Differential temperature effects on dissipation of excess light energy and energy partitioning in lut2 mutant of Arabidopsis thaliana under photoinhibitory conditions

The high-light-induced alterations in photosynthetic performance of photosystem II (PSII) and photosystem I (PSI) as well as effectiveness of dissipation of excessive absorbed light during illumination for different periods of time at room (22 °C) and low (8-10 °C) temperature of leaves of Arabidopsis thaliana, wt and lut2, were followed with the aim of unraveling the role of lutein in the process of photoinhibition. Photosynthetic parameters of PSII and PSI were determined on whole leaves by PAM fluorometer and oxygen evolving activity-by a Clark-type electrode. In thylakoid membranes, isolated from non-illuminated and illuminated for 4.5 h leaves of wt and lut2 the photochemical activity of PSII and PSI and energy interaction between the main pigment-protein complexes was determined. Results indicate that in non-illuminated leaves of lut2 the maximum rate of oxygen evolution and energy utilization in PSII is lower, excitation pressure of PSII is higher and cyclic electron transport around PSI is faster than in wt leaves. Under high-light illumination, lut2 leaves are more sensitive in respect to PSII performance and the extent of increase of excitation pressure of PSII, Φ_NO, and cyclic electron transport around PSI are higher than in wt leaves, especially when illumination is performed at low temperature. Significant part of the excessive light energy is dissipated via mechanism, not dependent on ∆pH and to functioning of xanthophyll cycle in LHCII, operating more intensively in lut2 leaves.

The Lack of Lutein Accelerates the Extent of Light-induced Bleaching of Photosynthetic Pigments in Thylakoid Membranes of Arabidopsis thaliana

The high light-induced bleaching of photosynthetic pigments and the degradation of proteins of light-harvesting complexes of PSI and PSII were investigated in isolated thylakoid membranes of Arabidopsis thaliana, wt and lutein-deficient mutant lut2, with the aim of unraveling the role of lutein for the degree of bleaching and degradation. By the means of absorption spectroscopy and western blot analysis, we show that the lack of lutein leads to a higher extent of pigment photobleaching and protein degradation in mutant thylakoid membranes in comparison with wt. The highest extent of bleaching is suffered by chlorophyll a and carotenoids, while chlorophyll b is bleached in lut2 thylakoids during long periods at high illumination. The high light-induced degradation of Lhca1, Lhcb2 proteins and PsbS was followed and it is shown that Lhca1 is more damaged than Lhcb2. The degradation of analyzed proteins is more pronounced in lut2 mutant thylakoid membranes. The lack of lutein influences the high light-induced alterations in organization of pigment-protein complexes as revealed by 77 K fluorescence.

[Efficiency and safety of the intravenous application of esomeprazole (nexium - Astra Zeneca) in high risk patients subjected to mechanic ventilation]

INTRODUCTION

The aim of the research was to determine the effectivity and the safety of the intravenous application of Esomeprazole (Nexium - Astra Zeneca) like prevention of the development of stress-ulcers of the gastric mucous with high risk patients at ICU with mechanic ventilation.

PATIENTS AND METHODS

47 patients subjected to mechanic ventilation over 48 hours with availability of just one more risk factor for development of stress-ulcers of gastric musous were included in the study. Samples of gastric juice for determination of the acidity and presence of fresh erythrocytes and microbiological cultures from gastric contents, wash away of the mouth cavity and tracheal aspiration were tested on the 1st, the 3rd and the 5th day from the start of the treatment. At the end of the therapy there has been determinated the outcome - survivor or died and total quantity of the haemotransfusions.

RESULTS

The acidity of the gastric juice changed in the range over pH 5 during the 24 hours by the application of esomeprazole. Fibrogastroscopic examinations were performed of patients who were found to have fresh erythrocytes in the gastric contents. No one was registered with bleeding of the gastric mucous. The isolated microorganisms of the gastric juice and wash away of mouth cavity were identical with those of tracheobronchial aspiration in about 13 %.

CONCLUSIONS

In our study the application of esomeprazole i.v. was effective and safe approach for profilaxy of the stress-ulcers and the bleeding of the gastric mucous. Comparative studies with H2-blockers and sucralfat are necessary for clarifying and objectifying the significance of the microbiologic isolates of the gastric contents and wash away from mouth cavity and their relation to the development of nosocomial pneumonia.