Seasonal dynamics of soil micronutrients in compost-amended bermudagrass turf

Compost application to turfgrasses can increase plant-available nutrient concentrations in soil and improve growth, but may alter micronutrient dynamics and increase leaching and runoff losses. The objectives of this study were to investigate the influence of compost on the seasonal dynamics of plant-available Mn, Fe, Cu, and Zn in soil after a single application to bermudagrass [Cynodon dactylon (L.) Pers.] turf. Extractable Mn increased from 270 to 670 mg kg(-1) and Cu from 0.36 to 9.89 mg kg(-1) from 0 to 29 months. In contrast, extractable Fe and Zn decreased by 52% and 57% during the same time period. Seasonal trends in extractable Mn and Cu were closely related to dissolved organic C (DOC), and appeared influenced by bermudagrass growth and dormancy patterns and subsequent impacts on DOC. Losses of Mn and Cu from the soil surface occurred after high levels of precipitation during winter dormancy but not during the growing season, while Fe and Zn exhibited an opposite pattern. Thus, seasonal variation of soil micronutrients was likely related to seasonal patterns of bermudagrass growth and dormancy and their effects on DOC, and precipitation events which probably leached DOC and complexed nutrients from surface soil. Composts only influenced the magnitude of changes in micronutrient concentrations, as similar seasonal trends occurred for both compost-amended and unamended soils.     

Conformational relaxation following hydride transfer plays a limiting role in dihydrofolate reductase catalysis

The catalytic cycle of an enzyme is frequently associated with conformational changes that may limit maximum catalytic throughput. In Escherichia coli dihydrofolate reductase, release of the tetrahydrofolate (THF) product is the rate-determining step under physiological conditions and is associated with an "occluded" to "closed" conformational change. In this study, we demonstrate that in dihydrofolate reductase the closed to occluded conformational change in the product ternary complex (E.THF.NADP (+)) also gates progression through the catalytic cycle. Using NMR relaxation dispersion, we have measured the temperature and pH dependence of microsecond to millisecond time scale backbone dynamics of the occluded E.THF.NADP (+) complex. Our studies indicate the presence of three independent dynamic regions, associated with the active-site loops, the cofactor binding cleft, and the C-terminus and an adjacent loop, which fluctuate into discrete conformational substates with different kinetic and thermodynamic parameters. The dynamics of the C-terminally associated region is pH-dependent (p K a < 6), but the dynamics of the active-site loops and cofactor binding cleft are pH-independent. The active-site loop dynamics access a closed conformation, and the accompanying closed to occluded rate constant is comparable to the maximum pH-independent hydride transfer rate constant. Together, these results strongly suggest that the closed to occluded conformational transition in the product ternary complex is a prerequisite for progression through the catalytic cycle and that the rate of this process places an effective limit on the maximum rate of the hydride transfer step.     

Antioxidant enzymes, free-radical damage, and response to paraquat in liver and kidney of long-living growth hormone receptor/binding protein gene-disrupted mice.

Numerous studies have shown that the lifespan can be extended by caloric restriction or by altering the growth hormone (GH)-insulin-like growth factor 1 signaling pathway. Both of these manipulations produce physiological alterations, such as increased insulin sensitivity, and reduced glucose levels and body size. However, it is difficult to evaluate whether these are merely correlates of delayed aging or whether they have a direct causal effect on lifespan. One parameter that has been demonstrated to have causal, positive effects on longevity in invertebrates is improved antioxidant defenses. We measured activities of antioxidant enzymes Cu/Zn superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) and quantified free-radical damage by lipid peroxidation (LP) and protein oxidation (PO) measurements in liver and kidney tissues, and evaluated the response to paraquat-induced oxygen toxicity in the long-living GH receptor/binding protein gene knockout (GHR-KO) mouse. We found that in the kidney, SOD was lower and GPx was higher in GHR-KO mice, and LP was higher in female GHR-KO mice only. In the liver, female GHR-KO mice had lower GPx, while male GHR-KO mice had lower CAT and higher LP. GHR-KO males were also more susceptible to paraquat toxicity compared to females or normal males. We conclude that in long-living GHR-KO mice, GH-resistance does not confer longevity by improved free-radical scavenging in the liver and kidney, suggesting that greater free-radical defenses in other tissues, or altered glucose metabolism may have a more central role in extending the lifespan of these animals.     

Large contribution of arbuscular mycorrhizal fungi to soil carbon pools in tropical forest soils

The origins and composition of soil organic matter (SOM) are still largely uncertain. Arbuscular mycorrhizal fungi (AMF) are recognized as indirect contributors through their influence on soil aggregation, plant physiology, and plant community composition. Here we present evidence that AMF can also make large, direct contributions to SOM. Glomalin, a recently discovered glycoprotein produced by AMF hyphae, was detected in tropical soils in concentrations of over 60 mg cm^–3. Along a chronosequence of soils spanning ages from 300 to 4.1 Mio years, a pattern of glomalin concentrations is consistent with the hypothesis that this protein accumulates in soil. Carbon dating of glomalin indicated turnover at time scales of several years to decades, much longer than the turnover of AMF hyphae (which is assumed to be on the order of days to weeks). This suggests that contributions of mycorrhizae to soil carbon storage based on hyphal biomass in soil and roots may be an underestimate. The amount of C and N in glomalin represented a sizeable amount (ca. 4–5%) of total soil C and N in the oldest soils. Our results thus indicate that microbial (fungal) carbon that is not derived from above- or below-ground litter can make a significant contribution to soil carbon and nitrogen pools and can far exceed the contributions of soil microbial biomass (ranging from 0.08 to 0.2% of total C for the oldest soils).     

