Antagonistic pleiotropy and mutation accumulation contribute to age‐related decline in stress response

As organisms age, the effectiveness of natural selection weakens, leading to age‐related decline in fitness‐related traits. The evolution of age‐related changes associated with senescence is likely influenced by mutation accumulation (MA) and antagonistic pleiotropy (AP). MA predicts that age‐related decline in fitness components is driven by age‐specific sets of alleles, nonnegative genetic correlations within trait across age, and an increase in the coefficient of genetic variance. AP predicts that age‐related decline in a trait is driven by alleles with positive effects on fitness in young individuals and negative effects in old individuals, and is expected to lead to negative genetic correlations within traits across age. We build on these predictions using an association mapping approach to investigate the change in additive effects of SNPs across age and among traits for multiple stress‐response fitness‐related traits, including cold stress with and without acclimation and starvation resistance. We found support for both MA and AP theories of aging in the age‐related decline in stress tolerance. Our study demonstrates that the evolution of age‐related decline in stress tolerance is driven by a combination of alleles that have age‐specific additive effects, consistent with MA, as well as nonindependent and antagonistic genetic architectures characteristic of AP.     

Hydrophobic structure of hairpin ten-ring pyrrole-imidazole polyamides enhances tumor tissue accumulation/retention in vivo

To examine the hydrophobic structure of PI polyamides on tumor accumulation in vivo, PI polyamide-fluorescein conjugates 1–5 with the distinct number of N-methylimidazole (Im) units were synthesized. There existed an inverse relationship between the Im unit number of the compounds and their hydrophobicity. Compound 1 with one Im unit and 3 with three Im units accumulated and retained preferentially in tumor tissues compared to 5 with five Im units. These results suggest the importance of a PI polyamide’s primary structure, which partly contributes to its hydrophobic property, on its accumulation and/or retention in tumor tissues in vivo.     

修复白洋淀镉污染水体的沉水植物筛选试验

为了筛选出适宜修复白洋淀镉(Cd)污染水体的沉水植物,该研究通过室内模拟试验,分析了四种沉水植物黑藻、狐尾藻、金鱼藻和菹草对Cd的耐受性及对底泥Cd的富集和迁移能力。结果表明:(1)通过毒性测试研究,Cd对黑藻、狐尾藻、金鱼藻及菹草的4 d-EC₅₀(半数抑制浓度)分别为0.51、0.81、0.03、0.12 mg·L^-1,狐尾藻对Cd的耐性最强,黑藻次之,金鱼藻对Cd的耐性最低; 四种沉水植物对Cd的最大富集量分别为27.89、15.28、22.54、32.74 g·kg^-1,菹草对Cd的富集能力最强,黑藻次之,狐尾藻对Cd的富集能力最低。(2)通过Cd污染底泥修复研究,黑藻、狐尾藻和菹草体内Cd富集量整体表现为根>叶片和茎(P<0.05); 地上部、根对Cd的富集能力分别表现为黑藻>菹草>狐尾藻,菹草>黑藻>狐尾藻; 三种沉水植物对Cd的迁移能力则表现为黑藻>狐尾藻>菹草。总之,黑藻对底泥中Cd富集和迁移能力均较强,且耐性较高,是最适合修复白洋淀Cd污染水体的沉水植物。     

Phytomonitoring of pulverized fuel ash leachates by the duckweed Lemna minor

The duckweed Lemna minor is one of the smallest vascular plants with a known strong capacity for metal accumulation. L. minor is proposed as a phytomonitor for coal ash drainage systems and for bio-assay studies directed to complexation and speciation. The duration of the experiment can be restricted to fourteen days; it is then possible to determine accurate data of differences in growth of the clone forming plant by using image processing techniques. Leaching of pulverized fuel ash (PFA) with acetic acid according to EPA instruction resulted in effects attributed to the acetic acid itself rather than to the metals in solution. Toxic effects of both leachates, natural and artificial, are discussed. The order of toxicity of metals studied so far in separate metal experiments is Cd > Cu > Zn > As(Arsenite) > Se(Selenite) > Ge > B > Mo.     

Zn uptake by Cladophora glomerata

The uptake of zinc by Cladophora glomerata at different pH-values, light conditions and exposure periods is reported. Zinc uptake was pH-dependent, with uptake increasing with rising pH. Uptake was greatest within the first two hours of exposure and was greater in light than in darkness due to increased pH. All results support the dominance of adsorptive uptake of zinc by Cladophora.     

