The oxygen effect in haploid and diploid yeast strains of different sensitivities

The extent of the oxygen effect for cell survival was studied in diploid and haploid wild-type yeast and in mutants beloning to the rad2, rad6 and rad50 epistatic group. In haploids, reduced oxygen enhancement ratios were found in rad52, rad6 and rad18. The latter two also showed some influence of the mating type. In diploids the oxygen effect was decreased in rad2, rad52 and rad18.     

Diploidy and repair of radiation damage in Saccharomyces mutants

Diploid wild-type cells of Saccharomyces and cells homozygous for one of the single genes r^s₁, r^s₂ of the two alleles of the r^s₃ gene (rad 2 gene) were tested for their response to ionizing irradiation in the presence and absence of oxygen. Both immediate and delayed plating (agar-holding) techniques were used.An identical oxygen enhancement ratio (OER) of 2.5 was observed in r^s₁r^s₁, r^s₂r^s₂ cells and the wild type. In r^s_3?1r^s_3?1 and r^s_3?2r^s_3?2 cells the OER was reduced. Their sensitivity to ionizing irradiation in oxic conditions was the same as that of the wild type.r^s₂r^s₂ cells showed an increase in relative sensitivity by a factor of 4 in both conditions of irradiation. The relative sensitivity of r^s₁r^s₁ cells was increased by a factor of 2.5 in hypoxic conditions and the sensitivity in hypoxia was identical to that of wild type cells in oxic conditions. In contrast to haploid r^s₁ cells the oxygen effect was fully expressed in diploid r^s₁r^s₁ cells.The results on diploid strains are discussed in terms of three independent genetically determined repair systems in Saccharomyces. The expression of these systems is influenced by ploidy.     

HIF-1 and NDRG2 contribute to hypoxia-induced radioresistance of cervical cancer Hela cells

Hypoxia inducible factor 1 (HIF-1), the key mediator of hypoxia signaling pathways, has been shown involved in hypoxia-induced radioresistance. However, the underlying mechanisms are unclear. The present study demonstrated that both hypoxia and hypoxia mimetic cobalt chloride could increase the radioresistance of human cervical cancer Hela cells. Meanwhile, ectopic expression of HIF-1 could enhance the resistance of Hela cells to radiation, whereas knocking-down of HIF-1 could increase the sensitivity of Hela cells to radiation in the presence of hypoxia. N-Myc downstream-regulated gene 2 (NDRG2), a new HIF-1 target gene identified in our lab, was found to be upregulated by hypoxia and radiation in a HIF-1-dependent manner. Overexpression of NDRG2 resulted in decreased sensitivity of Hela cells to radiation while silencing NDRG2 led to radiosensitization. Moreover, NDRG2 was proved to protect Hela cells from radiation-induced apoptosis and abolish radiation-induced upregulation of Bax. Taken together, these data suggest that both HIF-1 and NDRG2 contribute to hypoxia-induced tumor radioresistance and that NDRG2 acts downstream of HIF-1 to promote radioresistance through suppressing radiation-induced Bax expression. It would be meaningful to further explore the clinical application potential of HIF-1 and NDRG2 blockade as radiosensitizer for tumor therapy.     

Photoacoustic characteristics of leaves of atrazine-resistant weed mutants

The photosynthetic characteristics of leaves of atrazine-resistant and-susceptible biotypes of several weed species (Solanum nigrum, Senecio vulgaris, Epilobium ciliatum and Chenopodium album) were compared using the photoacoustic method. Analysis of the dependence of the photoacoustic signal of the modulation frequency indicated that, in Solanum, Epilobium and Senecio, the relative quantum yield of O₂ evolution (estimated by the ratio of the amplitude of the O₂ signal, A_OX, to that of the photothermal signal, A_PT) was substantially reduced in the atrazine-resistant mutant, without any changes in the O₂ diffusion characteristics of the leaves. In contrast, in Chenopodium, atrazine-resistance was associated with a concomitant change in and in the leaf diffusion parameters. This latter change suggests that the leaf internal anatomy was modified in the resistant Chenopodium. Measurements of the Emerson enhancement indicated that the reduction of observed in the atrazine-resistant mutants was caused by a marked decrease in the photochemical potential of PS II (). The study of the light intensity dependence of the A_OX/A_PT ratio showed that saturation of O₂ evolution occurred at the same light level (around 2000 mol m^-2 s^-1) in both types of plants. However, the relative maximal rate of O₂ evolution was slightly lower (-10%) in the atrazine-resistant biotype as compared to the wild type. Reduced and light-saturated rate of O₂ evolution were also measured in atrazine-resistant weed biotypes using a conventional Clark-type O₂ electrode.Abbreviations A_OX modulated O₂ evolution component of the photoacoustic signal - A_PT photothermal component of the photoacoustic signal - Atrazine 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine - E Emerson enhancement - PS II and PS I photosystems II and I, respectively - Q_A primary electron acceptor of PS II - Q_B secondary electron acceptor of PS II - quantum yield of O₂ evolution     

