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.].
The influence of higher temperatures on the polypeptide composition of thylakoid membranes and pigment-protein complexes, as well as on some parameters of their functional activity, in both acclimated and non-acclimated young pea plants, was studied. Almost the whole set of polypeptides in thylakoid membranes as vvell as in T40 particles was preserved after heat treatment (5 h, 55 °C). During acclimation of the plants to high temperatures a reorganization of the photosynthetic apparatus took plače. In its thylakoids the oligomer/monomer ratio of the photosystem (PS) 2 light- harvesting antenna was more than 50 % higher compared to similar samples of the non-acclimated plants. After both the treatment of 5 h at 55 °C only (non-acclimated plants) and that with step-wise increasing temperatures (acclimated plants), the PSI activity was practically unchanged in all three variants, whereas the PS2 activity decreased more significantly in non-acclimated plants only.
Photon-induced absorbance changes at 830 nm (ΔA830) related to redox transformations of P700, primary electron donor of photosystem 1 (PS1), were examined in barley leaves treated with diuron and methyl viologen. In such leaves, only soluble reductants localized in chloroplast stroma could serve as electron donors for P700+. Δ A830 were induced by 1-min irradiation of leaves with "actinic light" (AL, 700±6 nm) of various irradiances. Two exponentially decaying components with half-times of 2.75 (fast component, relative magnitude of 62 % of ΔA830) and 11.90 s (slow one, 38 % of ΔA830) were distinguished in the kinetics of dark relaxation of ΔA830 after leaf irradiation with saturating AL. The components reflecting P700+ dark reduction in two units of PS1 differed in the rate of electron input from stromal reductants. The decline in AL irradiance reduced steady state δA830 magnitude, which was also accompanied by a decrease in the contribution of fast component to the overall P700+ dark reduction kinetics. The photon-response curves were obtained separately for rapidly and slowly decaying δA830. The values of half-saturating irradiance were 0.106 and 0.035 μmol m-2 s-1 for rapidly and slowly reduced PS1 units, respectively. The ratio of rate constants of P700+ dark reduction for rapidly and slowly reduced PS1 units was 1.4 times higher than the ratio of their half-saturating irradiances thus indicating higher relative antenna size in rapidly reduced PS1 units. The latter finding, taken together with higher relative amount of P700, favours the view that rapidly and slowly reduced PS1 units reflect P700+ reduction by stromal reductants in spatially separated PS1α and PS1β complexes. and E. A. Egorova, N. G. Bukhov.
The aim of our study was to answer whether any positive correlation exists between K+ uptake and salt tolerance in wheat. We carried out a sand-culture experiment with salt-tolerant, DK961 (ST), and salt-sensitive, JN17 (SS), wheat cultivars, where photosynthesis, the K+/Na+ ratio, growth, and the biomass yield were examined. The seeds were exposed for four weeks to six NaCl concentrations (50, 100, 150, 200, 250, and 300 mM), which were embodied in the Hoagland solution. Salinity-induced decrease of K+ or increase in the Na+ content was much smaller in ST than that in SS. The reductions in the light-saturated photosynthetic rate (P Nmax) and chlorophyll content caused by salinity were smaller in the ST compared to SS. Stomatal conductance decreased in both cultivars under saline conditions; nevertheless, it was lower in SS than in ST. The antioxidative capacity was higher in ST than that in SS under saline conditions. Significant positive correlations were observed in both cultivars between K+ contents and P Nmax/biomass yields. We suggest that higher-affinity K+ uptake might play a key role in higher salt tolerance and it might be a reliable indicator for breeding new species of salt-tolerant wheat., D. Cheng, G. Wu, Y. Zheng., and Obsahuje seznam literatury
Using fluorescence methods, it was shown that the energy transfer from flavin to protochlorophyilide (PChlide) 655/650 and to the products of its photoconversion (chlorophyllide) couid be observed up to the completion of the Shibata shift. The changes in fluorescence spectra of NADPH and flavins, accompanying the PChlide 655/650 photoreduction at 77 K, allow to assume the participation of NADPH and flavins in the primary photoreactions of chlorophyllide formation.
We demonstrate the feasibility of assaying and predicting post-harvest damage in lemons by monitoring chlorophyll (Chl) fluorescence. Fruit quality was assayed using a commercial instrument that determines photosynthetic performance by imaging Chl fluorescence parameters under different irradiances. Images of Chl fluorescence from individual lemons reveal that photosynthesis is active throughout the post-harvest ripening process. Because photosynthesis is highly sensitive to biotic and abiotic stress, variations in Chl fluorescence parameters over the surface of a lemon fruit can be used to predict areas that will eventually exhibit visible damage. The technique is able to distinguish between mould-infected areas that eventually spread over the surface of the fruit, and damaged areas that do not increase in size during ripening. This study demonstrates the potential for using rapid imaging of Chl fluorescence in post-harvest fruit to develop an automated device that can identify and remove poor quality fruit long before visible damage appears. and L. Nedbal ... [et al.].