High-Temperature Induced Chlorophyll Fluorescence Rise in Plants at 40-50 degrees C: Experimental and Theoretical Approach

• Published in: Photosynthesis research Vol. 81; no. 1; pp. 49 - 66
• Main Authors: Kouril, Roman, Lazár, Dusan, Ilík, Petr, Skotnica, Jirí, Krchnák, Pavel, Naus, Jan
• Format: Journal Article
• Language: English
• Published: Netherlands 2004
• ISSN: 1573-5079
• DOI: 10.1023/B:PRES.0000028391.70533.eb

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.