Cytopathology of Lettuce Mosaic Virus-infected Lettuce Seeds and Seedlings

The ultrastructure of lettuce mosaic potyvirus (LMV)-infected lettuce seeds and seedlings was studied by transmission electron microscopy. Conventional thin-section electron microscopy and immunogold cytochemistry were both successfully employed to study the location of LMV in embryonic and non-embryonic seed parts. LMV particle aggregates and cytoplasmic “pinwheel” inclusions characteristic of potyviruses were observed throughout the embryonic tissues (radicle, hypocotyl and cotyledon) of infected lettuce seeds and seedlings, and also in the non-embryonic endosperm layer. LMV particles, but not inclusions, were also located in the non-embryonic pericarp layer.     

Hydantoin based inhibitors of MMP13—Discovery of AZD6605

Piperidine ether and aryl piperazine hydantoins are reported as potent inhibitors of MMP13. A medicinal chemistry campaign focused on replacing the reverse hydroxamate zinc binding group associated with historical inhibitors with a hydantoin zinc binding group then optimising MMP13 potency, solubility and DMPK properties whilst maintaining good selectivity over MMP14. A number of high quality candidates were progressed and following rat and dog safety evaluation, AZD6605 (3m) was identified as a candidate drug.     

Effects of harvest,culture, and climate on trends in size of horn-like structures in trophy ungulates

Hunting remains the cornerstone of the North American model of wildlife conservation and management. Nevertheless, research has indicated the potential for hunting to adversely influence size of horn-like structures of some ungulates. In polygynous ungulates, mating success of males is strongly correlated with body size and size of horn-like structures; consequently, sexual selection has favored the development of large horns and antlers. Horn-like structures are biologically important and are of great cultural interest, both of which highlight the need to identify long-term trends in size of those structures, and understand the underlying mechanisms responsible for such trends. We evaluated trends in horn and antler size of trophy males (individuals exhibiting exceptionally large horns or antlers) recorded from 1900 to 2008 in Records of North American Big Game, which comprised >22,000 records among 25 trophy categories encompassing the geographic extent of species occupying North America. The long-term and broad-scale nature of those data neutralized localized effects of climate and population dynamics, making it possible to detect meaningful changes in size of horn-like structures among trophy males over the past century; however, ages of individual specimens were not available, which prevented us from evaluating age-class specific changes in size. Therefore, we used a weight-of-evidence approach based on differences among trophy categories in life-history characteristics, geographic distribution, morphological attributes, and harvest regimes to discriminate among competing hypotheses for explaining long-term trends in horn and antler size of trophy ungulates, and provide directions for future research. These hypotheses were young male age structure caused by intensive harvest of males (H1), genetic change as a result of selective male harvest (H2), a sociological effect (H3), effects of climate (H4), and habitat alteration (H5). Although the number of entries per decade has increased for most trophy categories, trends in size of horn-like structures were negative and significant for 11 of 17 antlered categories and 3 of 8 horned categories. Mean predicted declines during 1950–2008 were 1.87% and 0.68% for categories of trophy antlers and horns, respectively. Our results were not consistent with a sociological effect (H3), nutritional limitation imposed by climate (H4), or habitat alteration (H5) as potential explanations for long-term trends in size of trophies. In contrast, our results were consistent with a harvest-based explanation. Two of the 3 species that experienced the most conservative harvest regimes in North America (i.e., bighorn sheep [Ovis canadensis] and bison [Bison bison]) did not exhibit a significant, long-term trend in horn size. In addition, horn size of pronghorn (Antilocapra americana), which are capable of attaining peak horn size by 2–3 years of age, increased significantly over the past century. Both of those results provide support for the intensive-harvest hypothesis, which predicts that harvest of males has gradually shifted age structure towards younger, and thus smaller, males. The absence of a significant trend for mountain goats (Oreamnos americanus), which are difficult to accurately judge size of horns in the field, provided some support for the selective-harvest hypothesis. One other prediction that followed from the selective-harvest hypothesis was not supported; horned game were not more susceptible to reductions in size. A harvest-induced reduction in age structure can increase the number of males that are harvested prior to attaining peak horn or antler size, whereas genetic change imposed by selective harvest may be less likely to occur in free-ranging populations when other factors, such as age and nutrition, can override genetic potential for size. Long-term trends in the size of trophy horn-like structures provide the incentive to evaluate the appropriateness of the current harvest paradigm, wherein harvest is focused largely on males; although the lack of information on age of specimens prevented us from rigorously differentiating among causal mechanisms. Disentangling potential mechanisms underpinning long-term trends in horn and antler size is a daunting task, but one that is worthy of additional research focused on elucidating the relative influence of nutrition and effects (both demographic and genetic) of harvest. © 2013 The Wildlife Society.     

Dioxathiadiaza-heteropentalenes. New Photosystem-I electron acceptors

The redox properties of some dioxathiadiaza-heteropentalenes have been studied by pulse radiolysis and cyclic voltammetry. The midpoint potential at pH 7 for reduction of this class of compounds to the corresponding anion radical is comparable with the first reduction potential of the bipyridinium herbicides. The heteropentalenes act as Photosystem-I electron acceptors at concentrations of the order of 1 · 10^?6 M. The herbicidal properties of the heteropentalenes are similar to those of the bipyridinium herbicides.     

