra step K ascribed to the disturbance of electron transport at the donor side of PS II was
observed in OJIP kinetics measured in mutants with a PEA fluorometer. Fluorescence decay kinetics were recorded and analyzed
in a pseudo-wild type (pWt) and in mutants of C. reinhardtii with a Becker and Hickl single photon counting system in pico- to nanosecond time range. The kinetics curves were fitted
by three exponentials. The first one (rapid, with lifetime about 300 ps) reflects energy migration from antenna complex to
the reaction center (RC) of photosystem II (PS II); the second component (600–700 ps) has been assigned to an electron transfer
from P680 to QA, while the third one (slow, 3 ns) assumingly originates from charge recombination in the radical pair P680+• Pheo−•] and/or from antenna complexes energetically disconnected from RC II. Mutants showed reduced contribution of the first component,
whereas the yield of the second component increased due to slowing down of the electron transport to QA. The mutant D1-R323L with completely inactive oxygen evolving complex did not reveal rapid component at all, while its kinetics
was approximated by two slow components with lifetimes of about 2 and 3 ns. These may be due to two reasons: a) disconnection
between antennae complexes and RC II, and b) recombination in a radical pair P680+• Pheo−•] under restricted electron transport to QA. The data obtained suggest that disturbance of oxygen evolving function in mutants may induce an upshift of the midpoint
redox potential of QA/QA− couple causing limitation of electron transport at the acceptor side of PS II. |
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