Nucleotide-Dependent Isomerization of Glutamate Dehydrogenase in Relation to Total RNA Contents of Peanut

The physiological function of glutamate dehydrogenase (GDH) was investigated by treating germinating peanut (Arachis hypogaea L.) seeds with nucleoside triphosphate (NTP) solutions in order to alter the isoenzyme distribution patterns. The free nucleosides and nucleotides of the GTP-treated peanut were the highest [8.7 μmol g⁻¹(f.m.)], and they decreased through the ATP-treated peanut [5.8 μmol g⁻¹(f.m.)], and CTP-treated peanut [5.5 μmol g⁻¹(f.m.)], to the UTP-treated peanut [4.1 μmol g⁻¹(f.m.)]. The combination of 4 NTPs induced 20 % higher content of Pi [173 nmol g⁻¹(f.m.)] than in the control, but the combined ATP+UTP treatment induced the lowest (93.0 nmol g⁻¹(f.m.)] Pi. The 4 NTP treatment also induced the highest number of GDH isoenzymes (28) followed by the purine NTP treatments (15 to 20), but the pyrimidine NTP treatments and the combined purine + pyrimidine NTP treatments induced the lowest numbers (<15) of isoenzymes. The deamination/amination ratios were generally higher in the UTP (0.11), and CTP (0.06) treated peanuts than in the GTP (0.04), and ATP (0.07) treated peanuts. There were mutual relationships between higher numbers of GDH isoenzymes present in the GTP-, and ATP-treated peanuts and higher RNA (236.5 and 239.4 μg g⁻¹, respectively) contents on one hand, and between the lower numbers of isoenzymes in the CTP-, and UTP-treated peanuts and lower RNA (162.0 and 152.5 μg g⁻¹, respectively) contents. The recurrent relationships of the effects of the NTP treatments of peanut were UTP > ATP > CTP > GTP. This revised version was published online in July 2006 with corrections to the Cover Date.     

Detergent-resistant membrane fractions contribute to the total 1H NMR-visible lipid signal in cells.

Leukocytes and other cells show an enhanced intensity of mobile lipid in their 1H NMR spectra under a variety of conditions. Such conditions include stimulation, which has recently been shown to involve detergent-resistant, plasma membrane domains (DRMs) often called lipid rafts. As there is much speculation surrounding the origin of cellular NMR-visible lipid, we analysed subcellular fractions, including DRMs, by NMR spectroscopy. We demonstrated that DRMs isolated by density gradient centrifugation from lymphoid (CEM-T4, stimulated Jurkat cells), and monocytoid (THP-1) cells produced NMR-visible, lipid signals. Large scale subfractionation of THP-1 cells determined that while cytoplasmic lipid droplets constituted much of the total NMR-visible lipid, the contribution of DRMs was significant. Qualitative and quantitative lipid analyses revealed that DRMs and lipid droplets differed in their lipid composition. DRMs were enriched in cholesterol and ganglioside GM1, and contained relatively unsaturated fatty acids compared with the lipid droplets. Both lipid droplets and DRMs contained neutral lipids (triacylgycerols, cholesterol ester, fatty acids in THP-1 cells) that could, in addition to phospholipids, contribute to the NMR-visible lipid. The lipid droplets also exhibited different protein profiles and contained 500-fold less protein than DRMs, confirming that DRMs and droplets were fractionated as separate entities. The NMR-visible lipid in DRMs is therefore unlikely to be a contaminant from lipid droplets. We propose a micropartitioning of the NMR-visible mobile lipid of whole cells between intracellular lipid droplets, where most of this lipid resides, and detergent-resistant plasma membrane domains.     

Inter and intra‐population variation in shoaling and boldness in the zebrafish (Danio rerio)

Population differences in anti‐predator behaviour have been demonstrated in several species, although less is known about the genetic basis of these traits. To determine the extent of genetic differences in boldness (defined as exploration of a novel object) and shoaling within and between zebrafish ( Danio rerio ) populations, and to examine the genetic basis of shoaling behaviour in general, we carried out a study that involved laboratory‐raised fish derived from four wild‐caught populations. Controlling for differences in rearing environment, significant inter‐population differences were found in boldness but not shoaling. A larger shoaling experiment was also performed using one of the populations as the basis of a North Carolina type II breeding design (174 fish in total) to estimate heritability of shoaling tendency. A narrow‐sense heritability estimate of 0·40 was obtained, with no apparent dominance effects.