Photosystem II Excitation Pressure and Photosynthetic Carbon Metabolism in Chlorella vulgaris

Chlorella vulgaris grown at 5[deg]C/150 [mu]mol m-2 s-1 mimics cells grown under high irradiance (27[deg]C/2200 [mu]mol m-2 s-1). This has been rationalized through the suggestion that both populations of cells were exposed to comparable photosystem II (PSII) excitation pressures measured as the chlorophyll a fluorescence quenching parameter, 1 - qP (D.P. Maxwell, S. Falk, N.P.A. Huner [1995] Plant Physiol 107: 687-694). To assess the possible role(s) of feed-back mechanisms on PSII excitation pressure, stromal and cytosolic carbon metabolism were examined. Sucrose phosphate synthase and fructose-1,6-bisphosphatase activities as well as the ratios of fructose-1,6-bisphosphate/fructose-6-phosphate and sucrose/starch indicated that cells grown at 27[deg]C/2200 [mu]mol m-2 s-1 appeared to exhibit a restriction in starch metabolism. In contrast, cells grown at 5[deg]C/150 [mu]mol m-2 s-1 appeared to exhibit a restriction in the sucrose metabolism based on decreased cytosolic fructose-1,6- bisphosphatase and sucrose phosphate synthase activities as well as a low sucrose/starch ratio. These metabolic restrictions may feed-back on photosynthetic electron transport and, thus, contribute to the observed PSII excitation pressure. We conclude that, although PSII excitation pressure may reflect redox regulation of photosynthetic acclimation to light and temperature in C. vulgaris, it cannot be considered the primary redox signal. Alternative metabolic sensing/signaling mechanisms are discussed.     

Anonymous nuclear DNA markers in the American oyster and their implications for the heterozygote deficiency phenomenon in marine bivalves

A puzzling population-genetic phenomenon widely reported in allozyme surveys of marine bivalves is the occurrence of heterozygote deficits relative to Hardy-Weinberg expectations. Possible explanations for this pattern are categorized with respect to whether the effects should be confined to protein-level assays or are genomically pervasive and expected to be registered in both protein- and DNA-level assays. Anonymous nuclear DNA markers from the American oyster were employed to reexamine the phenomenon. In assays based on the polymerase chain reaction (PCR), two DNA-level processes were encountered that can lead to artifactual genotypic scorings: (a) differential amplification of alleles at a target locus and (b) amplification from multiple paralogous loci. We describe symptoms of these complications and prescribe methods that should generally help to ameliorate them. When artifactual scorings at two anonymous DNA loci in the American oyster were corrected, Hardy-Weinberg deviations registered in preliminary population assays decreased to nonsignificant values. Implications of these findings for the heterozygote-deficit phenomenon in marine bivalves, and for the general development and use of PCR-based assays, are discussed.      

Effect of polyols on the post-thawing motility of pellet-frozen ram spermatozoa

The cryoprotective effects of polyols in the absence and presence of glycerol in Tris-glucose-egg yolk based diluents on the post-thawing motility and acrosome integrity of pellet-frozen ram spermatozoa were examined. Incorporation of adonitol or xylitol (low molecular weight polyols; LMWPs) in diluents improved motility of spermatozoa in the absence of glycerol with maximum motility at 0.3 M (26.9 vs 13.3% mean motile spermatozoa; P < 0.001). Five concentrations of adonitol (0, 150, 300, 450, 600 mM) were examined in diluents containing 5 concentrations of glycerol (0, 1.5, 3.0, 4.5, 6.0% v/v). There was an additive effect of incorporation of 1.5% v/v glycerol with up to 450 mM adonitol (P < 0.001), but at higher levels of glycerol the incorporation of adonitol was detrimental to motility. The acrosome integrity of spermatozoa in diluents containing 0, 150 and 300 mM adonitol was superior to those containing 450 and 600 mM adonitol (46.1 vs 35.1% mean intact acrosomes; P < 0.05). Among the high molecular weight polyols (HMWPs) examined, better recovery of spermatozoa was obtained in diluents containing sorbitol than mannitol or inositol (P < 0.001). Sorbitol or mannitol (300 mM) improved the motility of spermatozoa in diluents without glycerol (P < 0.001), but the incorporation of HMWPs was detrimental in diluents containing glycerol. All five polyols were examined in isotonic diluents containing 360:0, 300:55, 240:110, 180:165, 120:220mM (Tris:polyol; 360 mosmol) and 6.0% v/v glycerol. There was a linear decrease in motility and acrosome integrity of spermatozoa with increasing polyol concentration in the diluent (P < 0.001) except for inositol, which was not detrimental. We conclude that the polyols examined have a cryoprotective effect on pellet-frozen ram spermatozoa except for inositol. However, in our study, no combination of polyols and glycerol was superior in terms of post-thawing motility and acrosome integrity of spermatozoa to 6.0% v/v glycerol alone in Tris-glucose-egg yolk diluents.     

