Height convergence in response to neighbour growth: genotypic differences in the stoloniferous plant Potentilla reptans

Using a new experimental set up, the way in which height growth of stoloniferous plants is adjusted to that of their neighbours, as well as differences between genotypes in their ability to keep up with neighbour height growth were tested. Five Potentilla reptans genotypes inherently differing in petiole length were subjected to three experimental light gradients, involving light intensity and red : far-red ratio. Each plant was placed in a vertically adjustable cylinder of green foil, and the treatments differed in the speed of cylinder height increase and final height. Total weight of plants decreased from the 'Slow' to the 'Fast' treatment, while petiole length increased. Leaves reaching the top of the cylinder stopped petiole elongation, resulting in similar final heights for all genotypes in the 'Slow' treatment. In the 'Fast' treatment only the fastest-growing genotype maintained its position in the top of the cylinder and genotypes differed strongly in final height within the cylinders. Plants adjust their height growth to that of the surrounding vegetation, leading to height convergence in short light gradients that slowly increase. These adjustments and genotypic differences in ability to keep up with fast-growing neighbours can influence the outcome of competition for light.     

Coordinate induction of PPAR alpha and SREBP2 in multifunctional protein 2 deficient mice

Mice with inactivation of the D-specific multifunctional protein 2 (MFP2), a crucial enzyme of peroxisomal beta-oxidation, develop multiple pathologies in diverse tissues already starting in the postnatal period. Gene expression profiling performed on liver of 2-day-old pups revealed up-regulation of PPAR alpha responsive genes in knockout mice. Surprisingly, also genes involved in cholesterol biosynthesis were markedly induced. Real-time PCR confirmed the induction of PPAR alpha target genes and of HMGCR and SREBP2, both involved in cholesterol synthesis, in lactating and in adult MFP2 knockout mice. In accordance, the rate of cholesterol biosynthesis was significantly increased in liver of knockout mice but the hepatic cholesterol concentration was unaltered. In MFP2/PPAR alpha double knockout mice, up-regulations of SREBP2 and HMGCR were markedly attenuated. These data demonstrate a tight interrelationship between induction of PPAR alpha by endogenous ligands and up-regulation of genes of cholesterol biosynthesis through increased expression of SREBP2.     

米心水青冈幼苗对光照和养分的响应

在模拟郁闭林下(L1,大约1%～2%的全日照)、林窗(L2,大约18%的全日照)、开阔地(L3,全日照)3个光照水平和每个光照水平下进行施肥(F1)和不施肥(F0)对照的6个实验处理条件下,研究了 2年龄米心水青冈(Fagus engleriana Seem)幼苗在随后的两个生长季里的生长对光照和土壤养分的响应.结果显示:光照和养分对幼苗高度、基径和生物量有显著的影响.经过两个生长季,L1处理下幼苗高度增量极显著地小于L2和L3处理下幼苗高度增量.L1处理下基径和生物量的增量在处理当年秋就极显著地小于L2和L3处理下的增量,并在第二年差异继续扩大.L2和L3处理下的幼苗间的生长没有显著差异.施肥明显地促进了L2和L3处理下的幼苗的生长,但对L1处理下的幼苗没有明显的作用.这些结果说明,虽然2年龄米心水青冈幼苗能够在林下的弱光条件下生存,但生长受到了极大的抑制.幼苗在林窗的中等光照条件下能够与在开阔地全日照条件下生长的一样好或更好,这与许多耐阴的落叶树的响应一样.在比林内光照强度较高的条件下施肥或较高的土壤养分才对米心水青冈幼苗的生长和生存起作用.     

Expression of a mouse selenocysteine lyase in Brassica juncea chloroplasts affects selenium tolerance and accumulation

Selenium is an essential nutrient for many organisms, as part of certain selenoproteins. However, selenium is toxic at high levels, which is thought to be due to non-specific replacement of cysteine by selenocysteine leading to disruption of protein function. In an attempt to prevent non-specific incorporation of selenocysteine into proteins and to possibly enhance plant selenium tolerance and accumulation, a mouse selenocysteine lyase was expressed in Brassica juncea (Indian mustard) chloroplasts, the site of selenocysteine synthesis. This selenocysteine lyase specifically breaks down selenocysteine into elemental selenium and alanine. The transgenic cpSL plants showed normal growth under standard conditions. Selenocysteine lyase activity in the cpSL transgenics was up to 6-fold higher than in wild-type plants. The cpSL transgenics contained up to 40% less selenium in protein compared to wild-type plants, indicating that Se flow in the plant was successfully redirected. Surprisingly, the selenium tolerance of the transgenic cpSL plants was reduced, perhaps due to interference of produced elemental selenium with chloroplastic sulphur metabolism. Shoot selenium levels were enhanced up to 50% in the cpSL transgenics, but only during the seedling stage.     

