Isolation of the Kinetoplast DNA of Leishmania tarentolae in the Form of a Network*

The major kinetoplast DNA complement of Leishmania tarentolae promastigotes has been isolated as a single sheet of interconnected molecules on the basis of its relative stability to shear forces and its high sedimentation coefficient. Two successive differential centrifugations were sufficient to recover 50 ± 10% of the total kinetoplast DNA free of nuclear DNA contamination. We use the term “network” to describe this unusual type of DNA configuration. Leishmania networks have a molecular weight of ～10¹⁰ daltons and an S_20,W in neutral sucrose gradients of 1729 7plusmn; 189 [n = 19] and exhibit an extremely low specific viscosity due to the compactness of packing of the DNA. The networks were visualized in the electron microscope, and in the light microscope either by fluorescence in solution after staining with acridine orange or in dried smears after staining with Giemsa. Purified networks from stationary phase cells banded in the position characteristic of closed monomeric minicircles in ethidum bromide-CsCl equilibrium gradients, and were stable in alkaline sucrose. Treatment of the closed networks with RNase and pronase had no effect on the ethidium bromide-CsCl banding pattern. However, treatment of closed networks with DNase I or II, X-irradiation or γ-irradiation changed the banding pattern by introducing single strand and double strand breaks, yielding an upper band and in some cases a intermediate band.     

The orthopteroid insects described by Linnaeus, with notes on the Linnaean collection

A list is given of the recently recurated Orthoptera s.l. held by the Linnean Society of London. The status of specimens in the collection is evaluated, eight lectotype designations are made, and the orthopteroid species described by Linnaeus are listed alphabetically.     

In Vitro Response of Blastocystis hominis to Antiprotozoal Drugs

Ten antiprotozoal drugs were tested in vitro against four axenic strains of the intestinal parasite Blastocystis hominis. Inhibitory drugs in order of effectiveness were emetine, metronidazole, furazolidone, trimethoprim sulfamethoxazole, 5-chloro-8-hydroxy-7-iodo-quinoline (Entero-Vioform), and pentamidine. Moderately inhibitory were two quinolines other than iodochlorhydroxquin. These were chloroquine and 5, 7-diiodo-8-hydroxy-quinoline(Floraquin). Diloxanide furoate was not inhibitory. Paromomycin and other antibiotics were not inhibitory. Entero-Vioform and metronidazole have been effective in human and higher primate diarrhea caused by B. hominis.     

Chilling Sensitivity of Photosynthetic Oil-Seedlings

Seed germination and seedling emergence are particularly sensitiveto low temperatures in oil-seed genera in which lipids are themain seed storage material, e g cotton, corn, cucumber, andwatermelon Growth of photosynthetic seedlings of oil-seed generais also significantly affected by suboptimal temperatures. Aphotosynthetic seedling growth system used to demonstrate suboptimaltemperature stress effects in cotton was modified to monitorthe effects of temperatures from 10 to 35 ? upon the roots andaerial portions of cucumber, cantaloupe, and watermelon seedlings.Non-destructive measurements of fresh weights and the relativewater contents of the roots and shoots of seedlings grown at30 ? and at non-optimal temperatures, as well as chilled seedlingsreturned to 30 ? for one day, indicated significant intra-genencdifferences in temperature sensitivity and relative root andshoot water status of both the chilled seedlings and those recoveringfrom thermal stress The capacity to return to normal water statusand resume growth differed between and within species and wascorrelated with recommendations for chilling tolerance Key words: Temperature, water stress, photosynthetic seedling     

Angle Meristem Origin and Development in Selaginella martensii

The origin and early development of angle meristems (AMs) inSelaginella martensii were studied using a high-resolution mouldand cast technique for scanning electron microscopy, in conjunctionwith light microscopy. Both dorsal and ventral AMs originatein the apical region shortly after the most recent bifurcationof the shoot apex. AMs appear to arise from a single superficialinitial cell, which subsequently undergoes an oblique anticlinaldivision to establish the apical cell of the AM. The AM apicalcell has a relatively short active life and divides laterallyusually only six to twelve times; most cells of the AM originatefrom repeated divisions of apical cell derivatives. Dorsal andventral AMs show similar developmental sequences, although theydiffer slightly in time of appearance. Ventral AMs originatedfirst, dorsal AMs appearing shortly thereafter. At a given branchpoint, the ventral AM is typically larger than the correspondingdorsal AM. Both dorsal and ventral AMs grow out as rhizophores(aerial roots), although ventral AM development greatly precedesdorsal AM development. It is possible that the apparent earlierdecrease in apical cell activity in dorsal AMs compared to ventralAMs could account for the lag in dorsal AM development as arhizophore at a given branch point. Selaginella martensii Spring, Lycophyta, angle meristem, apical cell, morphogenesis, mould and cast technique, replica technique, scanning electron microscopy     

Further work on the genetics of race specific resistance in lettuce (Lactuca sativa) to downy mildew (Bremia lactucae)

Data are presented on the segregation of resistance to four races of Bremia lactucae in the F2 progenies of crosses involving 15 resistant and various susceptible lettuce cultivars. Most of these data and those recently published by other workers fit the systematic model for the genetics of race specific resistance to B. lactucae proposed by Crute & Johnson(1976). Seven different dominant resistance genes of major effect were found. There was also evidence of a pair of dominant genes with complementary effect, one of which may sometimes be effective on its own. Two of the genes may be linked and another may have two different alleles for resistance at the same locus. The resistance conferred by these genes is specified in relation to two British, two Dutch and four French races of the fungus. Resistance genotypes are proposed for 16 cultivars.     

