The decay of chlorophyll (Chl) fluorescence of etiochloroplasts isolated in various stage of greening of cucumber cotyledons was analysed in order to get structural information on a photosynthetic apparatus. Two model decays, multiexponential and stretched exponential, were applied in the analysis. The quality of fit in these two models was different in various stages of chloroplast greening. The two-exponent model did not provide a good fit at early greening stages. To improve the fit it was necessary to introduce an additional third component which became very low at later stages. However, chloroplasts in the early stage of greening could also be described by a stretched exponential with parameters indicating rather planar (two-dimensional) arrangement of donor and acceptor molecules. The chloroplasts treated by DCMU and/or photooxidized by strong irradiance exhibit a similar character of fractal decay as untreated samples but in the multiexponential model the exact values of lifetimes and amplitudes of components vary. This suggests that the structure of investigated system does not dramatically change as a result of these two types of treatment. and A. Kowalczyk, A. Waloszek, D. Frąckowiak.
The polarized absorption, photoacoustic, fluorescence emission, and fluorescence excitation spectra of whole cells of cyanobacteria Synechocystis sp. embedded in a polymer film were measured. The bacteria cells, as it follows from anisotropy of absorption and fluorescence spectra, were even in a non-stretched polyvinyl alcohol film oriented to a certain extent. The measurements were done for such film in order to avoid the deformation of cyanobacteria shapes. Part of the samples was bleached by irradiation with strong polarized radiation with electric vector parallel to the orientation axis of cells. The anisotropy of photoacoustic spectra was higher than that of absorption spectra and it was stronger changed by the irradiation. Polarized fluorescence was excited in four wavelength regions characterised by different contribution to absorption from various bacteria pigments. The shapes of emission spectra were different depending on wavelength of excitation, polarization of radiation, and previous irradiation of the sample. The fluorescence spectra were analysed on Gaussian components belonging to various forms of pigments from photosystems (PS) 1 and 2. The results inform about excitation energy transfer between pools of pigments, differently oriented in the cells. Energy of photons absorbed by phycobilisomes was transferred predominantly to the chlorophyll of PS2, whereas photons absorbed by carotenoids to chlorophylls of PS1. and J. Goc ... [et al.].
The review summarizes results concerning photosynthetic systems with chlorophylls and carotenoids obtained by means of spectral methods such as polarized radiation, photoacoustic spectroscopy, delayed luminescence, thermal deactivation, and leading to construction of model systems. and D. Frąckowiak, B. Smyk.
In aqueous solutions of chlorophyll (Chl) a with synthesized polypeptides, at high ratios of Chl to polypeptides (about 75-150 µM to 500 µM) clusters of polypeptides and pigment molecules were formed. The main absorption maxima of more than one formed cluster were located at about 500 nm (Soret band) and in the region of 720-806 nm (red band). The formation of these clusters was fairly slow (some hours) at room temperature and even slower at 4 °C. The rate of cluster formation increased with the increase in Chl concentration. The addition of the even low amount of reaction centres (RCs), separated from the purple bacteria Rhodobacter sphaeroides, to the sample of Chl with polypeptides caused a very strong decrease in the efficiency of cluster formation, and a change in concentration ratios of various pigment-polypeptide aggregates. It was probably a competition between the interaction of Chl with polypeptides and with the RCs. The yield of thermal deactivation of the clusters was high, much higher than that for the RCs alone and it was different for various types of cluster. The clusters absorbing at 725-750 nm were fluorescent with maximum of emission at about 770 nm, whereas clusters absorbing at about 800 nm were nonfluorescent. and H. Enomoto ... [et al.].
The character of interaction between carotenoids (Cars) and chlorophylls (Chls) in thylakoids isolated from cucumber cotyledons at three stages of greening (3, 6, and 24 h of irradiation with 120 µmol m-2 s-1) was studied. The shapes of the steady state photoacoustic spectra were changed with the change in time of greening and with the frequency of radiation modulation. The shapes show that changes not only in the contents of various pigments but also in pigment interactions with surrounding occur and that processes of thermal deactivation characterised by different kinetics take place. Slow processes of thermal deactivation are in most cases due to deactivation of triplet states. Long living triplet states are very often engaged in photochemical reactions that can destroy the tissue. Analysis of the time-resolved photothermal spectra shows that at later stage of greening, the chlorophyll (Chl) molecules are better shielded against photo-destruction because Cars more efficiently quench their triplet states. The yield of formation of the pigment triplet states measured by the time resolved photothermal method, always at the same energy absorbed by pigment mixture, declined during sample greening. The decay time of the slow component of pigment thermal deactivation, due predominantly to deactivation of the triplet state of Chl, decreases with the increase of time of greening from 6.2 µs for the 3-h sample to 1.5 µs for the 24 h sample. The energy taken by Cars from Chls is dissipated into heat, therefore the steady state and quick thermal deactivation values increased during the greening process. The Cars/Chls ratio in the thylakoids decreased during greening approximately 2 fold. Hence at a later phase of greening the Cars can quench the triplet states of Chls more efficiently than at an earlier phase of greening. and A. Waloszek ... [et al.].
Photoacoustic spectra (PAS) were obtained for the cyanobacterium Synechococcus (Anacystis nidulans) cells embedded in isotropic and stretched polyvinyl alcohol films. The polarized radiation with the electric vector changing in 30° intervals with respect to given direction in a sample plane was used. Two cyanobacterium strains, one with very low biliprotein content, second with normal amount of biliproteins were investigated. The polarized absorption and fluorescence spectra were also measured. Conclusions were drawn about the thermal deactivation occurring in differently oriented pools of chromophores and about mutual orientation of their transition moments. Thermal deactivation in carotenoids (Cars) of both strains was different. The ratio of Car thermal deactivation to the thermal deactivation of chlorophyll (Chl) was higher in cyanobacteria with lower content of biliproteins than in the strain with normal amount of these complexes. Hence biliproteins can play the role in excitation energy transfer from Cars to Chls. For complex biological samples, polarized PAS can be a more sensitive method to investigate the directions of the absorption transition moments than the widely used polarized absorption spectra. and A. Planner ... [et al.].