The Distribution of Substances in the Sporangiophores of Peronospora parasitica (Pers. ex Fr.) Fr.

The distribution of nuclei, RNA, mitochondria, lipid material,protein, and insoluble carbohydrates in the developing sporangiophoresof Peronospora parasitica was demonstrated by cytochemical staining.Nuclei, mitochondria, and protein showed a more or less uniformdistribution throughout the young sporangiophores, but werelocated almost entirely within the mature spores when sporedispersal commenced. Lipid material had a similar distribution,but was absent from the sporangiophore apex and sporangiophorebranch tips during the early stages of development. RNA wasabundant in the sporangiophore apices during early development,but occurred only within the spores, in small quantities, atmaturation. Although insoluble carbohydrates were sparse, theyhad a similar distribution to the nuclei, mitochondria, andprotein. Glycogen was not detected. The major soluble carbohydrates, present in the mature sporesin about equal proportions, were identified by thin-layer chromatographyas trehalose and an aldo-hexose, either glucose or mannose.These sugars were present in about equal quantities in the immaturesporangiophores and spores, while in the mature sporangiophoresfrom which the spores had been removed, trehalose was the majorsugar present. Sugar alcohols were not detected.     

Sudden expansion of a single brown bear maternal lineage across northern continental Eurasia after the last ice age: a general demographic model for mammals?

The brown bear has proved a useful model for studying Late Quaternary mammalian phylogeography. However, information is lacking from northern continental Eurasia, which constitutes a large part of the species' current distribution. We analysed mitochondrial DNA sequences (totalling 1943 bp) from 205 bears from northeast Europe and Russia in order to characterize the maternal phylogeography of bears in this region. We also estimated the formation times of the sampled brown bear lineages and those of its extinct relative, the cave bear.
Four closely related haplogroups belonging to a single mitochondrial subclade were identified in northern continental Eurasia. Several haplotypes were found throughout the whole study area, while one haplogroup was restricted to Kamchatka. The haplotype network, estimated divergence times and various statistical tests indicated that bears in northern continental Eurasia recently underwent a sudden expansion, preceded by a severe bottleneck. This brown bear population was therefore most likely founded by a small number of bears that were restricted to a single refuge area during the last glacial maximum. This pattern has been described previously for other mammal species and as such may represent one general model for the phylogeography of Eurasian mammals. Bayesian divergence time estimates are presented for different brown and cave bear clades. Moreover, our results demonstrate the extent of substitution rate variation occurring throughout the phylogenetic tree, highlighting the need for appropriate calibration when estimating divergence times.     

Effects of ozone on wild plants

Although there is a great deal of concern about the effects of human activities on biodiversity, until recently there has been very little interest in the effects of ozone on the species that constitute the major part of the flora, the diverse herbaceous and shrubby species of natural and semi-natural communities. However, many wild species have been shown to be at least as sensitive to ozone as crops that show significant yield losses, so there is a pressing need for an evaluation of the risk to wild species posed by ozone. This review attempts to assess progress and highlight problems. It begins with a comment on semantics, discusses the difficulties involved in measuring relative ozone resistance and then proceeds to consider the effects of ozone on growth and resource allocation. The evidence for evolution of resistance is appraised and then the potential effects of several interactions (cutting/grazing, competition, soil water deficit and nutrition) are considered. The review ends with some remarks on observation of oxidant-induced changes in ecosystems.