Low Levels of Genetic Diversity within Populations of Hosta clausa (Liliaceae)

Abstract Genetic diversity of Korean populations in Hosta clausa was investigated using starch gel electrophoresis. Hosta clausa is widespread, grows only along streamsides, and has both sexual and asexual reproduction. Populations of the species are small and isolated. Thirty-two percent of the loci examined were polymorphic, and mean genetic diversity within populations (He_p=0.082) was lower than mean estimates for species with very similar life history characteristics (0.131), particularly for its congener H. yingeri (0.250). The mean number of multilocus genotypes per population was 8.7, and genotypic diversity index (D_G) was 0.84. Significant differences in allele frequencies among populations were found in all seven polymorphic loci (P < 0.001). About one-fifth of the total allozyme variation was among populations (G_ST=0.192). Indirect estimate of the number of migrants per generation (Nm=0.48, calculated from mean G_ST) and nine private alleles found indicate that gene movement among populations was low. The low levels of genetic diversity within populations and the relatively high levels of genetic diversity among populations suggest that strong moist habitat preferences, clonal reproduction, low level of gene flow among populations, genetic drift, and historical events may have played roles in the genetic structuring of the species.     

Interaction of poly(L-lysine) and copolymers of lysine with immobilized DNA.

Sonicated DNA has been covalently attached to Sepharose 4B by a carbodiimide method [Rickwood, P. (1972) Biochim. Biophys. Acta269, 47–50] which minimizes modification of the DNA and matrix. Columns of this material have been used to study the interaction between cationic polypeptides and DNA. When poly(l-lysine) is bound to such columns at low ionic strength and then eluted with a linear salt gradient the polypeptide elutes over a broad range of salt concentration, presumably reflecting different strengths of interaction with various sites on the DNA. The broadness of the elution profile cannot be attributed to heterogeneity in the poly(l-lysine) sample but rather to the $\text{AT}\text{GC}$ content of various DNA sites. Studies with other polypeptides, poly(l-Lys⁷⁹, l-Leu²¹) and poly-(l-Lys-l-Ala-Gly), as well as studies at different temperatures, have helped to clarify the possible roles of conformational mobility, polypeptide hydrophobicity, and the presence of contiguous lysines in determining the strength of interaction of polypeptides and proteins with DNA sites.     

Purification and properties of malate dehydrogenase from the extreme thermophileBacillus caldolyticus

The enzyme malate dehydrogenase (EC 1.1.1.37) from an extreme thermophileB. Caldolyticus was purified to about 91% homogeneity. The molar mass of the enzyme was determined as 73 000 daltons and it is composed of two subunits, each with a molar mass of 37 000. Initial velocity studies with oxaloacetic acid and NADH as substrates at pH 8.1, over a range of temperatures, indicate that the enzyme operates via a sequential type mechanism. Van't Hoff plots of the kinetic parameters displayed sharp changes in slope at characteristic temperatures, whereas the Arrhenius plot exhibited no such breaks over the temperature interval investigated. The enzyme was found to be stable at 41°C and lower temperatures. At 51°C and 59°C an almost immediate 20% reduction in activity was obtained, but no further inactivation occurred during the 60 min of incubation. At 59°C the enzyme lost 50% of its initial activity in about 38 s. High concentration of NADH was observed to greatly stabilize the enzyme at that temperature.It is suggested that the slope changes in the Van't Hoff plots and the stability profies at 51°C and 59°C are representative of a temperature induced conformational change in the enzyme.Proceedings of the Fourth College Park Colloquium on Chemical Evolution:Limits of Life, University of Maryland, College Park, 18–20 October 1978.     

Partial purification and characterization of nitrous oxide reductase fromParacoccus denitrificans

We report the first partial purification of nitrous oxide reductase, a unique and labile enzyme of denitrifying bacteria. The procedure, which required anaerobic conditions throughout, resulted in a 60-fold purification relative to crude lysate in the case ofParococcus denitrificans. The molecular weight was estimated by gel exclusion chromatography to be about 85,000. The partially purified enzyme is inactivated rapidly by O₂, dithionite, and mercaptoethanol and is reversibly inhibited by moderate concentrations of common salts. Up to 80% of the original activity can be reconstituted following O₂ inactivation by incubating the enzyme with reduced benzyl viologen for 2 to 3 h. TheV _max pH profile shows a broad maximum at pH 8. The enzyme is irreversibly retained by common anion exchangers in the range pH 7 to 8 but can be eluted in acceptable yield as one of the last components from an imidazole-based anion exchange material by means of a pH gradient. This behavior implies that nitrous oxide reductase is very acidic. Among the several peptides observed by sodium dodecyl sulfate slab electrophoresis, only two, with apparent molecular weights of 58,000 and 25,000, correlated closely with the activity of fractions eluted from the imidazole column. These two peptides together comprised about 30% of the total protein in the fractions with highest specific activity.     

