title: Heat-induced disassembly and degradation of chlorophyll-containing protein complexes in vivo.
abstract: Gradual heating of green leaves up to non-physiological temperatures is often used to estimate thermal stability of photosynthetic apparatus. However, a complete sequence of heat-induced disassembly and denaturation of chlorophyll-containing protein complexes (CPCs) has not been reported yet. In this work, we heated (1 degrees C x min(-1)) barley leaves to temperatures selected according to the changes in the chlorophyll fluorescence temperature curve (FTC) and we analyzed CPC stability by two-dimensional native Deriphat/SDS-PAGE. The first distinct change in both structure and function of photosystem II (PSII) appeared at 40-50 degrees C. PSII core (CCII) dimers began to dissociate monomers, which was accompanied by a decrease in PSII photochemistry and reflected in FTC as the first fluorescence increase. Further changes in CPCs appeared at 57-60 degrees C, when FTC increases to its second maximum. Photosystem I (PSI) cores (CCI) partially dissociated from light-harvesting complexes of PSI (LHCI) and formed aggregates. The rest of CCI-LHCI complexes, as well as the CCI aggregates, degraded to the PSI-A/B heterodimer in leaves heated to 70 degrees C. Heating to these temperatures led to a complete degradation of CCII components and corresponding loss of PSII photochemistry. Trimeric light-harvesting complexes of PSII (LHCII) markedly dissociated to monomers and denatured, as evidenced by a release of large amount of free chlorophylls. Between 70 and 80 degrees C, a complete degradation of LHCII occurred, leaving the PSI-A/B heterodimer as the only detectable CPC in the membrane. This most thermostable CPC disappeared after heating to 90 degrees C, which corresponded to a loss of PSI photochemistry.
authors.affiliation: Laboratory of Biophysics, Faculty of Science, Palacký University, Tr. Svobody 26, CZ-77146 Olomouc, Czech Republic.
authors.forename: Lenka
authors.initials: L
authors.lastname: Lípová
authors.forename: Pavel
authors.initials: P
authors.lastname: Krchnák
authors.forename: Josef
authors.initials: J
authors.lastname: Komenda
authors.forename: Petr
authors.initials: P
authors.lastname: Ilík
mesh_terms: D002734:Chlorophyll / Q000032:analysis; D001467:Hordeum / Q000378:metabolism; D006358:Hot Temperature; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry / Q000378:metabolism*; D008970:Molecular Weight; D010788:Photosynthesis; D010860:Pigments, Biological / Q000032:analysis; D018515:Plant Leaves / Q000737:chemistry / Q000378:metabolism / Q000528:radiation effects; D013816:Thermodynamics; D020524:Thylakoids / Q000737:chemistry
chemical_list: D045342:Light-Harvesting Protein Complexes; D010860:Pigments, Biological; D002734:Chlorophyll