Seed set in Phormium: interactive effects of pollinator behaviour,pollen carryover and pollen source

Summary Fruit and seed set was studied in New Zealand flax (Phormium tenax Phormiaceae) a large monocot that preferentially sets outcrossed seeds. Fruit set was low and in particular situations could result from insufficient pollinator visitation. Observations of pollinator (Meliphagidae) movements showed that birds preferentially visited male phase flowers and predominantly moved pollen within inflorescences of the same plant. More dominant resident birds moved more between plants that subordinate non-resident birds. Combination of results of fluorescent dye carryover with known bird movements allowed predictions of fruit set and seed size that closely approximated observed levels. Resident birds account for almost half the observed foraging bouts but are predicted to be responsible for the vast majority of the viable seeds.     

Efficacy of triclabendazole against fascioloidiasis (Fascioloides magna) in naturally infected white-tailed deer (Odocoileus virginianus)

The efficacy of triclabendazole was evaluated in the treatment of naturally acquired Fascioloides magna infections in white-tailed deer (Odocoileus virginianus). Twenty white-tailed deer were captured on the Welder Wildlife Refuge (Sinton, San Patricio County, Texas, USA) and maintained in a 64 x 64 m deer enclosure. Ten deer were given a 5% suspension of triclabendazole orally at a dosage of 10 mg/kg body weight and 10 deer were given a placebo. Three wk later the deer were euthanized and examined for parasites. At necropsy 19 deer were infected. All specimens of F. magna from the tissues of the triclabendazole treated deer were dead or severely affected by the drug as indicated by changes in their size, color, movement and texture relative to those from control deer. The drug was considered 100% effective against this parasite. Adverse reactions of the deer to the drug were not observed.     

Neuronal gene expression in aluminum myelopathy

1. Aluminum administration to susceptible animal species results in neurofilament accumulation in neuronal perikarya and proximal axons. Pathogenetic studies in vivo have shown that aluminum rapidly associates with neuronal chromatin. Whether the effect of aluminum on DNA components plays a role in the production of the neurofibrillary lesion remains unclear. 2. In this study we used Northern analysis and in situ hybridization to evaluate mRNA levels of specific neuronal and glial components in the rabbit spinal cord at various times following aluminum administration. 3. Our results show that (a) all neuronal mRNAs evaluated (neurofilament triplet components, neuronal-specific enolase, and amyloid precursor protein) are markedly decreased, with no decrease in glial fibrillary acidic protein; (b) the effect on neuronal gene expression occurs early and concurrently with the development of the neurofibrillary lesion and reverses rapidly after a single dose of aluminum; and (c) there is a direct correlation between the severity of the neurofibrillary lesion and the decrease in neuronal mRNA levels. 4. We interpret our results to mean that the accumulation of neurofilaments in this model is not due to a selective effect on neurofilament gene expression but may be due to an inhibition of genes coding for components involved in processing of neurofilament proteins.     

Role of light, carbon dioxide and nitrogen in regulation of buoyancy, growth and bloom formation of Anabaena flos-aquae

The availability of light, CO₂ and NH₄-N interacted to controlbuoyancy and growth of the gas vacuolate blue-green alga, Anabaenaflos-aquae. At high light intensities algal growth rates werehigh; however, the alga was non-buoyant regardless of the availabilityof CO₂ or NH₄-N. The mechanism for buoyancy loss involved increasedcell turgor pressures at higher light intensities which resultedin collapse of gas vacuoles. At lower light intensities algalgrowth rates and cell turgor pressures were reduced and buoyancywas controlled by the availability of CO₂ and inorganic nitrogen.Carbon dioxide limitation increased buoyancy, while reducedinorganic nitrogen availability reduced buoyancy. Mechanismsfor buoyancy regulation at low light intensities involved changesin cellular C/N ratios which appeared to affect the rate ofsynthesis and accumulation of protein-rich gas vacuoles. Algalspecific growth rates were combined with buoyancy data to forma single index (µ_bloom) to the rate of surface bloom formationof A.flos-aquae as a function of the availability of light,CO₂ and NH₄-N. The bloom formation index was enhanced with decreasedavailability of light and CO₂, and increased availability ofNH₄-N.     

