Thermostability and photostability of photosystem II in leaves of the Chlorina-f2 barley mutant deficient in light-harvesting chlorophyll a/b protein complexes.

摘要

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 atabout 35鳦 and 38.5鳦 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-kDa 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-f2and 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 inthe wild type. This difference was not observed in anaerobiosis or in the presence of diuron. The acceptor side of PSII was only slightly affected by the mutation and/or the aforementioned stress conditions. It is concluded that LHCII stabilize the PSIIcomplexes and maintain the water-oxidizing system in a functional state under varying environmental conditions.