Suppression of mitochondrial alternative oxidase can result in upregulation of the ROS scavenging network: some possible mechanisms underlying the compensation effect

Mitochondrial alternative oxidase is an important protein involved in maintaining cellular metabolic and energy balance, especially under stress conditions. AOX genes knockout is aimed at revealing the functions of AOX genes. Under unfavourable conditions, AOX-suppressed plants (mainly based on Arabidopsis AOX1a-knockout lines) usually experience strong oxidative stress. However, a compensation effect, which consists of the absence of AOX1a leading to an increase in defence response mechanisms, concomitant with a decrease in ROS content, has also been demonstrated. This review briefly describes the possible mechanisms underlying the compensation effect upon the suppression of AOX1a. Information about mitochondrial retrograde regulation of AOX is given. The importance of ROS and mitochondrial membrane potential in triggering the signal transmission from mitochondria in the absence of AOX or disturbance of mitochondrial electron transport chain functions is indicated. The few available data on the response of the cell to the absence of AOX at the level of changes in the hormonal balance and the reactions of chloroplasts are presented. The decrease in the relative amount of reduced ascorbate at stable ROS levels as a result of compensation in AOX1a-suppressed plants is proposed as a sign of stress development. Obtaining direct evidence on the mechanisms and signalling pathways involved in AOX modulation in the genome should facilitate a deeper understanding of the role of AOX in the integration of cellular signalling pathways.     

Prolongation of oxidative stress by long-lived reactive protein species induced by X-ray radiation and their genotoxic action

Abstract The formation of long-lived reactive protein species of bovine serum albumin (BSA), ovalbumin, casein and casein hydrolyzate with a half-life of 3-5 hours was shown using chemiluminescence induced by X-ray radiation. It was found that long-lived reactive protein species are capable of generating reactive oxygen species (ROS) (H(2)O(2), OH(?), HO(2)(?, 1)O(2)) in the aquatic environment over a long period of time in vitro. The interaction of X-ray-irradiated BSA with DNA in vitro led to the formation of 8-oxoguanine (8-oxo-7,8-dihydroguanine), a biomarker of oxidative damage to DNA. Some natural antioxidants are effective scavengers of ROS (inosine, tryptophan, methionine and ascorbate). They protect DNA from the action of long-lived reactive protein species leading to ROS generation and the formation of 8-oxoguanine. The intravenous injection of X-ray radiation-induced, long-lived reactive protein species to rats, as well as the peroral and intraperitoneal administration of these products to mice, gave rise to cytogenetic injuries in the cells of their red bone marrow through the formation of micronuclei in polychromatophilic erythrocytes. The administration of the same natural antioxidants used for in vitro experiments soon after irradiation made it possible to effectively eliminate the genotoxic action of oxidative stress caused by radiation-induced, long-lived reactive protein species. Our data represent clear evidence that the oxidative damage to proteins induced by X-rays is directly involved in the induction of a response to DNA damage in rodents.     

The effect of interleukin-2 on experimental emotional hypertension]

The effect of human recombinant interleukin-2, one of the potent mediators of the immune system, on the course of emotional hypertension in non-linear white rats has been investigated. A significant and prolonged hypotensive action of a single injection of interleukin-2 in hypertensive rats has been revealed. The data obtained can be a new evidence of participation of immune system in the development of hypertension in experimental animals.     

Long-lived radicals of amino acids induced by X-ray-radiation are the source of hydrogen peroxide in aqueous medium

The formation of long-lived radicals in the solutions of casein and its hydrolysate with an equimolar mixture of amino acids was compared by measuring the X-ray-induced chemiluminescence. It was shown that free amino acids constituting the protein produce long-lived radicals. It was demonstrated that some amino acids (Leu, Ile, Val, Ser, Trp, Met, Pro, Arg, Gly, Phe) emit light of visible spectrum over a long period of time after the irradiation, which indicates the generation of long-lived radicals of these amino acids. The half-life times of these radicals are several hours. Dissolving irradiated dry amino acids capable of luminescing over a long time gives rise to the formation of hydrogen peroxide in aqueous medium.     

Polymorphism of the apolipoprotein E gene (APOE) in the populations of Russia and neighboring countries

Allele and genotype frequencies for the locus encoding apolipoprotein E, involved in the regulation of lipid metabolism (APOE), were evaluated in 16 populations representing 12 ethnic groups (a total of 1103 subjects) from Russia and neighboring countries. In the populations examined, the frequencies of allele epsilon4, which is the risk factor of Alzheimer's disease and coronary heart disease, varied from less than 5 to more than 20%, while the variation of the major epsilon3 allele in these populations ranged from less than 75 to 95%. The frequencies of alleles epsilon3 and epsilon4 were 0.714 and 0.205 in Saami, 0.734 and 0.149 in Maris, 0.841 and 0.122 in Evenks, 0.788 and 0.163 in Buryats, 0.764 and 0.202 in Chukchi, 0.875 and 0.075 in Iranians, 0.956 and 0.044 in mountain-dwellers of the Pamirs, 0.771 and 0.094 in Ukrainians, and 0.795 and 0.091 in Belarussians, respectively. In Russians from different regions of the country, the frequencies of these alleles were 0.728 and 0.139 (Kostroma), 0.795 and 0.105 (Moscow), 0.857 and 0.092 (Rostov-on-Don), and 0.824 and 0.083 (Krasnodar), respectively. The latitudinal distribution of the APOE epsilon3 and epsilon4 allele frequencies in the populations examined was comparable to the frequency distribution pattern of these alleles in other populations of Eurasia.     