Photosynthetic properties of leaves of a yellow green mutant of wheat compared to its wild type

We investigated several photosynthetic parameters of a virescent mutant of durum wheat and of its wild-type. Electron transport rate to ferricyanide was the same in the two genotypes when expressed on leaf area basis while O₂ evolution of the leaf tissue in saturating light and CO₂ was slightly higher in the yellow genotype. RuBPCase was also slightly higher. Quantum yield per absorbed light was similar in the two genotypes. P700 and Cyt f were less concentrated in the mutant while PS II was only marginally lower. The light response curve of CO₂ assimilation indicated higher level of photosynthesis of the mutant in high light, which corresponded to a lower non-photochemical quenching compared to the wild-type. It is concluded that the reaction centres, cyt f and chlorophyll are not limiting factors of electron transport in wheat seedlings and that electron transport capacity is in excess with respect to that needed for driving photosynthesis. Since the differences in photosynthesis reflect differences in RuBPCase activity, it is suggested that this enzyme limits photosynthesis in wheat seedlings also at high light intensities.Abbreviations cyt f cytochrome f - chl chlorophyll - PS II photosystem II - Pn_max maximum photosynthesis - RuBCase Ribulose, 1-5,bisphosphate carboxylase     

Characterization of GATA/GACA-related sequences on proximal chromosome 17 of the mouse

Chromosome behaviour during meiosis in male Syrian hamsters heterozygous for one of three translocations was analysed as part of a study of the transmission of these structural changes. Synapsis was studied using preparations of synaptonemal complexes, and chiasmate associations and the results of anaphase I segregation were studied in air-dried preparations of metaphases I and II respectively. The main findings were: (i) that, at least in the two trivalent-forming translocations, there is no simple relationship between either the frequency or the extent of synapsis and chiasma formation between the chromosomes involved in the translocation; (ii) that the presence of a univalent in a substantial proportion of metaphase I cells does not necessarily lead to irregular segregation as judged by analysis of metaphase IIs; and (iii) conversely, that in translocation heterozyotes in which metaphase I contains the chromosomes involved in the translocation as a quadrivalent or as two bivalents, with no univalents or trivalents, unexpected numerical segregation can be found. The observations of meiotic chromosomes behaviour reported here show that it is not always possible to predict the effects of structural change, or to determine the basis of these effects, from an analysis of any stage of meiosis taken in isolation, or from an analysis of an apparently similar change.     

Glandular trichome exudate is the critical factor in geranium resistance to foxglove aphid

Resistance to the foxglove-aphid (Acyrthosiphon solani Kaltenbach) has been demonstrated in some inbred geranium lines (Pelargonium Xhortorum Bailey). To establish more definitively the cause/effect relationship between tall glandular trichome exudate and resistance, an intact plant bioassay was performed comparing a resistant plant line, a resistant plant line from which the tall glandular trichome exudate had been removed using a basic buffer solution, a susceptible line and a susceptible line treated with the buffer wash. After 5 days of isolation on the respective surfaces, the number of surviving adult aphids as well as the number of nymphs produced and remaining alive were determined. Aphids on the buffer washed, resistant line exhibited mortality and fecundity which was not significantly different from that produced by the susceptible line. In contrast, the untreated resistance line was clearly resistant with lower adult survival and fewer living nymphs. The tall glandular trichome exudate must therefore be a critical factor in geranium resistance to the foxglove aphid.

