Measurement of Temperature and Humidity in Tobacco Plots in Rhodesia

Small nickel resistance thermometers were tested in variousanti-radiation screens over bare sandy soil in Southern Rhodesia.Satisfactory results were obtained only when the thermometerswere aspirated in small chromed metal shields, based on thedesign of the Mark 3 Assmann psychrometer. The aspirated unitswere compared with an Assmann, at various heights within tobaccoplots during a range of whether conditions, and grave satisfactoryresults when used for continuous periods of several months.Some results are presented illustrating the vertical distributionof temperature and humidity within tobacco plots at differentstages of growth. When plants were small, temperature and humiditygradients appeared to be similar to those that might be expectedover open ground. Later the pattern resembled that of a cropof medium ground cover and density.     

Support of benthic invertebrates by detrital resources and current autochthonous primary production: results from a whole-lake 13C addition

1. Secondary production of benthic invertebrates in lakes is supported by current autochthonous primary production, and by detritus derived from a combination of terrestrial inputs and old autochthonous production from prior seasons. We quantified the importance of these two resources for the dominant benthic insects in Crampton Lake, a 26 ha, clear-water system.
2. Daily additions of NaH¹³CO₃ to the lake caused an increase in the stable carbon isotope ratios ( δ ¹³C) of the current primary production of phytoplankton and periphyton. We measured the response of four insect groups (taxon-depth combinations) to this manipulation, quantifying their current autochthony (% reliance on current autochthonous primary production) by fitting dynamic mixing models to time series of insect δ ¹³C.
3. The δ ¹³C of all four groups increased in response to the manipulation, although the magnitude of response differed by taxon and by depth, indicating differences in current autochthony. Odonate larvae (Libellulidae and Corduliidae) collected at 1.5 m depth derived 75% of their C from current autochthonous primary production. Chironomid larvae collected at 1.5, 3.5 and 10 m depths derived, respectively, 43%, 39% and 17% of their C from current autochthonous primary production.
4. Both taxon-specific diet preferences and depth-specific differences in resource availability may contribute to differences in current autochthony. Our results demonstrate significant but incomplete support of insect production by current autochthony, and indicate that allochthonous inputs and old autochthonous detritus support a substantial fraction (25–83%) of insect production.     

<Emphasis Type="Italic">Pichia stipitis</Emphasis> xylose reductase helps detoxifying lignocellulosic hydrolysate by reducing 5-hydroxymethyl-furfural (HMF)

Background  

Pichia stipitis xylose reductase (Ps-XR) has been used to design Saccharomyces cerevisiae strains that are able to ferment xylose. One example is the industrial S. cerevisiae xylose-consuming strain TMB3400, which was constructed by expression of P. stipitis xylose reductase and xylitol dehydrogenase and overexpression of endogenous xylulose kinase in the industrial S. cerevisiae strain USM21.     

Powdery mildew of tobacco (Erysiphe cichoracearum DC.)

In water culture experiments, tobacco plants of Hicks variety were supplied with factorial combinations of high and low concentrations of nitrogen, phosphorus and potassium. Incidence of powdery mildew and growth and chemical composition of infected and healthy plants were compared.
There was more disease when all elements were supplied at the higher of two concentrations, but the increase in infection was less than the increase in growth. Plants grown in media containing a low ratio of potassium to nitrogen produced the least susceptible leaves; their disease indices were up to 30 times less than those of plants that received the full nutrient treatment. Potassium-deficient leaves had thinner cell walls, larger water content, smaller sugar and potassium contents, and greater amino nitrogen and magnesium contents, compared with those of plants grown in any of the other media. The possible relation between these characteristics and susceptibility to Erysiphe cichoracearum DC. are discussed.     

Reduced natural selection associated with low recombination in Drosophila melanogaster

Synonymous codons are not used equally in many organisms, and the extent of codon bias varies among loci. Earlier studies have suggested that more highly expressed loci in Drosophila melanogaster are more biased, consistent with findings from several prokaryotes and unicellular eukaryotes that codon bias is partly due to natural selection for translational efficiency. We link this model of varying selection intensity to the population-genetics prediction that the effectiveness of natural selection is decreased under reduced recombination. In analyses of 385 D. melanogaster loci, we find that codon bias is reduced in regions of low recombination (i.e., near centromeres and telomeres and on the fourth chromosome). The effect does not appear to be a linear function of recombination rate; rather, it seems limited to regions with the very lowest levels of recombination. The large majority of the genome apparently experiences recombination at a sufficiently high rate for effective natural selection against suboptimal codons. These findings support models of the Hill-Robertson effect and genetic hitchhiking and are largely consistent with multiple reports of low levels of DNA sequence variation in regions of low recombination.      

Kappa-chain constant-region gene sequences in genus Rattus: coding regions are diverging more rapidly than noncoding regions

We have determined the nucleotide sequence of a 1,200-base pair (bp) genomic fragment that includes the kappa-chain constant-region gene (C kappa) from two species of native Australian rodents, Rattus leucopus cooktownensis and Rattus colletti. Comparison of these sequences with each other and with other rodent C kappa genes shows three surprising features. First, the coding regions are diverging at a rate severalfold higher than that of the nearby noncoding regions. Second, replacement changes within the coding region are accumulating at a rate at least as great as that of silent changes. Third, most of the amino acid replacements are localized in one region of the C kappa domain--namely, the carboxy-terminal "bends" in the alpha-carbon backbone. These three features have previously been described from comparisons of the two allelic forms of C kappa genes in R. norvegicus. These data imply the existence of considerable evolutionary constraints on the noncoding regions (based on as yet undetermined functions) or powerful positive selection to diversify a portion of the constant-region domain (whose physiological significance is not known). These surprising features of C kappa evolution appear to be characteristic only of closely related C kappa genes, since comparison of rodent with human sequences shows the expected greater conservation of coding regions, as well as a predominance of silent nucleotide substitutions within the coding regions.