Photosystem fluorescence

Weis, E. Berry, J. A. (1987). Quantum efficiency of photosystem II in relation to energy -dependent quenching of chlorophyll fluorescence. Biochimica Bio-physica Acta, 894, 198-208. 

El Bissati, K., E. Delphin, N. Murata, A. Etienne, and D. Kirilovsky (2000). Photosystem II fluorescence quenching in the cyanobacterium Synechocystis PCC 6803 Involvement of two different mechanisms. Biochim Biophys Acta 1457(3) 229-242. 

Rakhimberdieva, M. G., I. N. Stadnichuk, I. V. Elanskaya, and N. V. Karapetyan (2004). Carotenoid-induced quenching of the phycobilisome fluorescence in photosystem II-deficient mutant of Synechocystis sp. FEBS Lett 574(1-3) 85-88. 

Principle Chlorophyll fluorescence is a sensitive and early indicator of damage to photosynthesis and to the physiology of the plant resulting from the effect of allelochemicals, which directly or indirectly affects the function of photosystem II (Bolhar-Nordenkemf et ah, 1989, Krause and Weiss 1991). This approach is convenient for a photosynthesis analysis in situ and in vivo and quick detection of otherwise invisible leaf damage. The photosynthetic plant efficiency was measured using the method of induced chlorophyll fluorescence kinetics of photosystem II [Fo, non-variable fluorescence Fm, maximum fluorescence Fv=Fm-Fo, variable fluorescence t /2, half the time required to reach maximum fluorescence from Fo to Fm and photosynthetic efficiency Fv/Fm]. 

I. Yamazaki, M. Mimuro, N. Tamai, T. Yamazaki and Y. Fujita, Picosecond time-resolved fluorescence spectra of photosystem I and II in Chlorella pyrenoidosa, FEES Lett. 179, 65-68 (1985) and references therein. 

FIGURE 6. Postulated excitation energy transfer sequence between the chlorophyll-proteins of photosystem I, with low temperature fluorescence emission peaks shown. This model has proven useful in predicting and interpreting the fluorescence emission spectra of barley mutants lacking one or more of the chlorophyll-proteins of photosystem I. Thus the viridisk23 mutant fluoresces at 720 nm and completely lacks LHCI, whereas the chlorophyll b-less mutant fluorescences at 730 nm, and LHCI can be detected by immunoblotting. 

Chlorophyll a fluorescence was measured with a dual-modulated fluorometer (Photosystem Instruments, Trtilek et al. 1997). Minimum (Fa) and maximum fluorescence (Fm) was recorded after dark adaptation (5 min at 4°C, sufficient to attain stabilization of the fluorescence signal for all light regimes). The maximum quantum yield of photosynthesis FvIFm was calculated as (Fm-F0)/Fm (Krause and Weis 1991). 

Kana R, Lazar D, Prasil O, Naus J (2002) Experimental and theoretical studies on the excess capacity of photosystem n. Photosynth Res 72 271-284 Krause GH, Weis E (1991) Chlorophyll fluorescence and photosynthesis the basics. Annu Rev Plant Physiol Plant Mol Biol 42 313-349... 

Fig. 4 Dynamics of in vivo chlorophyll fluorescence (Fo) and photosynthetic efficiency (Fv/Fm) of Phaeocystis globosa during viral infection as assessed by fluorometry. Open symbols represent uninfected cultures, while the filled symbols represent virally infected P. globosa. Maximum fluorescence (Fm) was obtained after addition of the photosystem II inhibitor DCMU (20 pM final concentration). Fv equals Fm-Fo. Data are expressed in relative units (r.u.)...

As we indicated in Chapter 4 (Section 4.3B), the emission of fluorescence means that the excitation caused by the absorption of light cannot be used for photochemistry. In particular, the excited trap of Photosystem II, Pg80, can become deexcited by photochemistry involving the electron transport chain (rate constant = /tph0tochem)> by fluorescence ( F), or by various other deexcitation processes (/fcothei. = sum of the rate constants for all such... 

Murata has discovered [97] that the addition of Mg to isolated thylakoids increases the fluorescence yield of PS II and its photochemical activity, decreasing at the same time the photochemical activity of PS I. These observations received further experimental support and widespread acceptance (see review by W.P. Williams [98]), and have been interpreted to indicate that the presence of Mg ion (and other cations as well) interrupts the transfer of excitation energy to PS I (which is not fluorescent at room temperature). So the concentration of cations in the medium seems to regulate the distribution of excitation energy between the two photosystems. The addition of cations was also shown to cause the stacking of thylakoids and the formation of grana [99] this process was found to be correlated to the fluorescence increase [100,101]. 

An important step towards the understanding of the regulation of excitation energy partition between the two photosystems has been the discovery of LHC phosphorylation by a thylakoid-bound protein kinase and its dephosphorylation by a phosphatase [124]. The kinase is activated when the plastoquinone pool is reduced, and inactivated when it becomes oxidized [125,126]. Phosphorylation of LHC leads to a decrease of PS II fluorescence of ca. 15-20%, and dephosphorylation to the opposite changes [127-129]. PS I photochemical activity is at the same time enhanced [130-133],... 

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