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Zusammenfassung Widerstandsfähigkeit dem Fingerhut-Blattlaus (Acyrthosiphon solani Kaltenbach) gegenüber wurde in einigen durch Inzucht erzeugten Pelargonie-Linien (Pelargonium Xhortorum Bailey) gezeigt. Um das Verhältnis von Ursache und Wirkung zwischen dem hochgewachsenen glandulären Trichom-Exudat und Widerstandsfähigkeit genauer zu bestimmen, wurde eine Bio-Untersuchung an intakten Pflanzen unternommen. Dabei wurden eine widerstandsfähige Pflanzenlinie, eine widerstandsfähige Pflanzenlinie, von der das hochgewachsene glanduläre Trichom-Exudat durch eine basische Pufferlösung entfernt worden war, eine anfällige Linie und eine mit Pufferlösung behandelte Linie verglichen. Zwei erwachsene weibliche Blattläuse wurden fünf Tage durch ein engmaschiges Netz auf den zu untersuchenden dritten und vierten Knotenblättern eingesperrt. Bei jeder Pflanze wurde die Untersuchung an einem nichtbehandelten Blatt und an einem Blat, von dem das Exudat durch Waschen mit der Pufferlösung entfernt worden war, durchgeführt. Für jede Linie wurden fünf Pflanzen gebraucht, und der ganze Versuch wurde sechsmal wiederholt. Nach einer fünftägigen Isolierung auf den jeweiligen Oberflächen wurden die Blätter von der Pflanze entfernt, und sowohl die Zahl der überlebenden erwachsenen Blattläuse wie auch die der produzierten und noch am Leben gebliebenen Nymphen festgestellt. Mit einer niedrigeren Überlebensrate der Erwachsenen und weniger noch lebenden Nymphen war die nichtbehandelte widerstandsfähige Linie deutlich widerstandsfähig. Im Gegensatz dazu zeigten die Blattläuse auf der mit Puffer gewaschenen widerstandsfähigen Linie eine Sterblichkeit und Fruchtbarkeit, die nicht erheblich höher waren, als die auf der anfälligen Linie, was beweist, daß das Waschen mit der Pufferlösung den Widerstandsfaktor entfernt hatte. Das hochgewachsene glanduläre Trichom-Exudat muß deshalb ein kritischer Faktor in der Widerstandsfähigkeit gegen Pelargonie-Schädlinge sein.

     

Purification and characterization of a methionine-specific aminopeptidase from Salmonella typhimurium

An aminopeptidase specific for methionine (peptidase M) has been purified from wild-type and mutant Salmonella typhimurium strains. Recombinant peptidase M was also purified from Escherichia coli. These preparations were characterized with respect to their physicochemical properties using analytical ultracentrifugation, SDS/PAGE, isoelectric focusing, titration curve analysis, amino acid analysis, N-and C-terminal sequencing and various spectroscopic methods. Peptidase M activity is stimulated by Co2+, in agreement with previous studies using crude extracts of Salmonella. The purified preparations did not contain significant amounts of any metal. Enzymically important metal is loosely associated and lost during enzyme purification. Peptidase M was shown to contain seven free sulphydryl residues none of which are involved in either intra-or inter-molecular disulphide bonds. Most appear solvent-accessible as evidenced by their reactivity under native conditions. Limited modification of the sulphydryl residues with either iodoacetamide or 5,5'-dithiobis(2-nitrobenzoic acid) led to inactivation. Several cysteines were shown to be labelled to various degrees by peptide mapping of inactivated S-[14C]carboxymethylated protein. Whether cysteine modification affects enzymic activity directly (blocking an active site) or indirectly (by causing conformational change) remains to be established.     

Effect of Growth Rate and Starvation-Survival on the Viability and Stability of a Psychrophilic Marine Bacterium

Cell populations of the marine bacterium ANT-300, from either batch or continuous culture with dilution rates ranging from D = 0.015 h⁻¹ to D = 0.200 h⁻¹, were monitored for viability, direct counts, and optical density for 98 days under starvation conditions. Three stages of starvation survival were observed for each of the cell populations. Although direct counts remained at 2 × 10⁷ to 3 × 10⁷ cells ml⁻¹ throughout the starvation period, large fluctuations occurred in cell viability during stage 1 (0 to 14 days) of starvation survival. Stage 2 (14 to 70 days) involved an overall decrease in viability for each of the cell populations; the rate of viability loss was dependent upon the growth rate. Cell viability stabilized at approximately 0.3% of the direct count in stage 3 (70 to 98 days). Long-term starvation corresponded to the prolongation of stage 3 starvation survival. Cell volumes for each of the cell populations decreased with the length of the starvation period. However, the cell volume of starved cells was also dependent more on growth rate than on the length of the time starved. We hypothesize that the cell population with the slowest growth rate is most closely representative of cells found in the oligotrophic marine environment.