Climate change cannot be entirely responsible for soil carbon loss observed in England and Wales, 1978–2003

We present results from modelling studies, which suggest that, at most, only about 10–20% of recently observed soil carbon losses in England and Wales could possibly be attributable to climate warming. Further, we present reasons why the actual losses of SOC from organic soils in England and Wales might be lower than those reported.     

Multidecadal to millennial-scale shifts in drought conditions on the Canadian prairies over the past six millennia: implications for future drought assessment

Three high-resolution climatic reconstructions, based on diatom analyses from lake sediment cores from the Canadian prairies, show that shifts in drought conditions have prevailed on centennial to millennial time scales for at least the past six millennia. These shifts in mean aridity exhibit broad regional synchrony, with particularly pronounced shifts at all sites between ∼1700–2000 cal. yr bp and ∼3600–3900 cal. yr bp , as well as at ∼5400–5500 cal. yr bp for the two sites which extend back to at least 6000 cal. yr bp . The two Saskatchewan lakes exhibited significant coherence in both the timing and direction of these shifts, whereas inferred changes at the westernmost site in Alberta were significantly correlated to the Saskatchewan sites, but opposite in sign, and exhibited more high-frequency variation on the scale of centuries. The mechanisms behind these abrupt shifts in aridity are poorly understood, but may be linked to changes in oceanic–atmospheric interactions that influence the mean position of the jetstream and the associated storm tracks. Natural shifts in mean climatic conditions may accelerate with increasing carbon dioxide levels intensifying the likelihood of extreme droughts in North American prairies.     

Responses to olfactory and visual cues by over-wintered and summer generations of the pollen beetle, Meligethes aeneus

Abstract.  Behavioural responses to odours of oilseed rape in bud and flower stage and to green and yellow colours are studied for the two main phenological stages of pollen beetles, Meligethes aeneus , a major pest of oilseed rape, Brassica napus . Over-wintered individuals oviposit in buds of oilseed rape. Adults of the new generation (i.e. the summer generation) feed on flowers of different plant species before over wintering. In olfactometer experiments, the over-wintered beetles display a higher preference for odour of oilseed rape at the bud stage compared with the summer generation, both with and without colour stimuli. Flower odours are preferred in combination with yellow colour. Colour stimuli presented alone do not affect the behaviour. The summer generation beetles respond to both bud and flower odour. Adding colour stimuli changes the summer generations preference towards yellow and flower odour.     

Muscarone: An Enigma Resolved?

WITH the exception of muscarone, the potencies of the optical enantiomers of stimulants of the cholinergic post-ganglionic parasympathetic (muscarinic) nervous junction differ greatly, typically by about 200:1 (refs. 1 and 2). Furthermore, the absolute configuration of all the more potent enantiomers is the same³, that of L(+)-muscarine. The ratio of activities for muscarone, however, is only about 3:1 (refs. 1 and 2) and the more potent enantiomer is the D(?). Various rationalizations of this exception have been proposed in the absence of any conformational information. We have determined the conformation of muscarone in crystals of the iodide and suggest an alternative explanation of the activities of the enantiomers which fits the proposed structure-activity relationships of muscarinic^{3, 4} and nicotinic⁵ agonists of cholinergic nervous systems.     

Mechanism of Mitochondrial Mutation in Yeast

THE yeast Saccharomyces cerevisiae can mutate to the respiratory-incompetent petite colony form. The mutation is probably caused by damage to, or loss of, the yeast's mitochondrial DNA, for petite mutants often lack mitochondrial DNA, possess it in abnormal amounts or with abnormal buoyant density¹. Some of the agents, such as acrifiavine or ethidium bromide, which induce the petite mutation interfere with mitochondrial DNA synthesis^2,3 whereas ethidium bromide also causes or permits degradation of Saccharomyces cerevisiae mitochondrial DNA^2,3. We have observed that nalidixate (50 µg/ml.), an inhibitor of DNA synthesis, can prevent or delay petite mutation induced by ethidium bromide⁴. A similar effect has been observed by Hollenberg and Borst using a higher nalidixate concentration⁵. We have investigated the mechanism of this effect. A diploid prototrophic strain of Saccharomyces cerevisiae (NCYC 239) was used throughout.     

Defective Gene Product in <Emphasis Type="Italic">dna</Emphasis>F Mutant of <Emphasis Type="Italic">Escherichia coli</Emphasis>

The dnaF mutant of Escherichia coli has been shown to contain very low ribonucleoside diphosphate reductase activity. The B1 sub unit of the reductase is heat-sensitive in the mutant.     

