The Melatonin Receptor CAND2/PMTR1 Is Involved in the Regulation of Mitochondrial Gene Expression under Photooxidative Stress.

Melatonin is a signaling molecule that mediates multiple stress-dependent reactions. Under photooxidative stress conditions generating intensive ROS production, exogenous melatonin (50 µM) contributed to maintaining the expression of mitochondrial encoded genes and up-regulation of RNA-polymerase genes RPOTm and RPOTmp, operating through the CAND2 receptor and α-subunit of the heterotrimeric G protein GPA1 coupled with CAND2. Unlike wild-type plants, mutants with defective CAND2 and GPA1 genes exhibited no decrease in the alternative pathway of leaf respiration, as well as the activity of an alternative oxidase, and the expression of the AOX1a gene. At the same time, the protective effect of exogenous melatonin on some physiological indicators did not depend on the receptor and was associated with the direct antioxidant function of the regulator. Thus, melatonin under photooxidative stress conditions can act as an antioxidant and as a hormone capable of regulating the expression of nuclear and organelle genes through the components of melatonin signal perception.

Cold Stress Activates the Expression of Genes of the Chloroplast Transcription Apparatus in Arabidopsis thaliana Plants.

The physiological and molecular responses of Arabidopsis thaliana plants to cold stress were studied. Exposure to a low non-freezing temperature (4°C, 5 days) caused a decrease in the physiological functions and activity of a number of photosynthetic genes and elevation in expression of the cold stress gene COR15a, the product of which protects chloroplasts. It was shown for the first time that in parallel to a general inhibition of physiological functions under hypothermia, an increase in the expression of most genes for the chloroplast transcription apparatus was observed. This is obviously one of the compensatory mechanisms of adaptation aimed to maintain cellular homeostasis and physiological functions under hypothermia.

Cytokinins and Abscisic Acid Regulate the Expression of the Genes for Plastid Transcription Apparatus during Heat Shock.

The treatment of Arabidopsis thaliana plants with exogenous cytokinin (CK) followed by heat shock (HS) activated the expression of the genes for the plastid transcription machinery but adversely affected the plant viability. Abscisic acid (ABA), conversely, promoted maintaining the resistance to HS and had differentially affected different components of the plastid transcriptional complex. This hormone suppressed the accumulation of transcripts of PEP genes and the genes encoding PAP proteins, which are involved in DNA-RNA metabolism. However, it had no effect or activated the expression of NEP genes and PAP genes, which are involved in the redox regulation, as well as the genes encoding the stress-inducible trans-factor (SIG5) and the plastid transcription Ser/Thr protein kinase (cpCK2). Thus, for the adaptation of plants to elevated temperatures, both increase and decrease in the expression of the genes for the plastid transcriptional machinery with the involvement of various regulatory systems, including phytohormones, are equally significant.

[Evolution of subpopulations of cells of transplantable tumors following x-ray irradiation]. / Evoliutsiia subpopuliatsii kletok perevivaemykh opukholei posle rentgenovskogo oblucheniia.

The paper is devoted to a study of the structure of subpopulations of 3 experimental tumors (ascitic Ehrlich carcinoma, melanoma B-16 and Lewis lung adenocarcinoma) in their progression and following single local X-radiation. At the same time some functional indices of cell viability were investigated over time: intracellular pH, intensity of respiration, the level of cell protein, the level of lipid peroxidation (according to the content of one of its end-products--malonic dialdehyde). Considerable differences of subpopulations within one tumor and between different tumor types were established. The relationship of functional differences of these subpopulations with the clonogenicity of forming cells was shown. X-radiation caused inhomogeneous changes in the structure of subpopulations, the above indices changed. The authors have analyzed the regularity of these changes, their relationship with radiosensitivity or radioresistance of tumor cell subpopulations.

[Potentiation of the selective antitumoral effect of cyclophosphamide and 5-fluorouracil by its combination with amphotericin B and diacarb]. / Povyshenie izbiratel'nosti protivoopukholevogo deistviia tsiklofosfana i 5-ftoruratsila pri ikh sochetanii s amfoteritsinom B i diakarbom.

The paper deals with the results of experiments which were carried out on 10 tumor models and used approximately 1,000 animals (mice and rats of different strains). Such cytostatic drugs as cyclophosphamide (alkylating agent) and 5-fluorouracil (antimetabolite) showed a significantly enhanced antitumor and metastation--preventing effect when used in combination with polyene antibiotic amphotericin B and a diuretic drug--diacarb. This was matched by a pronounced amelioration of toxic side effects and an increase in the animals' lifespan. The said method of treatment should be integrated with oncological practice.

[Effect of amphotericin B on the diuretic action of diacarb and various indicators of water-salt metabolism in healthy and tumor-bearing animals]. / Vliianie amfoteritsina B na diureticheskii éffekt diakarba i nekotorye pokazateli vodno-solevogo obmena u zdorovykh zhivotnykh i zhivotnykh s opukholiami.

The experiments with albino rats, Wistar rats and SHK mice showed that the combined use of amphotericin B and diacarb markedly potentiated the effect of the latter: the amount of the urine excreted within 6 h and the renal excretion of sodium ions increased 1.8 and 1.5 times, respectively. Analogous trends were observed in the experiments with stabilization of the animal water balance by 2 per cent water loading. The studies on rats with Pliss lymphosarcoma showed that the diuresis level in the tumor-bearing animals was 3 times lower than that in healthy rats. The treatment with 5-fluorouracil lowered this index more significantly. With the use of amphotericin B, diacarb and their combination the urination level came to normal. The cyclophosphamide therapy of mice with sarcoma 180 was accompanied by accumulation of water in the tumor tissue. The combined use of the cytostatic with the polyenic antibiotic and diuretic resulted in a significant lowering of this index. In rats with Walker-256 carcinosarcoma, the treatment with the above three drugs lowered the sodium ion concentration and increased the calcium ion concentration in the tumor tissue. At the same time the electrolyte level in some organs not affected with malignant tumor (spleen, thymus, liver and adrenal glands) returned to normal.