Modification of the apparent redox reaction between cytochrome f and the rieske iron-sulfur protein

We have investigated the role of cytochrome f and the Rieske FeS protein in spinach chloroplasts using the quinone analogue 5-(n-undecyl)-6-hydroxy-4,7-dioxobenzothiazole (UHDBT). UHDBT inhibits electron transport at two different sites in spinach chloroplasts. Fluorescence yield measurements monitoring the redox state of Q, the first stable primary acceptor of Photosystem II, and polarographic measurements of electron transport show that at low concentrations UHDBT inhibits near Q. At higher concentrations UHDBT inhibits at a second site. Electron transfer from durohydroquinone to methyl viologen is inhibited (50% inhibition at 21 μM) but not the reaction dichlorophenolindophenol to methyl viologen. Spectroscopic measurements of the kinetics of cytochrome f show that UHDBT inhibits the dark reduction rate of the cytochrome following a 100 ms flash (50% inhibition at 15 μM). By contrast, the oxidation kinetics of cytochrome f following a single-turnover flash are altered little by UHDBT; the initial rates are indistinguishable, and the half-time increases from 220 μs in the control to 285 μs in the presence of 15 μM UHDBT, largely because the extent of the cytochrome f oxidation is enhanced 1.4-fold in the presence of the inhibitor. In a single-turnover flash in the absence of UHDBT, we observe 38–48% of the total cytochrome f turning over, while in the presence of UHDBT we observe 60–69% of the cytochrome turning over. We interpret these results in terms of a linear rapid donor pool to Photosystem I, FeS → cytochrome f → plastocyanin → P-700, in which UHDBT inhibits by interacting with the Rieske FeS center. We conclude that the enhanced extent of cytochrome f oxidation in the presence of UHDBT is due to the removal of the Rieske FeS center from the rapid donor pool. As a consequence, removal of a single electron from the pool results in a greater cytochrome f oxidation. These results indicate that the Rieske FeS center and cytochrome f equilibrate in a time period comparable to the oxidation time of the cytochrome.     

The role of the Rieske iron-sulfur center as the electron donor to ferricytochrome c2 in Rhodopseudomonas sphaeroides

The Rieske iron-sulfur center in the photosynthetic bacterium Rhodopseudomonas sphaeroides appears to be the direct electron donor to ferricytochrome c₂, reducing the cytochrome on a submillisecond timescale which is slower than the rapid phase of cytochrome oxidation ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{3–5 μ}\text{s}$). The reduction of the ferricytochrome by the Rieske center is inhibited by 5-n-undecyl-6-hydroxy-4,7-dioxobenzothiazole (UHDBT) but not by antimycin. The slower (1–2 ms) antimycin-sensitive phase of ferricytochrome c₂ reduction, attributed to a specific ubiquinone-10 molecule (Q_z), and the associated carotenoid spectral response to membrane potential formation are also inhibited by UHDBT. Since the light-induced oxidation of the Rieske center is only observed in the presence of antimycin, it seems likely that the reduced form of Q_z (Q_zH₂) reduces the Rieske center in an antimycin-sensitive reaction. From the extent of the UHDBT-sensitive ferricytochrome c₂ reduction we estimate that there are 0.7 Rieske iron-sulfur centers per reaction center.UHDBT shifts the EPR derivative absorption spectrum of the Rieske center from g_y 1.90 to g_y 1.89, and shifts the E_m,7 from 280 to 350 mV. While this latter shift may account for the subsequent failure of the iron-sulfur center to reduce ferricytochrome c₂, it is not clear how this can explain the other effects of the inhibitor, such as the prevention of cytochrome b reduction and the elimination of the uptake of H⁺_II; these may reflect additional sites of action of the inhibitor.     

Genetic effects of habitat contraction on Lumholtz's tree-kangaroo (Dendrolagus lumholtzi) in the Australian Wet Tropics

Lumholtz's tree-kangaroo (Dendrolaguslumholtzi) is one of two species oftree-kangaroo resident in the tropicalrainforests of north-eastern Australia. Thespecies is confined to the Wet Tropics region,with its distribution centred on the AthertonTablelands. While D. lumholtzi wasexposed to periodic large-scale climaticfluctuations during the Quaternary that haveeffectively acted as natural fragmentationevents, the species is currently under pressurefrom anthropogenic disturbance and habitatfragmentation. This study aimed to assess thelevel of genetic diversity in D.lumholtzi by examining hypervariablemicrosatellite loci and the control region ofmitochondrial DNA (mtDNA) in 21 individualsfrom a single 20 ha forest fragment, and from afurther 24 animals collected throughout theAtherton Tablelands. Results suggest that D. lumholtzi has relatively low levels ofgenetic diversity which is uniformlydistributed throughout the Atherton Tablelands;a pattern congruent with data from many othervertebrates endemic to the Australian WetTropics. It is suggested that Pleistoceneclimatic fluctuations, which resulted inlarge-scale rainforest contractions, haveimposed an ancient population bottleneck on theancestral D. lumholtzi population. Theapparent over-riding influence of thesenatural, historical effects on the geneticstructure of D. lumholtzi populations,will complicate attempts to assess the geneticimpact of current anthropogenic habitat lossand fragmentation.