2007) Several studies, using imaging to study Chl a fluorescence

2007). Several studies, using imaging to study Chl a fluorescence parameters under various conditions (high/low ambient CO2 concentration, high/low light intensity, etc.), have yielded information on the relationship between MK-2206 supplier leaf structure and organization on the one hand and the response to stress conditions on the

other (Baker 2008; Roháček et al. 2008; Guidi and Degl’Innocenti 2011; Gorbe and Calatayud 2012). Serôdio et al. (2013) have introduced, a new application of fluorescence-imaging systems, which allows the rapid generation of light-response curves (see Question 18) simultaneously illuminating replicates of samples using spatially separated beams of Cell Cycle inhibitor actinic light of different intensities. Question 15. What kind of information can be obtained using the quenching analysis (see Question 2)? In leaves exposed to a certain irradiance, the fluorescence intensity is affected by changes both in the redox state of the ETC (particularly the redox state of Q A) and in the fluorescence yield due to light-induced changes in the properties of the PSII antenna. A method called the quenching analysis was developed to separate these two types of process. In most cases, the quenching analysis is used to describe the steady state, i.e., the stable photosynthetic

activity, which is usually reached after approximately 5–10 min of illumination at a chosen actinic light intensity. A protocol was developed (Schreiber et al. 1986; Fig. 4) based among others on the work of Bradbury and Baker Pinometostat clinical trial (1981) in which the measurements are initiated by switching on the measuring light to determine the F O value of a dark-adapted sample. A saturating light pulse is then applied to determine Thymidine kinase the F M. The measurement is continued switching on an actinic light source to induce

photosynthesis, until the fluorescence emission stabilizes at a level called F S. The F M′ is then determined by applying another strong pulse of light followed some time later (e.g., 10 s) by turning off the actinic light. Turning off, the actinic light will cause a quick, partial, re-oxidation of the photosynthetic ETC. Within the first 100 ms of darkness, the PQ-pool will be largely re-oxidized by forward electron transport toward PC+ and P700+, and a value close to F O′ can be measured. The F O′ level subsequently increases again due to non-photochemical reduction of the PQ-pool by NADPH and possibly Fdred (Mano et al. 1995; Gotoh et al. 2010; Guidi and Degl’Innocenti 2012). This so-called “F O′ rise” can be almost completely suppressed by a short pulse of FR light (e.g., of 1 s duration) following the turning off of the actinic light. The increase of the fluorescence intensity from F S to F M′ is related to a change in the redox state of the ETC, whereas the difference between F M′ and the dark-adapted F M is then a measure of the fluorescence yield change, which in the case of qE is associated with increased heat dissipation.

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