Gel electrophoresis studies of proteins from leaves of photoperiodically induced and vegetative cocklebur plants

Comparisons of proteins synthesized in photoperiodically-sensitiveleaves of induced and vegetative cocklebur plants were made.Fifteen or more protein bands could be separated by polyacrylamidegel electrophoresis when polyvinylpyrrolidone was used in theextracting buffer to remove phenolics. As contrasted to resultsof others with Pharbilis nil, no differences in stained bandingpatterns could be detected in vegetative and induced plants.Radioactive leucine, lysine and phenylalanine were incorporatedinto similar leaf proteins during the last half of an inductivedark period. These experiments and dual-labeling studies with³H- and ¹⁴C-phenylalanine indicated no consistent differencesin the types of extracted proteins synthesized by leaves ofvegetative and induced plants. ¹Present address: Plant Science Dept., Utah State University,Logan 84321, U.S.A. (Received October 26, 1970; )     

Perissothallus, a new genus for Late Pennsylvanian–Early Permian noncalcareous algae conventionally assigned to Schizopteris (aphleboid foliage)

The morphogenus Schizopteris was established in the early 19th century for late Palaeozoic aphleboid foliage of uncertain affinities, and numerous specimens have subsequently been assigned to this taxon. Some of these fossils do not represent foliage, but rather noncalcareous algae. Although this inconsistency has been noted, an attempt to exclude the algae from Schizopteris has not yet been undertaken. Here we propose the new genus Perissothallus to accommodate those fossils conventionally assigned to Schizopteris that represent algae. The name P. versiformis is introduced for the type species from the Upper Pennsylvanian of Kansas (USA). Specimens from the Lower Permian of Germany are interpreted as a second species of Perissothallus , and the name P. densus is proposed. Perissothallus consists of erect cylindrical branches that radiate from a small holdfast and dichotomize repeatedly. Vegetative reproduction occurs in the form of daughter thalli produced on prostrate branches. Similarities in basic structure exist between Perissothallus and members of the extant algal genera Codium (Chlorophyta), Dictyota (Phaeophyta), and Scinaia (Rhodophyta).  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 153 , 477–488.     

Hydroperiod,predators and the distribution of physid snails across the freshwater habitat gradient

1. Studies of species distributions across environmental gradients further our understanding of mechanisms regulating species diversity at the landscape scale. For some freshwater taxa the habitat gradient from small, shallow and temporary ponds to large, deep and permanent lakes has been shown to be an important environmental axis. Freshwater snails are key players in freshwater ecosystems, but there are no comprehensive studies of their distributions across the entire freshwater habitat gradient. Here we test the hypothesis that snail species in the family Physidae are distributed in a non‐random manner across the habitat gradient. We sampled the snails, their predators and the abiotic environment of 61 ponds and lakes, spanning a wide range in depth and hydroperiod. 2. Temporary habitats had the lowest biomass of predators. Shallow permanent ponds had the highest biomass of invertebrate predators but an intermediate fish biomass. Deep ponds and lakes had the highest fish biomass and intermediate invertebrate biomass. Five species of physids occurred in the regional species pool and 60 of the 61 ponds and lakes surveyed contained physid snails. Each pond and lake contained an average of just 1.2 physid species, illustrating limited membership in local communities and substantial among‐site heterogeneity in species composition. 3. Physids showed strong sorting along the habitat gradient, with Physa vernalis found in the shortest hydroperiod ponds and Aplexa elongata, P. gyrina, P. acuta and P. ancillaria found in habitats of successively greater permanence. When organised into a site‐by‐species incidence matrix with sites ordered according to their hydroperiods, we found the pattern of incidence to be highly coherent, showing that much of the heterogeneity in species composition from one pond to another is explained by hydroperiod. We also found that the number of species replacements along this gradient was higher than random, showing that replacement is more important than nesting in describing species composition in ponds of different hydroperiod. 4. Discriminant analysis showed that pond depth, invertebrate biomass and fish biomass were the best predictors of species composition. Analysis of these niche dimensions showed that P. vernalis and A. elongata were most successful in shallow, temporary ponds with few predators. P. gyrina and P. acuta were typically found in ponds of intermediate depth and high predator abundance. P. ancillaria was found in the deepest lakes, which had abundant fish predators but few invertebrate predators. Of the five species considered, P. ancillaria, P. vernalis and A. elongata were relatively specialised with regard to key habitat characteristics, P. gyrina was moderately generalised and P. acuta was remarkably generalised, since it alone occurred across the entire freshwater habitat gradient. The exceptional habitat breadth of P. acuta stands in contrast to distributional studies of other freshwater taxa and deserves further attention.     

Immediate Struggles: People, Power, and Place in Rural Spain

Immediate Struggles: People, Power, and Place in Rural Spain . Susana Narotzky and Gavin Smith. Berkeley: University of California Press, 2006. 250 pp.     

