Assessment of the effects of methylmercury and copper ions on primary processes of photosynthesis in green microalga Chlamydomonas moewusii by analysis of the kinetic curves of variable chlorophyll fluorescence

The effect of methylmercury and copper ions on the kinetics of light induction and dark relaxation of the variable fluorescence of chlorophyll a has been studied on cultures of unicellular alga Chlamydomonas moewusii. Methylmercury was effective at much lower levels. The toxicants at concentrations that did not decrease the photochemical activity of PS II (F _v/F _m) did affect the electron transport on the acceptor side of PS II, nonphotochemical quenching of excitation in the antenna, and reoxidation of the quinone pool. Our results indicate that this approach can be used for detecting the changes in plant cells at the early stages of toxicant action.     

Optimization of Maintenance Conditions for Some Microforms of Red Algae in Collections

The effects of light and temperature conditions on the maintenance of some red microalgae (order Porphyridiales) in collections were studied. Periodical subculturing on solid and liquid media was used for maintenance. Halophilic species P. aeruginosa, P. cruentum, and P. sordidum were lost in 2.5 months if kept in darkness. The viability of algae in the dim light slightly declined in 4–5 months and was species-dependent. The results were compared with earlier obtained data on mesophilic Chlorococcales. For the green algae, darkness proved to be the optimal condition, while their viability markedly decreased at light. It was suggested that this discrepancy was caused by the presence of phycobiliproteins in the cells of red algae. Dim light conditions are optimal for the synthesis of phycobiliproteins, which are rapidly destroyed in darkness, thus leading to cell death.     

Two types of PS II centres as manifested by light saturation of delayed fluorescence from DCMU-treated chloroplasts

Intensity of 2 s delayed fluorescence (DF) as a function of steady-state actinic light intensity was investigated in pea chloroplasts in the presence of 10 M DCMU. The light saturation curve of DF was approximated by a sum of two hyperbolic components which differ by an order of magnitude in the half-saturating incident light intensity. The relative contribution of the amplitudes of the components was practically independent of cation (Na⁺ and Mg²⁺) concentration and a short-term heating of the chloroplasts at 45°C. The component saturating at low incident light intensity was selectively suppressed by 100 M DCMU or by 1 mol g^-1 Chl oleic acid. DF intensity following excitation by a single saturating 15 s flash was equal to the intensity of the component saturating at a low incident light intensity. Upon flash excitation, the maximum steady-state DF level was found to be attained only after a series of saturating flashes. It is concluded that the two components of the DF light saturation curves are related to PS II centres heterogeneity in quantum yield of stabilization of the reduced primary quinone acceptor.Abbreviations DF Delayed fluorescence - L₁- and L₂-components DF components saturating at low and high incident light intensity, respectively - I incident light intensity - L DF intensity - P₆₈₀ reaction centre chlorophyll of PS II - Q_A and Q_B primary and secondary quinone acceptors of PS II, respectively     

Ultrastructural organization of chloroplast membranes in mutants of Pisum sativum L. with impaired activity in the photosystems

The ultrastructural organization and the photosynthesis reactions of chloroplast membranes were studied in three lethal mutants of Pisum sativum, Chl-1, Chl-19 and Chl-5, all lacking the capacity to evolve oxygen. The rates of 2,6-dichloroindophenol reduction, delayed fluorescence and electron-spin-resonance signal 1 indicate that Chl-1 and Chl-19 have an impaired activity in photosystem II (PS II), while in Chl-5 the electron transport is blocked between PS I and the reactions of CO₂ fixation. Ultrathin sectioning demonstrates the presence of giant grana in the chloroplasts of Chl-1 and Chl-19, while the chloroplast structure of the Chl-5 is very similar to that of the wild-type. The grana of the Chl-19 mutant contain large multilamellar regions of tightly packed membranes. When the chloroplast membranes were studied by freeze-fracture, the exoplasmic and protoplasmic fracture faces (EF and PF, respectively) in both stacked and unstacked membranes were found to show large differences in particle concentrations and relative population area (per m²), and also in particle size distribution, between all mutant chloroplast membranes and the wild-type. A close correlation between increasing k_mt (ratio of particle concentrations on PF/EF) and PS II activity was observed. The differences in particle concentrations on both fracture faces in different regions of the intact chloroplast membranes of the wild-type are the consequence of a rearrangement of existing membrane components by lateral particle movements since quantitative measurements demonstrate almost complete conservation of intramembrane particles in number and size during the stacking of stroma thylakoid membranes. The results indicating particle movements strongly support the concept that the chloroplast membranes have a highly dynamic structure.Abbreviations DPIP 2,6-dichloroindophenol - EF and PF exoplasmic and protoplasmic fracture faces, respectively - PS I and PS II photosystems I and II, respectively     

Determination of the Promising Microalgal Strain for Bioremediation of the Aquaculture Wastewater

Microbiology - Applicability of three strains of green microalgae (Chlorella vulgaris SP BB-2, Parachlorella kessleri, and Chlamydomonas reinhardtii Dangeard СС-124) for...     

Real-time enzyme dynamics illustrated with fluorescence spectroscopy of p-hydroxybenzoate hydroxylase

We have used the flavoenzyme p-hydroxybenzoate hydroxylase (PHBH) to illustrate that a strongly fluorescent donor label can communicate with the flavin via single-pair F?rster resonance energy transfer (spFRET). The accessible Cys-116 of PHBH was labeled with two different fluorescent maleimides with full preservation of enzymatic activity. One of these labels shows overlap between its fluorescence spectrum and the absorption spectrum of the FAD prosthetic group in the oxidized state, while the other fluorescent probe does not have this spectral overlap. The spectral overlap strongly diminished when the flavin becomes reduced during catalysis. The donor fluorescence properties can then be used as a sensitive antenna for the flavin redox state. Time-resolved fluorescence experiments on ensembles of labeled PHBH molecules were carried out in the absence and presence of enzymatic turnover. Distinct changes in fluorescence decays of spFRET-active PHBH can be observed when the enzyme is performing catalysis using both substrates p-hydroxybenzoate and NADPH. Single-molecule fluorescence correlation spectroscopy on spFRET-active PHBH showed the presence of a relaxation process (relaxation time of 23 micros) that is related to catalysis. In addition, in both labeled PHBH preparations the number of enzyme molecules reversibly increased during enzymatic turnover indicating that the dimer-monomer equilibrium is affected.     

Effect of pH and substitution of H2O for D2O on oxygen liberation by chloroplasts

The rate of dark relaxation of the oxygen evolving system in chloroplasts is shown to depend on the value of the surface charge of some chloroplast membrane component having protein nature and isoelectric point at pH 6.0. The substitution of H2O for D2O leads to isoelectric point shift of this protein.     

Cryptomonad alga Rhodomonas sp. (Cryptophyta,Pyrenomonadaceae) bloom in the redox zone of the basins separating from the White Sea

Bloom of a cryptomonad alga Rhodomonas sp. (Cryptophyta, Pyrenomonadaceae) was observed in the chemocline of saline basins separating from the White Sea, resulting in red coloration of the relevant water layer. According to the sequence of the 18S nuclear rRNA gene, this species was identical to Rhodomonas sp. RCC2020 (GenBank accession no. JN934672) from the Beaufort Sea. The presence of the red layer formed by mass development of Rhodomonas sp. is considered an indicator of a certain stage of separation of a basin from the sea.