title: High-Temperature Induced Chlorophyll Fluorescence Rise in Plants at 40-50 degrees C: Experimental and Theoretical Approach.
abstract: We studied the temperature dependence of chlorophyll fluorescence intensity in barley leaves under weak and actinic light excitation during linear heating from room temperature to 50 degrees C. The heat-induced fluorescence rise usually appearing at around 40-50 degrees C under weak light excitation was also found in leaves treated with 3-(3',4'-dichlorophenyl)-1,1-dimethylurea (DCMU) or hydroxylamine (NH(2)OH). However, simultaneous treatment with both these compounds caused a disappearance of the fluorescence rise. We have suggested that the mechanism of the heat-induced fluorescence rise in DCMU-treated leaves is different than that in untreated or NH(2)OH-treated leaves. In DCMU-treated leaves, the heat-induced fluorescence rise reflects an accumulation of Q(A) (-) even under weak light excitation due to the thermal inhibition of the S(2)Q(A) (-) recombination as was further documented by a decrease in the intensity of the thermoluminescence Q band. Mathematical model simulating this experimental data also supports our interpretation. In the case of DCMU-untreated leaves, our model simulations suggest that the heat-induced fluorescence rise is caused by both the light-induced reduction of Q(A) and enhanced back electron transfer from Q(B) to Q(A). The simulations also revealed the importance of other processes occurring during the heat-induced fluorescence rise, which are discussed with respect to experimental data.
authors.affiliation: Laboratory of Biophysics, Faculty of Science, Palacký University, tr, Svobody 26, 771 46, Olomouc, Czech Republic.
authors.forename: Roman
authors.initials: R
authors.lastname: Kouril
authors.forename: Dusan
authors.initials: D
authors.lastname: Lazár
authors.forename: Petr
authors.initials: P
authors.lastname: Ilík
authors.forename: Jirí
authors.initials: J
authors.lastname: Skotnica
authors.forename: Pavel
authors.initials: P
authors.lastname: Krchnák
authors.forename: Jan
authors.initials: J
authors.lastname: Naus