title: Origin of chlorophyll fluorescence in plants at 55-75 degrees C.
abstract: The origin of heat-induced chlorophyll fluorescence rise that appears at about 55-60 degrees C during linear heating of leaves, chloroplasts or thylakoids (especially with a reduced content of grana thylakoids) was studied. This fluorescence rise was earlier attributed to photosystem I (PSI) emission. Our data show that the fluorescence rise originates from chlorophyll a (Chl a) molecules released from chlorophyll-containing protein complexes denaturing at 55-60 degrees C. This conclusion results mainly from Chl a fluorescence lifetime measurements with barley leaves of different Chl a content and absorption and emission spectra measurements with barley leaves preheated to selected temperatures. These data, supported by measurements of liposomes with different Chl a/lipid ratios, suggest that the released Chl a is dissolved in lipids of thylakoid membranes and that with increasing Chl a content in the lipid phase, the released Chl a tends to form low-fluorescing aggregates. This is probably the reason for the suppressed fluorescence rise at 55-60 degrees C and the decreasing fluorescence course at 60-75 degrees C, which are observable during linear heating of plant material with a high Chl a/lipid ratio (e.g. green leaves, grana thylakoids, isolated PSII particles).
authors.affiliation: Laboratory of Biophysics, Department of Experimental Physics, Palacký University, Olomouc, Czech Republic. ilik@risc.upol.cz
authors.forename: Petr
authors.initials: P
authors.lastname: Ilík
authors.forename: Roman
authors.initials: R
authors.lastname: Kouril
authors.forename: Jerzy
authors.initials: J
authors.lastname: Kruk
authors.forename: Beata
authors.initials: B
authors.lastname: Myśliwa-Kurdziel
authors.forename: Hana
authors.initials: H
authors.lastname: Popelková
authors.forename: Kazimierz
authors.initials: K
authors.lastname: Strzałka
authors.forename: Jan
authors.initials: J
authors.lastname: Naus
mesh_terms: D002734:Chlorophyll / Q000737:chemistry*; D005453:Fluorescence; D001467:Hordeum / Q000737:chemistry* / Q000378:metabolism*; D006358:Hot Temperature; D008055:Lipids / Q000032:analysis; D008081:Liposomes / Q000737:chemistry / Q000378:metabolism; D018515:Plant Leaves / Q000737:chemistry / Q000378:metabolism; D013052:Spectrometry, X-Ray Emission; D013054:Spectrophotometry, Atomic
chemical_list: D008055:Lipids; D008081:Liposomes; D002734:Chlorophyll