Changes in in vivo fluorescence quenching in rye and barley as a function of reduced PSII light harvesting antenna size

The relationship between the size of the light harvesting antenna to photosystem II (LHCII) and quenching of non-photochemical and dark level fluorescence was studied in wild-type rye (Secale cereale L. cv. Musketeer) and barley (Hordeum vulgare L. cv. Gunilla) as well as in the barley chlorophyll b-less chlorina F2 mutant (H. vulgare L. cv. Dornaria, chlorina-F2). Exposure for 10 min to an irradiance of 500 μmol m^?2 s^?1 resulted in a strong (0.71–0.73) non-photochemical (q_s) quenching of the fluorescence yield in wild-type (WT) material, while the barley chlorina F2-mutant was quenched to 75% of this level. Relaxation of q_s in darkness revealed a fast initial decay, related to relaxation of the high-energy-state dependent (q_E) part of q_s. Etiolated seedlings of rye and barley exposed to intermittent light (IML) for 36 cycles of 2 min light and 118 min darkness had suppressed Chl b and LHCII-production in both WT rye and barley, while the barley chlorina F2-mutant became totally devoid of all LHCII-polypeptides. It was found that the levels of q_s and q_s were similar in control grown barley chlorina F2 and IML-grown WT rye and barley, but q_s was reduced by 30 to 35% and q_s by 50 to 65%, respectively, as compared to control-grown. WT plants. No significant q_s could be detected in IML-grown barley chlorina F2. It is clear, from these changes in in vivo fluorescence quenching in rye and barley that a significant level of q_s is detectable even in the absence of LHCII. Only when the proximal antennae are totally absent, does q_E completely disappear. We conclude that the presence of LHCII is not an absolute requirement for q_E-quenching and suggest that distal as well as proximal antenna may contribute to q_E in vivo.     

Identifying historical and future global change drivers that place species recovery at risk

Ecosystem management in the face of global change requires understanding how co-occurring threats affect species and communities. Such an understanding allows for effective management strategies to be identified and implemented. An important component of this is differentiating between factors that are within (e.g. invasive predators) or outside (e.g. drought, large wildfires) of a local manager's control. In the global biodiversity hotspot of south-western Australia, small- and medium-sized mammal species are severely affected by anthropogenic threats and environmental disturbances, including invasive predators, fire, and declining rainfall. However, the relative importance of different drivers has not been quantified. We used data from a long-term monitoring program to fit Bayesian state-space models that estimated spatial and temporal changes in the relative abundance of four threatened mammal species: the woylie (Bettongia penicillata), chuditch (Dasyurus geoffroii), koomal (Trichosurus vulpecula) and quenda (Isoodon fusciventor). We then use Bayesian structural equation modelling to identify the direct and indirect drivers of population changes, and scenario analysis to forecast population responses to future environmental change. We found that habitat loss or conversion and reduced primary productivity (caused by rainfall declines) had greater effects on species' spatial and temporal population change than the range of fire and invasive predator (the red fox Vulpes vulpes) management actions observed in the study area. Scenario analysis revealed that a greater extent of severe fire and further rainfall declines predicted under climate change, operating in concert are likely to further reduce the abundance of these species, but may be mitigated partially by invasive predator control. Considering both historical and future drivers of population change is necessary to identify the factors that risk species recovery. Given that both anthropogenic pressures and environmental disturbances can undermine conservation efforts, managers must consider how the relative benefit of conservation actions will be shaped by ongoing global change.     

The interaction between coumarin drugs and DNA gyrase

The coumarin group of antibiotics have as their target the bacterial enzyme DNA gyrase. The drugs bind to the B subunit of gyrase and inhibit DNA supercoiling by blocking the ATPase activity. Recent data show that the binding site for the drugs lies within the N-terminal part of the B protein, and individual amino acids involved in coumarin interaction are being identified. The mode of inhibition of the gyrase ATPase reaction by coumarins is unlikely to be simple competitive inhibition, and the drugs may act by stabilizing a conformation of the enzyme with low affinity for ATP.     

Other cities,same problems.

London''s health care problems, particularly underfunding, are mirrored in other major cities in the United Kingdom and abroad. None has found the perfect solution, but the debates on the Tomlinson report provide an opportunity to review how to manage the three major areas of service provision, medical education, and research in London. Mr Robert Maxwell suggests that some aspects of the successful ambulatory care initiative in New York could be adapted by the capital''s primary care providers while the secondary services might learn from the rationalisation of specialist services in Paris.     

5'ETS rRNA processing facilitated by four small RNAs: U14, E3, U17, and U3.

The nucleolus, the compartment in which the large ribosomal RNA precursor (pre-rRNA) is synthesized, processed through a series of nucleolytic cleavages and modifications into the mature 18S, 5.8S, and 28S rRNAs, and assembled with proteins to form ribosomal subunits, also contains many small nucleolar RNAs (snoRNAs). We present evidence that the first processing event in mouse rRNA maturation, cleavage within the 5' external transcribed spacer, is facilitated by at least four snoRNAs: U14, U17(E1), and E3, as well as U3. These snoRNAs do not augment this processing by directing 2'-O-methylation of the pre-rRNA. A macromolecular complex in which this 5'ETS processing occurs may then function in the processing of 18S rRNA.     

Sources of variation in the reproductive performance of ewes inseminated with frozen-thawed ram semen by laparoscopy

Fertility data from 8 artificial insemination programs, involving more than 5000 ewes and 110 rams in 3 flocks, were analyzed to determine variation due to individual AI program and ram in the reproductive performance of ewes inseminated with frozen-thawed semen by laparoscopy. The semen had been previously frozen by commercial AI centers in either pellets or straws. Both AI program and individual ram affected the proportion of ewes pregnant and the number of fetuses per ewe inseminated, but not the number of fetuses per pregnant ewe. Semen samples from 97 of the rams used were analyzed on a Hamilton Thorn HTM 2000 image analyzer for sperm concentration, percentage of motile and progressively motile spermatozoa, mean progressive velocity, and mean linear index. The correlations between these traits and reproductive performance obtained after insemination were calculated. There was large variation in the quantity and quality of the frozen semen, but only the number of total and motile spermatozoa inseminated per ewe was correlated with fertility (0.25 and 0.26, respectively). Regression analysis showed that none of the traits measured were useful for predicting fertility.     

DNA topology: Topoisomerases keep it simple

The ability of type II DNA topoisomerases to perturb the equilibrium distributions of DNA topoisomers is a consequence of their ability to hydrolyse ATP. A sliding mechanism of topoisomerase action has been proposed to account for this phenomenon.