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PLANT PHYSIOLOGY , Vol 113, Issue 3 913-923, Copyright © 1997 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
Thermostability and Photostability of Photosystem II in Leaves of the Chlorina-f2 Barley Mutant Deficient in Light-Harvesting Chlorophyll a/b Protein Complexes
M. Havaux and F. Tardy
Departement d'Ecophysiologie Vegetale et de Microbiologie, Commissariat a l'Energie Atomique, Centre d'Etudes de Cadarache, F-13108 Saint-Paul-Iez-Durance, France
The chlorophyll-b-less chlorina-f2 barley mutant is deficient in the major
as well as some minor light-harvesting chlorophyll-protein complexes of
photosystem II (LHCII). Although the LHCII deficiency had relatively minor
repercussions on the leaf photosynthetic performances, the responses of
photosystem II (PSII) to elevated temperatures and to bright light were
markedly modified. The chlorina-f2 mutation noticeably reduced the
thermostability of PSII, with thermal denaturation of PSII starting at
about 35[deg]C and 38.5[deg]C in chlorina-f2 and in the wild type,
respectively. The increased susceptibility of PSII to heat stress in
chlorina-f2 leaves was due to the weakness of its electron donor side, with
moderate heat stress causing detachment of the 33-kD extrinsic PSII protein
from the oxygen-evolving complex. Prolonged dark adaptation of chlorina-f2
leaves was also observed to inhibit the PSII donor side. However, weak
illumination slowly reversed the dark-induced inhibition of PSII in
chlorina-f2 and cancelled the difference in PSII thermostability observed
between chlorina-f2 and wild-type leaves. The mutant was more sensitive to
photoinhibition than the wild type, with strong light stress impairing the
PSII donor side in chlorina-f2 but not in the wild type. This difference
was not observed in anaerobiosis or in the presence of
3-(3,4-dichlorophenyl)- 1,1-dimethylurea, diuron. The acceptor side of PSII
was only slightly affected by the mutation and/or the aforementioned stress
conditions. Taken together, our results indicate that LHCII stabilize the
PSII complexes and maintain the water-oxidizing system in a functional
state under varying environmental conditions.
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