Light partitioning among species and species replacement in early successional grasslands

Abstract. We studied canopy structure, shoot architecture and light harvesting efficiencies of the species (photon flux captured per unit above‐ground plant mass) in a series of exclosures of different age (up to 4.5 yr) in originally heavily grazed grassland in N Japan.Vegetation height and Leaf Area Index (LAI) increased in the series and Zoysia japonica, the dominant in the beginning, was replaced by the much taller Miscanthus sinensis. We showed how this displacement in dominance can be explained by inherent constraints on the above‐ground architecture of these two species. In all stands light capture of plants increased with their above‐ground biomass but taller species were not necessarily more efficient in light harvesting. Some subordinate species grew disproportionally large leaf areas and persisted in the shady undergrowth. Some other species first grew taller and managed to stay in the better‐lit parts of the canopy, but ultimately failed to match the height growth of their neighbours in this early successional series. Their light harvesting efficiencies declined and this probably led to their exclusion. By contrast, species that maintained their position high in the canopy managed to persist in the vegetation despite their relatively low light harvesting efficiencies. In the tallest stands ‘later successional’ species had higher light harvesting efficiencies for the same plant height than ‘early successional’ species which was mostly the result of the greater area to mass ratio (specific leaf area, SLA) of their leaves. This shows how plant stature, plasticity in above‐ground biomass partitioning, and architectural constraints determine the ability of plants to efficiently capture light, which helps to explain species replacement in this early successional series.     

Identifying Predictors of Activity Based Anorexia Susceptibility in Diverse Genetic Rodent Populations

Animal studies are very useful in detection of early disease indicators and in unravelling the pathophysiological processes underlying core psychiatric disorder phenotypes. Early indicators are critical for preventive and efficient treatment of progressive psychiatric disorders like anorexia nervosa. Comparable to physical hyperactivity observed in anorexia nervosa patients, in the activity-based anorexia rodent model, mice and rats express paradoxical high voluntary wheel running activity levels when food restricted. Eleven inbred mouse strains and outbred Wistar WU rats were exposed to the activity-based anorexia model in search of identifying susceptibility predictors. Body weight, food intake and wheel running activity levels of each individual mouse and rat were measured. Mouse strains and rats with high wheel running activity levels during food restriction exhibited accelerated body weight loss. Linear mixed models for repeated measures analysis showed that baseline wheel running activity levels preceding the scheduled food restriction phase strongly predicted activity-based anorexia susceptibility (mice: Beta  =  −0.0158 (±0.003 SE), P<0.0001; rats: Beta  =  −0.0242 (±0.004 SE), P<0.0001) compared to other baseline parameters. These results suggest that physical activity levels play an important role in activity-based anorexia susceptibility in different rodent species with genetically diverse background. These findings support previous retrospective studies on physical activity levels in anorexia nervosa patients and indicate that pre-morbid physical activity levels could reflect an early indicator for disease severity.     

Hyper-recombination in dam mutants of Escherichia coli K-12

Summary F-prime heterogenotes of dam-3 bacteria segregate F-prime homogenotes at a frequency 30–200 times higher than the isogenic dam ⁺ strain. A hyperrecombination mutant which shows increased recombination between chromosomal duplications was characterized as a dam mutant. The dam-3 allele causes a reduction in linkage of proximal unselected markers in transconjugants and increases the recombination frequency between a pair of closely linked markers. It is concluded that dam mutations confer a hyperrecombination phenotype to the cell.     

Studies on mutagenesis and repair induced by platinum analogs

Mutagenesis and cytotoxicity were studied in Escherichia coli by iproplatin and carboplatin, two analogs of cisplatin (CDDP) currently undergoing clinical trial. As with CDDP, mutagenesis by these agents was mediated by the umuDC gene product. In contrast to CDDP, however, mismatch repair did not substantially contribute to survival of cells after exposure to these agents since dam-3 E. coli were not more sensitive than wild type E. coli. UvrA- E. coli, however were more sensitive to these analogs demonstrating that as with CDDP, uvr endonuclease-mediated excision contributes to the repair of DNA damage induced by platinum compounds.     

Location of DNA methylation genes on the Escherichia coli K-12 genetic map

Summary The genes responsible for DNA adenine methylation (dam) and DNA cytosine methylation (dcm) have been mapped on the E. coli K-12 genetic map. The dam gene is situated at min 65 and the gene order cysG-(trpS, dam)-aro B inferred. The dcm gene is located at min 37.5 and the gene order is supD-dcm-flaA1. In F merodiploids, the dam and dcm alleles are recessive.