Polymorphism of the apolipoprotein E gene (APOE) in the populations of Russia and neighboring countries

Allele and genotype frequencies for the locus encoding apolipoprotein E, involved in the regulation of lipid metabolism (APOE), were evaluated in 16 populations representing 12 ethnic groups (a total of 1103 subjects) from Russia and neighboring countries. In the populations examined, the frequencies of allele ?4, which is the risk factor of Alzheimer’s disease and coronary heart disease, varied from less than 5 to more than 20%, while the variation of the major ?3 allele in these populations ranged from less than 75 to 95%. The frequencies of alleles ?3 and ?4 were 0.714 and 0.205 in Saami, 0.735 and 0.220 in Komi-Izhemts, 0.770 and 0.130 in Komi-Zyryans, 0.771 and 0.149 in Udmurts, 0.734 and 0.149 in Maris, 0.841 and 0.122 in Evenks, 0.788 and 0.163 in Buryats, 0.764 and 0.202 in Chukchi, 0.875 and 0.075 in Iranians, 0.956 and 0.044 in mountain-dwellers of the Pamirs, 0.771 and 0.094 in Ukrainians, and 0.795 and 0.091 in Belarussians, respectively. In Russians from different regions of the country, the frequencies of these alleles were 0.728 and 0.139 (Kostroma), 0.795 and 0.105 (Moscow), 0.857 and 0.092 (Rostov-on-Don), and 0.824 and 0.083 (Krasnodar), respectively. The latitudinal distribution of the APOE ?3 and ?4 allele frequencies in the populations examined was comparable to the frequency distribution pattern of these alleles in other populations of Eurasia.     

Temperature Controls a Dependence of Barley Plant Growth on Mineral Nutrition Level

The effect of temperature regime on growth and other morphological characteristics of barley plants (Hordeum distichum L., cv. Andrei) as dependent on the level of mineral nutrition was investigated in a controlled experiment. Plants were raised hydroponically at a high (0.22 g/(g day)) and low (0.05 g/(g day)) relative rates of the addition of mineral nutrients (R _A). Mineral nutrients were daily added to the nutrient solutions in exponentially increased amounts to provide steady-state plant growth. At the optimum temperature regime (21/17°C, day/night), the plant relative growth rate (RGR) was proportional to the preset R _A during the entire exponential period. Low R _A led to a decrease in the nitrogen content in plants, plant weight, and respiratory activity, as well as to the increase in the relative root weight. Biomass accumulation at lowered temperature regime (13/8°C) and a high R _A was 1.8-fold lower than at optimum temperature regime. Although under these conditions, the ratio of respiration to gross photosynthesis reduced threefold due to the decrease in the respiration rate, RGR of plants was equal to 0.11 ± 0.02 g/(g day), which was twice lower than the preset R _A. These pointed to the decrease in plant ability to maintain a certain ratio of photosynthesis to respiration within a day. At a deficiency of mineral nutrition and low temperature, RGR reached the preset R _A. Plants adapted to lowered temperature by a shift of the temperature optimum of their metabolism (heat production) to lower values. As a whole, a low variability of such growth parameters as RGR, C/N, and root to shoot weight ratio at different R _A and lowered temperatures testified to the lessening of growth limitation by the mineral nutrition.__________Translated from Fiziologiya Rastenii, Vol. 52, No. 3, 2005, pp. 384–391.Original Russian Text Copyright © 2005 by Garmash.     

Activities of respiratory pathways and the pool of nonstructural carbohydrates in greening leaves of spring wheat seedlings

Seedlings of spring wheat (Triticum aestivum L.) were used to study the dynamics of leaf respiration, the respiratory pathway ratio, and relation of activities of these pathways to the content of soluble carbohydrates in the leaf during greening of seedlings for 48 h under continuous photosynthetically active light (190 μmol/(m² s)). Changes in leaf respiration during de-etiolation were closely related to modulation of the alternative respiratory pathway (AP) activity. The rate of cytochrome respiratory pathway (CP) depended directly on the carbohydrate content and growth rate. These relations suggest that the substrate regulation of CP activity during greening is mediated by the energy needs for growth and is effectively regulated by the mechanism of respiratory control. The highest rates of AP were observed after a 6-h exposure of seedlings to light. The proportion of CP/AP at this stage was close to unity. The temporal pattern of AP activity during de-etiolation was independent on the content of soluble carbohydrates. Hence, in addition to substrate regulation of AP, there are other intricate mechanisms of AP involvement. Our results are in accordance to the state that the alternative respiratory pathway participates in maintaining homeostasis in phototrophic cells during development of the photosynthetic function.     

Long-lived radicals of amino acids induced by X-ray radiation are the source of hydrogen peroxide in aqueous medium

Formation of long-lived radicals in solutions of casein and its hydrolysate with an equimolar mixture of amino acids was compared by measuring the X-ray-induced chemiluminescence. It was shown that free amino acids constituting the protein produce long-lived radicals. It was demonstrated that some amino acids (Leu, Ile, Val, Ser, Trp, Met, Pro, Arg, Gly, Phe) emit light of visible spectrum over a long period of time after irradiation, which indicates generation of long-lived radicals of these amino acids. The half-life times of these radicals are several hours. Dissolution of irradiated dry amino acids capable of luminescing over a long time causes formation of hydrogen peroxide in the aqueous medium.