The transition from planktotrophy to lecithotrophy in larvae of Lower Palaeozoic Rhynchonelliform brachiopods

Criteria are established for defining the presence of protegula formed on embryonic or larval mantle in representative genera of Lower Palaeozoic Obolellata, Strophomenata and Rhynchonellata. Width was used to define protegular type. Taxa with only an embryonic protegulum are inferred to have had lecithotrophic larvae while taxa with a larval protegulum or an embryonic protegulum surrounded by a larval protegulum are inferred to have had planktotrophic larvae. All or most of the taxa examined in the Obolellata, the Strophomenata and the orders Protorothida and Orthida in the Rhynchonellata had planktotrophic larvae. In the Pentamerida a minority of genera had only a larval, or an embryonic and a larval protegulum while a majority had protegular widths indicating lecithotrophy. In the orders Rhynchonellida, Atrypida, Athyrida and Spiriferida derived from the Pentamerida (with the exception of one species in the Atrypida) a number of the genera had protegular widths indicating lecithotrophy. It is suggested that the onset of lecithotrophy in the Pentamerida was associated with a developmental innovation in which the mantle lobe of the larva was reflected over the apical lobe during the process of metamorphosis. This evolutionary innovation probably occurred during the late Cambrian or early Ordovician and was subsequently inherited during the process of cladogenesis.     

Macroinvertebrate community response to natural and forest harvest gradients in western Oregon headwater streams

1. To examine the effects of forest harvest practices on headwater stream macroinvertebrates, we compiled a 167 site database with macroinvertebrate, fish, physical habitat and catchment land cover data from the three forested ecoregions in western Oregon. For our analysis, headwater streams were defined by catchment areas <10 km² and perennial water during summer low flows. Almost all sites in the database were selected using a randomised survey design, constituting a representative sample of headwater streams in these ecoregions. 2. Macroinvertebrate taxonomic and functional feeding group composition were very similar among the three ecoregions in the study area (Coast Range, Cascades and Klamath Mountains). On average, 55% of the individuals at each site were in the orders Ephemeroptera, Plecoptera or Trichoptera. Dipteran taxa (mostly chironomids) accounted for another 34%. At almost all sites, non‐insects made up <10% of the macroinvertebrate assemblage. Almost half (49%) of the assemblages were collectors; remaining individuals were about evenly divided among scrapers, shredders and predators. 3. There were 189 different macroinvertebrate taxa at the 167 sites with richness at individual sites ranging from 7 to 71 taxa. Ordination by non‐metric multidimensional scaling revealed a strong association between % Ephemeroptera, especially Baetis, and site scores along the first axis. This axis was also strongly related to % coarse substratum and fast water habitat. The second axis was strongly related to % intolerant individuals, site slope and altitude. No strong relationships were evident between any ordination axis and either logging activity, presence/absence of fish, catchment size or ecoregion. 4. Based on macroinvertebrate index of biotic integrity (IBI) scores, 62% of the sites had no impairment, 31% of the sites had slight impairment and only 6% of the sites had moderate or severe impairment. IBI scores were not strongly related to forest harvest history. All four severely impaired sites and five of the seven sites with moderate impairment were lower altitude, shallower slope stream reaches located in the Coast Range with evidence of agricultural activity in their catchment or riparian zone. % sand + fine substratum was the environmental variable most strongly related to macroinvertebrate IBI.     

New capabilities for Mycosphaerella graminicola research

Mycosphaerella graminicola is a major pathogen of wheat worldwide, causing Septoria leaf blotch disease. Targeted gene disruption in M. graminicola, by Agrobacterium tumefaciens‐mediated transformation, has become an established functional genomics tool for M. graminicola research in recent years. However, in order to advance research into this economically important pathogen, further functional genomics tools need to be developed. Here, we report three new capabilities for M. graminicola research: (i) two selectable markers have been shown to work robustly in M. graminicola, namely G418 and the fungicide carboxin; (ii) the generation of a strain of M. graminicola in which the KU70 (MUS‐51) homologue has been disrupted; in this strain, homologous recombination efficiencies increased to more than 95%, whilst maintaining wild‐type growth in vitro and full pathogenicity on wheat leaves; (iii) the ability to efficiently target and generate precise mutations of specific genes in the genomic context in M. graminicola. In addition, the insertion of the E198A mutation into the β‐tubulin gene (MgTUB1), conferring resistance to the fungicide benomyl, suggests that this mutant allele may provide an additional selectable marker. The collective use of these tools will permit further advancements in our knowledge of the biology and pathogenicity of this important plant pathogen.