Faster evolution of highly conserved DNA in tropical plants

A faster rate of nuclear DNA evolution has recently been found for plants occupying warmer low latitudes relative to those in cooler high latitudes. That earlier study by our research group compared substitution rates within the variable internal transcribed spacer (ITS) region of the ribosomal gene complex amongst 45 congeneric species pairs, each member of which differed in their latitudinal distributions. To determine whether this rate differential might also occur within highly conserved DNA, we sequenced the 18S ribosomal gene in the same 45 pairs of plants. We found that the rate of evolution in 18S was 51% faster in the tropical plant species relative to their temperate sisters and that the substitution rate in 18S correlated positively with that in the more variable ITS. This result, with a gene coding for ribosomal structure, suggests that climatic influences on evolution extend to functionally important regions of the genome.     

Growth and Cellular Differentiation in the Wheat Coleoptile (Triticum vulgare L.): I. ESTIMATION OF CELL NUMBER, CELL VOLUME, AND CERTAIN NITROGENOUS CONSTITUENTS

The numbers and volumes of cells were determined for consecutivestages in the growth and development of the wheat coleoptile(var. ‘King II’) when grown at 25° C. in darknessfrom soon after germination to senescence. Cell expansion occurredthroughout growth and development up to 96 hours, and was accompaniedby cell division between 18–60 hours. Evidence is presentedthat suggests there are two phases of cell expansion concernedin coleoptile growth. Determinations were made at daily intervals from 24 to 120 hoursafter sowing of protein nitrogen, trichloroacetic acid solublenitrogen (TCA-sol. N), ribonucleic acid (RNA), and deoxyribonucleicacid (DNA) in the coleoptile, and the results expressed on aper-coleoptile and per-cell basis. The maximum rate of net proteinsynthesis took place during or after the cell-multiplicationphase of growth, depending on whether the results were expressedper coleoptile or per cell respectively. The ratio of proteinnitrogen to TCA-sol. N changed considerably during growth, from4·7 for young cells to 0·68 for mature cells. The fluctuations in the values for RNA and protein are consistentwith the template theory of protein synthesis and the DNA dataare discussed in relation to polyploidy in differentiated cells.No significant difference was found in the nucleotide compositionof RNA during the growth and development of the coleoptile.     

Effect of temperature and sex on growth patterns in nymphs of the mayfly Hexagenia hilineata in the laboratory

SUMMARY. Eggs collected from Hexagenia bilineata females were successfully reared in the laboratory at temperatures of 15, 20, 25 and 30°C. Eggs did not hatch at 10°C and although hatching was successful at 35°C, all nymphs at this temperature died while in early instars.
Survival of nymphs between the approximate size interval of 4–14 mm showed a significant decrease with increased temperatures. Nymphs at 15°C, however, generally did not survive transformation to the subaduit stage.
The growth pattern of individual nymphs was well described by a logistic curve at most temperatures. Furthermore, growth pattern was significantly affected by both temperature and sex.
Rate of development from oviposition to first emergence increased with increasing temperatures in a linear fashion between 15 and 30°C. The relationship was equally well described by a hyperbolic equation and a power-law equation. By extrapolation from the hyperbolic equation, the lower threshold temperature for development was estimated to be 10.1°C3.1°C. The degree (°C)-days required for development from oviposition to first emergence was calculated to be 2337 days with 95% confidence limits of 2045–2727 days under laboratory conditions.     

Adenovirus serotype determines association and localization of the large E1B tumor antigen with cellular tumor antigen p53 in transformed cells.

The distribution and stability of the cellular tumor antigen p53 were studied in baby rat kidney cells transformed by region E1 sequences of nononcogenic adenovirus (Ad) type 5 (Ad5) or oncogenic type 12 (Ad12). In transformed cells expressing the large E1B T antigen of Ad5, p53 was associated with this T antigen. The complexed proteins were concentrated in a cytoplasmic body, which has been shown to consist of a cluster of 8-nm filaments (A. Zantema et al., Virology 142:44-58, 1985). In transformed cells expressing the E1B region of Ad12, however, no association between the viral large T antigen and p53 was detectable. In the latter case, both proteins were found almost exclusively in the nucleus. The stability of p53 in both Ad5- and Ad12-transformed cells was increased relative to that in primary cells or cells immortalized by the E1A region only. Thus, the increased stability of p53 in Ad-transformed cells is not caused by association with a viral T antigen, but it correlates with expression of E1B and with morphological transformation.     

Male mating success in an aquatically mating pinniped, the harbour seal (Phoca vitulina), assessed by microsatellite DNA markers

Similar to many other pinniped species, harbour seals ( Phoca vitulina ) mate exclusively at sea. Here we present the first attempt to measure male mating success in an aquatically mating pinniped. Male mating success was estimated by paternity analysis in two cohorts of pups born at Sable Island, Nova Scotia, Canada, using microsatellite DNA markers. The genotypes of 275 pups born in 1994 and 1995 were compared to those of 90 candidate males at six microsatellite loci using a likelihood approach to resolve paternity. Paternity could be assigned for two, 22, 40 and 85 pups at confidence levels of 95, 80, 65 and 50%, respectively. Most successful males were assigned the paternity of a single offspring, suggesting a low variance in male mating success relative to most pinniped species. The proportion of paternal half sibs within cohorts and between maternally related sibs estimated by maximum likelihood were not significantly different from zero. It is thus unlikely that most offspring were sired by a small number of highly successful unsampled males, and that female harbour seals do not usually exhibit fidelity to the same male in sequential breeding seasons. A low level of polygyny in Sable Island harbour seals is consistent with predictions based on their breeding ecology, as females are highly mobile and widely dispersed in the aquatic mating environment at Sable Island.     

Experimentally increased soil temperature causes release of nitrogen at a boreal forest catchment in southern Norway

Boreal forest ecosystems are sensitive to global warming, caused by increasing emissions of CO₂ and other greenhouse gases. Assessment of the biological response to future climate change is based mainly on large-scale models. Whole-ecosystem experiments provide one of the few available tools by which ecosystem response can be measured and with which global models can be evaluated. Boreal ecosystem response to global change may be manifest by alterations in nitrogen (N) dynamics, as N is often the growth limiting nutrient. The CLIMEX (Climate Change Experiment) project entails catchment-scale manipulations of CO₂ (to 560 ppmv) and temperature (by + 3 to + 5 °C) to whole forest ecosystems in southern Norway. Soil temperature is increased at 400-m² EGIL catchment by means of electric cables placed on the soil surface. Soil warming at EGIL catchment caused an increase in nitrate and ammonium concentrations in runoff in the first year of treatment. We hypothesize that higher temperature increased N release by mineralization. Whether these responses are only transient will be shown by additional years' treatment.     

Serological detection of ryegrass mosaic virus and ryegrass seed-borne virus

Ryegrass mosaic virus (RMV) was reliably detected in both perennial (S24) and Italian (S22) ryegrass, by enzyme-linked immunosorbent assay (ELISA) when plants had been infected for 8 wk. ELISA detected more infections in field-grown perennial ryegrass cv. Premo than either visual assessment or electron microscopy. However, with plants of Italian ryegrass cultivars only recently infected with RMV, positive reactions were more difficult to separate from the reactions of RMV-free plants, which varied considerably with cultivar, some giving high absorbance values. Immunosorbent electron microscopy showed that the RMV antiserum also contained antibodies to ryegrass seed-borne virus (RGSV), suggesting that these high values were caused by RGSV infection in the material tested.