Modelling the isotope enrichment of leaf water

Farquhar and Gan [10] have proposed a model for the spatial variation in the isotopic enrichment of H₂¹⁸O across a leaf, which is specifically formulated for monocotyledoneous leaves. The model is based on the interaction between mass fluxes longitudinally within the xylem, and fluxes laterally through veinlets into the lamina mesophyll, where moisture leaves the leaf through transpiration. The lighter, more abundant, molecule H₂¹⁶O escapes preferentially with the evaporating water, resulting in the enrichment of H₂¹⁸O at these sites. Enriched water diffuses throughout the leaf, and it is this spatial distribution of enriched water which the model seeks to capture. In this paper we present a general formulation of the model in terms of mass flux, extending it to include variable transpiration rates across the leaf surface, as well as a tapering xylem. Solutions are developed for the general case and, since the solutions present in the form of Kummer functions, properties are established as well as methods for estimating the solutions under certain conditions relevant to the biology. The model output is compared with Gans data ([14, 15]) collected from maize plants.     

Local resource competition and local resource enhancement shape primate birth sex ratios

Sex ratio theory provides a powerful source of testable predictions about sex allocation strategies. Although studies of invertebrates generally support predictions derived from the sex ratio theory, evidence for adaptive sex ratio biasing in vertebrates remains contentious. This may be due to the fact that most studies of vertebrates have focused on facultative adjustment in relation to maternal condition, rather than processes that might produce uniform sex biases across individuals. Here, we examine the effects of local resource enhancement (LRE) and local resource competition (LRC) on birth sex ratios (BSRs). We also examine the effects of sex differences in the costs of rearing male and female offspring on BSRs. We present data from 102 primate species and show that BSRs are skewed in favour of the dispersing sex in species that do not breed cooperatively, as predicted by the LRC model. In accordance with the LRE model, BSRs are generally skewed in favour of the more beneficial sex in cooperatively breeding primate species. There is no evidence that BSRs reflect the extent of sexual size dimorphism, an indirect measure of the costs of rearing male and female offspring. These analyses suggest that adaptive processes may play an important role in the evolution of BSRs in vertebrates.     

The effects of intensity of exercise on excess postexercise oxygen consumption and energy expenditure in moderately trained men and women

This experiment investigated the effects of intensity of exercise on excess postexercise oxygen consumption (EPOC) in eight trained men and eight women. Three exercise intensities were employed 40%, 50%, and 70% of the predetermined maximal oxygen consumption (VO_2max). All ventilation measured was undertaken with a standard, calibrated, open circuit spirometry system. No differences in the 40%, 50% and 70% VO_2max trials were observed among resting levels of oxygen consumption (V0₂) for either the men or the women. The men had significantly higher resting VO₂ values being 0.31 (SEM 0.01) 1·min^–1 than did the women, 0.26 (SEM 0.01) 1·min^–1 (P < 0.05). The results indicated that there were highly significant EPOC for both the men and the women during the 3-h postexercise period when compared with resting levels and that these were dependent upon the exercise intensity employed. The duration of EPOC differed between the men and the women but increased with exercise intensity: for the men 40% – 31.2 min; 50% – 42.1 min; and 70% – 47.6 min and for the women, 40% – 26.9 min; 50% – 35.6 min; and 70% – 39.1 min. The highest EPOC, in terms of both time and energy utilised was at 70% VO_2max. The regression equation for the men, where y=O₂ in litres, and x=exercise intensity as a percentage of maximum was y=0.380x + 1.9 (r ²=0.968) and for the women is y=0.374x–0.857 (r ²=0.825). These findings would indicate that the men and the women had to exercise at the same percentage of their VO_2max to achieve the maximal benefits in terms of energy expenditure and hence body mass loss. However, it was shown that a significant EPOC can be achieved at moderate to low exercise intensities but without the same body mass loss and energy expenditure.