Accumulation of DNA damage in Antarctic mosses: correlations with ultraviolet-B radiation, temperature and turf water content vary among species

The susceptibility of three East Antarctic moss species to UV-B radiation was examined by measuring accumulation of cyclobutane pyrimidine dimers under natural sunlight during the austral summer season of 2002/03. The 2002/03 season was characterized by unusually low springtime ozone depletion and as such our results likely underestimate the DNA damage possible in a more typical UV-B radiation season. Despite this all three species accumulated significant DNA photoproducts. We also found a positive association between photoproduct accumulation and incident UV-B radiation in the two cosmopolitan species, Bryum pseudotriquetrum and Ceratodon purpureus , with more DNA damage in samples collected early in the season compared with later in the summer. For B. pseudotriquetrum , negative associations were also observed between photoproduct accumulation and both turf water content and the 10-day mean air temperature. Photoproduct accumulation in the endemic species Schistidium antarctici was similarly high across the season and no significant association with environmental variables was found. Our results are consistent with the two cosmopolitan species having somewhat higher UV-B-screening capabilities and possibly more efficient mechanisms for repairing DNA damage than the endemic S. antarctici .     

Maintenance of genetic variation in plants and pathogens involves complex networks of gene-for-gene interactions

The RPP13 [recognition of Hyaloperonospora arabidopsidis (previously known as Peronospora parasitica )] resistance ( R ) gene in Arabidopsis thaliana exhibits the highest reported level of sequence diversity among known R genes. Consistent with a co-evolutionary model, the matching effector protein ATR13 ( A. thaliana -recognized) from H. arabidopsidis reveals extreme levels of allelic diversity. We isolated 23 new RPP13 sequences from a UK metapopulation, giving a total of 47 when combined with previous studies. We used these in functional studies of the A. thaliana accessions for their resistance response to 16 isolates of H. arabidopsidis . We characterized the molecular basis of recognition by the expression of the corresponding ATR13 genes from these 16 isolates in these host accessions. This allowed the determination of which alleles of RPP13 were responsible for pathogen recognition and whether recognition was dependent on the RPP13/ATR13 combination. Linking our functional studies with phylogenetic analysis, we determined that: (i) the recognition of ATR13 is mediated by alleles in just a single RPP13 clade; (ii) RPP13 alleles in other clades have evolved the ability to detect other pathogen ATR protein(s); and (iii) at least one gene, unlinked to RPP13 in A. thaliana, detects a different subgroup of ATR13 alleles.     

Stem canker (Rhizoctonia solani) on five early and seven maincrop potato cultivars. II Effects on growth and yield

In 1983 and 1984, potato seed tubers of five early and seven maincrop cultivars were inoculated with cultures of Rhizoctonia solani during planting in field experiments to simulate severe seed infection. The size of foliage was assessed during June-August and tuber yields recorded during growth and at harvest in October. Stem canker delayed shoot emergence, decreased the number and length of stems and caused increased variation in stem length; these effects were greatest with Maris Peer and Arran Comet (early cultivars) and King Edward and Pentland Squire (maincrop cultivars). Total weight of foliage was decreased, especially with earlies, dry matter of stems increased and the proportion of foliage on lateral stems increased. With the early cultivars, tuber yield from sprouted Maris Peer seed 11 wk after planting in 1983 was decreased by 24%, and 13 wk after planting in 1984 yields were decreased by 42% (Maris Peer), 40% (Ulster Sceptre), 34% (Estima), 30% (Arran Comet) and 17% (Ulster Prince) with sprouted seed and by 20, 29, 53, 39 and 28% respectively with non-sprouted seed. Decrease in total yield at harvest in October averaged 13% with sprouted seed and 10% with non-sprouted seed. In all cultivars the weight of small tubers was decreased and with Estima the weight of large tubers was increased. Tuber bulking was also delayed with all maincrop cultivars and at harvest yields from sprouted King Edward seed were decreased by 13% in 1983 and by 16% (sprouted seed) and 23% (non-sprouted seed) in 1984; yields of Pentland Squire were decreased by 5, 16 and 21% respectively. Yield losses with other cultivars ranged from 5–13% with sprouted seed and 0–16% with non-sprouted seed. The yields of small tubers were decreased with all cultivars and yields of large tubers were increased with Pentland Squire, Pentland Crown and Cara.     

Similarities and Differences Among Prolactins and Growth Hormones and Their Receptors

SYNOPSIS. Data from the literature and from our own studieson the receptors for prolactin (PRL) and growth hormone (GH)are reviewed and analyzed. Receptors for PRL have been studiedin a wider range of species and in a greater diversity of targetorgans than have the binding sites for GH. Although GHs arestructurally more highly conserved among the vertebrates thanare PRLs, the available data indicate that there is greaterdiversity among GH receptors than there is among PRL receptors.In general, GH receptors show greater species specificity butless hormone specificity than do PRL receptors. The reason forthe greater diversity among GH receptors as compared to PRLreceptors is unknown; it bears no relationship to phylogeny. Data on the binding of purified preparations of mammalian PRL,GH and placental lactogen (PL) to renal and hepatic receptorsfor PRL and GH, respectively, of several vertebrate speciesare reviewed. The species and hormone specificity of the bindingof the hormones to the two typesof receptors showed no consistentpattern. To explain this disarray, we propose that the receptorbinding domains of PRL and GH were present in their common ancestralgene and that they havebeen retained to variable degrees byall of the descendant members of the PRL-GH family. We furtherpropose that hormone and species specificity of binding is determinedby hindering features on the hormones and on the receptors,rather than by merely the presence or absence of the appropriatebinding determinants.