The Adaptation of Enzymes to Pressure II. A Comparison of Muscle Pyruvate Kinases from Surface and Midwater Fishes with the Homologous Enzyme from an Off-Shore Benthic Species

SYNOPSIS. Pyruvate kinase (PK) maximum catalytic rate is dramaticallydecelerated by increasing hydrostatic pressure. In four differentspecies inhabiting different portions of the water column, musclepyruvate kinase displays (1) a reduction in the volume changeof activation, V*. a t higher temperatures, (2) a pH independenceof V*, and (3) a general increase in the activation energy atincreased pressures. Although shared by the four different pyruvatekinases examined, none of these characteristics is criticallyinvolved in the regulation of PK catalysis. In contrast, pressureeffects on another set of characteristics, all vitally importantto control of PK catalytic function, depend upon the speciesorigin of the enzyme. In the case of the rainbow trout, Salmogairdneri, high pressure dramatically reduces pyruvate kinaseaffinities for the two substrates (PEP and ADP), the cationiccofactor (Mg²⁺), and the negative modulator (ATP). The homologousmuscle enzyme from Oligoplites mundus, another surface dwellingspecies, displays similar responses to pressure. On the otherhand, muscle PK affinities for the same key regulatory ligandsare much less pressure sensitive in the abyssal rattail fishes(Coryphaenoides sp.) and are essentially pressure independentin a vertically migrating midwater sea bass, Ectreposebastesimus. In these latter two species, PK catalytic rates underprobable physiological conditions are determined largely bythese kinetic properties rather than by energy-volume parameters.     

The Adaptation of Enzymes to Pressure I. A Comparison of Trout Liver Fructose Diphosphatase with the Homologous Enzyme from an Off-Shore Benthic Fish

SYNOPSIS. At low temperature (3°C), in the absence of substrateand cofactor, trout liver fructose diphosphatase (FDPase) isinactivated by exposures to relatively low pressures. FDP andMg²⁺ protect against this inactivation; hence, maximum catalysisat pH 7.5 is pressure insensitive, while at more alkaline pH,it is markedly accelerated by pressure. The volume change ofactivation, V*, at saturating FDP and Mg²⁺ concentrations isabout –40 cm₃/mole. The apparent Km for FDP and the Kafor Mg²⁺ are markedly increased by pressure. At low FDP or Mg²⁺levels these kinetic properties outweigh V* in determining thereaction rate; hence, under these conditions, piessure retardscatalysis. Similarly, the K₄ for AMP is notably pressure sensitive.Comparable effects of pressure on the kinetic constants forliver FDPase from benthic Corypliaenoides are much less pronounced,suggesting that in these off-shore species enzyme-substrate,enzyme-cofactor, and enzyme-modulator interactions have beentailored through evolution for pressure independent catalyticfunction.     

The cheeks of ornithischian dinosaurs

Except in a couple of very primitive genera the cheek teeth of ornithischians are inset with a lateral space that was roofed by the overhanging maxilla and floored by the massive dentary. This lateral space was delimited by cheeks and the mouth was small. The cheek muscles were not homologous to the Musculus buccinatoris of mammals, but the function was the same, to prevent the loss of food from the sides of the jaws during chewing. The evolution of self-sharpening cheek teeth and of cheeks enabled ornithischians to eat much more resistant plant material and resulted in ornithischians replacing prosauropods as the 'small to medium sized' terrestrial herbivores (up to 10 m).     

The Structure and Development of the Thallus in the British Species of Gelidium and Pterocladia

The apical structure and the development of the thalli of allthe British species of Gelidium and Pterocladia have been investigated;the development of G. pulchellum is described in detail. Eachaxis is terminated by one or more apical cells, which by theirsegmentation form the tissues of the thallus. An axial filamentis distinct for a short distance behind each apical cell, butsecondary pit-connexions develop rapidly so that in sectionthe mature axis has the appearance of a multi-axial structure. Lateral branches of the frond develop by the segmentation ofthe lateral branch apical cells, which are formed by the transformationof superficial cortical cells, either in the meristematic ormature parts of the axes. The extreme variability of externalappearance is due principally to the indeterminate origin ofall lateral branches. The thallus in the British species of Gelidium and Pterocladiaconsists of erect fronds borne on creeping axes. The relativeproportions of the frond and creeping axes in various speciesand their survival through adverse conditions are discussed.