Three-state mathematical model for the assessment of DCMU-treated photosystem II heterogeneity

Photosystem II (PSII) is one of the main pigment-protein complexes of photosynthesis which is highly sensitive to unfavorable environmental factors. The heterogeneity of PSII properties is essential for the resistance of autotrophic organisms to stress factors. Assessment of the PSII heterogeneity may be used in environmental monitoring for on-line detection of contamination of the environment. We propose an approach to assess PSII oxygen-evolving complex and light-harvesting antenna heterogeneity that is based on mathematical modeling of the shape of chlorophyll a fluorescence rise of 3-(3,4-dichlorophenyl)-1,1-dimethylurea-treated samples. The hierarchy of characteristic times of the processes considered in the model makes it possible to reduce the model to a system of three ordinary differential equations. The analytic solution of the reduced three-state model is expressed as a sum of two exponential functions, and it exactly reproduces the solution of the complete system within the time range from microseconds to hundreds of milliseconds. The combination of several such models for reaction centers with different properties made it possible to use it as an instrument to study PSII heterogeneity. PSII heterogeneity was studied for Chlamydomonas at different intensities of actinic light, for Scenedesmus under short-term heating, and for Chlorella grown in nitrate-enriched and nitrate-depleted media.

Acclimation Response of Green Microalgae Chlorella Sorokiniana to 2,3',4,4',6-Pentachlorobiphenyl

The effect of the toxicant 2,3',4,4',6-pentachlorobiphenyl (PCB-119) on the growth, chlorophyll content, and PSII activity of C. sorokiniana cells was investigated. A strong negative effect of the toxicant was observed at PCB concentration of 0.05 μg mL^-1 , when culture growth ceased, chlorophyll strongly bleached, and cell death occurred. The use of original highly sensitive fluorimeter to measure three types of high-resolution chlorophyll fluorescence kinetics allowed us to detect an initial dramatic decrease in the activity of primary photosynthetic reactions, followed by their almost complete recovery at the end of the incubation period when most cells were dead. The study of the distribution of individual cells in culture in terms of F_v /F_m parameter, which reflects the quantum yield of PSII photochemistry, revealed the existence of 2-3% of cells retaining high F_v /F_m (>0.7) in the presence of the toxicant. The treated cultures were able to resume growth after prolonged incubation in fresh medium. The high sensitivity fluorescence methods used made it possible to identify stress-resistant cells which maintain high photosynthetic activity in the presence of lethal doses of toxic substances; these cells provide recovery of the population after stress.

[Efficiency and safety of phenazopyridine for treatment of uncomplicated urinary tract infection: results of multi-center, randomized, placebo-controlled, clinical study]

AIM

to evaluate the efficiency and safety of phenazopyridine for the treatment of patients with uncomplicated lower urinary tract infection, accompanied by pain.

MATERIALS AND METHODS

A multicenter double-blind, randomized, placebo-controlled study with parallel groups to evaluate the efficacy and safety of phenazopyridine in patients with acute uncomplicated cystitis was performed. A total of 60 women were divided into two groups of 30 patients. In the main group (average age 32.6+/-7.4 years) phenazopyridine was prescribed (2 tablets of 100 mg p.o., with a total dose of 200 mg, once). In the control group, patients (mean age 35.53+/-8.79 years) received a placebo according to the same scheme. To evaluate the efficiency of treatment, the severity of the main symptoms 6 hours after taking the drug was analyzed. After that, patients started antibiotic therapy. They were followed-up for the next three days. The tolerance of therapy was evaluated by the presence of adverse events.

RESULTS

All 30 patients taking phenazopyridine had an improvement after 6 hours, and the most frequent response was "significant improvement" (43.3%). The responses of patients in the main group significantly (p<0.05) differed from responses of patients in the control group. Six hours after taking phenazopyridine/placebo, the severity of all values according to VAS score, including the degree of general discomfort, pain during urination and increased frequency of urination improved significantly in the main group compared to the control group. The average assessment of general discomfort in the main group decreased by 53.4% in comparison with 28.8% in the control group, while the severity of pain during urination and urination frequency decreased by 57.4 vs. 35.9% and 39.6 vs. 27.6%, respectively. An analysis of the time before the complete absence of the general discomfort was performed. In the main group this period of time was significantly less than in the control group (p<0.05). There were no serious adverse events while taking phenazopyridine. Rate of adverse events was comparable between two groups.

CONCLUSION

The results of the study showed that phenazopyridine is an effective and well-tolerated drug for symptomatic therapy in patients with acute uncomplicated cystitis and can be recommended in addition to etiological therapy.

Inhibition of cyanobacterial photosynthetic activity by natural ketones

Microbial volatiles have a significant impact on the physiological functions of prokaryotic and eukaryotic organisms. Various ketones are present in volatile mixtures produced by plants, bacteria, and fungi. Our earlier results demonstrated the inhibitory effects of soil bacteria volatiles, including ketones, on cyanobacteria. In this work, we thoroughly examined the natural ketones, 2-nonanone and 2-undecanone to determine their influence on the photosynthetic activity in Synechococcus sp. PCC 7942. We observed for the first time that the ketones strongly inhibit electron transport through PSII in cyanobacteria cells in vivo. The addition of ketones decreases the quantum yield of primary PSII photoreactions and changes the PSII chlorophyll fluorescence induction curves. There are clear indications that the ketones inhibit electron transfer from Q_A to Q_B , electron transport at the donor side of PSII. The ketones can also modify the process of energy transfer from the antenna complex to the PSII reaction center and, by this means, increase both chlorophyll fluorescence quantum yield and the chlorophyll excited state lifetime. At the highest tested concentration (5 mM) 2-nonanone also induced chlorophyll release from Synechococcus cells that strongly indicates the possible role of the ketones as detergents.

[Effect of mercuric chloride and methylmercury on photosynthetic activity of the diatom Thalassiosira weissflogii by a fluorescent method]

It was shown by the pulse-amplitude modulation fluorescent method that, at a weak illumination (6 microE m-2.s-1), methylmercury at a concentration of 10(-6)-10(-7) M decreases the photochemical activity of the reaction centers of photosystem II in cells of microalgae Thalassiosira weissflogii after a prolonged lag phase. Cells resistant to methylmercury at these low concentrations were detected by the microfluorimetric method. Chloride mercury decreased the activity of photosystem II of the algae only when at higher concentrations. Both toxicants at a concentration of 10(-6) M decreased the rate of recovery of photoinduced damage of centers of photosystem II and led to an increase in the energization component of nonphotochemical fluorescence quenching. These results indicate that the complex of fluorescent methods can be used to monitor early changes in the photosynthetic apparatus of algae in response to the toxic action of heavy metals.