Effect of one night with "low light'on uptake, reduction and storage of nitrate in spinach

During the night, shoot nitrate concentration in spinach (Spinacia oleracea L. cv. Vroeg Reuzenblad) increased due to increased uptake of nitrate by the roots. When the plants were subjected to a one night “low light’period at 35 μmol m^?2 s^?1, the shoot nitrate concentration did not increase and was reduced by 25% compared to control plants in the dark. The major contribution to this decrease was located in the leaf blades, where the nitrate concentration was decreased by 60%, while the petiole nitrate concentration decreased by only 9%. Nitrate accumulated in the leaf blade vacuoles during a dark night, but this was not the case during the “low light’period. This decrease in vacuolar nitrate concentration, compared to control plants in the dark, was not caused by increased amounts of leaf blade nitrate reductase (NR; EC 1.6.6.1). During a “low light’night period, the cytoplasmic soluble carbohydrate concentration was increased compared to the control plants in the dark. Calculations showed in situ NR activity to be higher than in the control plants in the dark. This increase in NR activity, however, was not large enough to account for the total difference found in the shoot nitrate concentration. Net uptake of nitrate by the roots was increased during the initial hours of the dark night, while vacuolar nitrate concentration in the leaf blades increased at the same time. During the “low light’night period, however, net uptake of nitrate by the roots did not increase, and vacuolar nitrate concentration did not change. We conclude that nitrate uptake by the roots and vacuolar nitrate concentration in the leaf blades are tightly coupled. The decreased shoot nitrate concentration is mainly caused by a reduction in net uptake of nitrate by the roots. During the “low light’night period, carbohydrates and malic acid partly replaced vacuolar nitrate. A “low light’period one night prior to harvest provides a valuable tool to reduce shoot nitrate concentrations in spinach grown in greenhouses in the winter months.     

The role of nitrate in osmoregulation of Italian ryegrass

Summary The role of nitrate in osmotic control was studied with Italian ryegrass grown in a nutrient solution in a climate room. Quantum-flux density, osmotic potential of the nutrient solution and availability of nitrate and chloride were varied independently. Plants at high quantum flux density (650 mol m^–2 s^–1) had a lower osmotic potential, a higher carbohydrate concentration and a lower nitrate concentration than plants at low quantum flux density (310 mol m^–2 s^–1), the decrease in nitrate concentration was osmotically equivalent to the increase in carbohydrate concentration. When nitrate in the nutrient solution was partly replaced by chloride, the chloride taken up substituted an equivalent part of the nitrate in the plant. It is concluded that nitrate plays a role in osmoregulation of the plant and compensates for a shortage of other solutes.     

Effects of abscisic acid on sequestration and exchange of Na+ by barley roots

Excised Na⁺-starved barley roots were suspended in solutions of Na⁺ in combination with NO ₃ ^- , Cl^-, and SO ₄ ^2- , and effects of the added phytohormone, abscisic acid (ABA), to the medium were determined. Abscisic acid increased the rate of Na⁺ (²²Na⁺) accumulation and the amount of Na⁺ deposited in the vacuoles. These stimulating effects of ABA were modified by anions following the sequence NO ₃ ^- >Cl^->SO ₄ ^2- . Testing whether the magnitude of the pH gradient across the plasmalemma of the cells of the root cortex affects rates of Na⁺ accumulation and their dependence upon ABA, we observed that, in the pH range from 4 to 8, the ABA-induced stimulation was strongest at pH 5.8, and least at pH 4. Changes in pH during the experiment caused changes in the rates of Na⁺ accumulation in agreement with experiments performed at constant pH values. Simultaneously with ABA-enhanced accumulation, loss of Na⁺ occurred. Loss of Na⁺ was strongest at pH 4 and was affected by anions, being greatest with SO ₄ ^2- and following the sequence SO ₄ ^2- >Cl^->NO ₃ ^- . On the basis of the finding that initial acceleration of uptake as well as loss of Na⁺ depended on the pH of the medium we suggest that, in barley roots, ABA stimulates an exchange of Na⁺ for H⁺ at the plasmalemma of the cortical cells. The results indicate that ABA-stimulated expulsion of Na⁺, in combination with ABA-stimulated sequestration in the vacuoles, constitutes one of the mechanisms which enable barley plants to tolerate higher than normal levels of Na⁺.Abbreviations ABA abscisic acid - FW fresh weight     

Osmoregulation by potassium transport in Escherichia coli

Abstract Cell turgor pressure determines the extent of K⁺ accumulation by Escherichia coli cells. K⁺ influx is mediated both by a constitutive system with a low affinity for K⁺ (Trk) and by an inducible high affinity system (Kdp). K⁺ efflux is controlled by as yet unidentified but independent systems. Cell K⁺ concentration may be the link between growth in media of high osmolarity and the concomitant accumulation of compatible solutes such as betaine.