Cassava leaf harvesting as vegetables; a cause of vulnerability of cassava plant to cassava mosaic disease and eventual yield reduction: Ernte von cassavablättern als gemüse; eine ursache für die anfälligkeit der cassavapflanze für die cassava-mosaikkrankheit und für spätere ertragseinbußen

The consequence of harvesting young leaves of cassava as vegetable on the vulnerability of the crop to cassava mosaic disease (CMD) and on storage root yield was investigated using 30 cassava genotypes planted in IITA fields located in the humid forest (Port Harcourt?:?Onne), forest-savannah transition (Ibadan), southern guinea savannah (Mokwa) and northern guinea savannah (Zaria) agroecologies in Nigeria. Tender apical leaves and shoots of the cassava genotypes were removed from forty plants per cassava genotype with the same number of plants considered as control. Whitefly infestation, disease incidence (DI) and symptom severity (ISS) of the disease were assessed at monthly interval for six months and also at the ninth month after planting (MAP). Yield reduction due to this treatment was calculated as percentage harvest index (HI). Whitefly population fluctuated throughout the period of observation at all locations with higher population obtained generally for treated plants compared to control plants. Sprouting leaves of some treated genotypes were observed with severe mosaic symptoms, while corresponding control showed no mosaic symptoms. Contrarily, no remarkable difference was observed in Zaria between the mean ISS of treated and control cassava genotypes. There was a highly significant difference (P?<?0.01) in DI and ISS among cassava genotypes across all locations. Also, there was a highly significant interaction (P?<?0.01) in symptom severity between location (loc) and genotype, genotype and treatment (trt), loc and trt. Interaction between loc, genotypes and trt with regard to DI was highly significant at 2, 3 and 4 MAP, while with ISS, the interaction was highly significant all through the counting period. There was a positive relationship between DI and ISS on plants of genotypes 96/1039 and ISU. The percentage HI (27.4) of treated plants of genotype 95/0166 in Ibadan was remarkably lower than the value obtained for corresponding control (41.9) plants. Also, sharp distinction in% HI of treated (39.5) and control (43.8) ISU was observed in Onne with their respective ISS values as 3.7 and 3.2. Therefore, harvesting tender apical leaves and shoots of cassava as vegetables should be discouraged as it increases the severity of CMD infection in the regenerating shoots of cassava with attendant storage root yield reduction.     

Isolation and characterization of a mixotrophic sulfur-oxidizing Thermus scotoductus

Thermophilic, faculatatively mixotrophic sulfur-oxidizing bacteria were isolated from a sulfide-rich, neutral hot spring in Iceland. The strain, IT-7254, used thiosulfate and elemental sulfur as electron donors, oxygen and nitrate as electron acceptors, and acetate and other organic compounds as carbon sources. After a few days of growth in the presence of thiosulfate, this strain formed sulfur globules. Comparison of intracellular enzymes and heme proteins of heterotrophically and mixotrophically grown cells showed some differences. The new isolate belonged to Thermus scotoductus because the small subunit (SSU) rRNA gene sequence analysis showed 98.6% sequence similarity and 84% DNA:DNA reassociation to Thermus scotoductus NMX2 A. 1. It is also close to Thermus antranikianii HN3-7, with 98.3% and 79% SSU rRNA sequence similarity and DNA:DNA reassociation, respectively. It was also found that both Thermus NMX2 A.1 and T. antranikianii HN3-7 were able to oxidize thiosulfate but that the T. scotoductus type strain SE-1 was not. This is the first report of Thermus strains that are capable of mixotrophic growth with sulfur oxidation.     

Inhibition of cGMP-dependent protein kinase II by its own splice isoform

cGMP- and cAMP-dependent protein kinases (cGK I, cGK II, and cAK) are important mediators of many signaling pathways that increase cyclic nucleotide concentrations and ultimately phosphorylation of substrates vital to cellular functions. Here we demonstrate a novel mRNA splice isoform of cGK II arising from alternative 5' splicing within exon 11. The novel splice variant encodes a protein (cGK II Delta(441-469)) lacking 29 amino acids of the cGK II Mg-ATP-binding/catalytic domain, including the conserved glycine-rich loop consensus motif Gly-x-Gly-x-x-Gly-x-Val which interacts with ATP in the protein kinase family of enzymes. cGK II Delta(441-469) has no intrinsic enzymatic activity itself, however, it antagonizes cGK II and cGK I, but not cAK. Thus, the activation and cellular functions of cGK II may be determined not only by intracellular cGMP levels but also by alternative splicing which may regulate the balance of expression of cGK II versus its own inhibitor, cGK II Delta(441-469).     

Sulfolobicins, specific proteinaceous toxins produced by strains of the extremely thermophilic archaeal genus Sulfolobus

Several novel strains of "Sulfolobus islandicus" produced proteinaceous toxins, termed sulfolobicins, which killed cells of other strains of the same species, as well as of Sulfolobus solfataricus P1 and Sulfolobus shibatae B12, but not of the producer strains and of Sulfolobus acidocaldarius DSM639. The sulfolobicin purified from the strain HEN2/2 had a molecular mass of about 20 kDa. It was found to be associated with the producer cells as well as with cell-derived S-layer-coated spherical membrane vesicles 90 to 180 nm in diameter and was not released from the cells in soluble form.     

Seasonal mortality trends in tree‐feeding insects: a field experiment

Abstract 1. The majority of general life‐history models treat the environment as being invariable through time, even though temporal variation in selective agents could dramatically change the outcomes, e.g. in terms of optimal size and time at maturity. For herbivorous insects, seasonal differences in food quality are reasonably well described, but seasonal dynamics of top‐down selective forces are poorly documented. 2. The present study attempted to quantify seasonal changes in predation risk of folivorous insect larvae in temperate forest habitats. In a series of field experiments, artificial larvae were exposed to predators, and the resulting bird‐inflicted damage was recorded. The trials were repeated regularly throughout the course of two summers. 3. A distinct peak of larval mortality was recorded in mid‐June (the nestling period for most insectivorous passerine birds), after which predation risk declined to a plateau of 20–30% below the peak value. 4. The recorded pattern is interpreted as a consequence of seasonal changes in the number and behaviour of insectivorous birds, and the abundance of alternative food resources for these predators. 5. A quantitative analysis based on field data indicated that considering temporal variation in mortality in life‐history models is crucial for obtaining realistic predictions concerning central life‐history traits, such as final body size in different generations.