Reinvasion of a Riparian Forest Community by an Animal-dispersed Tree Weed Following Control Measures

Patterns of seed dispersal and the effects of mulching upon Celtis sinensis Pers. seedling establishment were investigated following the removal of this tree weed from a riparian forest community. At the commencement of the study there was virtually no representation of C. sinensis in the soil seed bank. However, subsequent rates of seed immigration were high since mature individuals of C. sinensis remained on the boundary of the site. Fruit bats (Pteropus spp.) were the principal dispersal vectors. Seed rain density of C. sinensis was best fitted by an inverse power distribution, with seed densities in excess of 20 m⁻² detected at 70 m from the seed source. Extrapolation from this relationship suggested that a site would have to be more than 350 m from a seed source to reduce the C. sinensis seed rain to less than 1 m⁻². More than 98% of the seed rain occurred below the canopies of the native tree species that remained following the removal of C. sinensis. For these trees, subarboreal C. sinensis seed distributions were not homogeneous, with peak seed densities occurring at different distances from tree trunks in each of the two years that seed distributions were assessed. Mulching with compacted sugar cane trash, corresponding to litter loadings of 6–12 kg m⁻², was imposed early in the study, some weeks before the C. sinensis seed rain commenced. These treatments had no measurable effect upon C. sinensis germination, but substantially reduced seedling survival and had variable effects upon the early growth of seedlings. The potential roles of seed limitation vs establishment limitation are discussed in relation to the management of animal-dispersed invasive species. It is argued that an understanding of the likely levels and patterns of invasion is essential for the formulation of management strategies that can effectively reduce the invasion and impacts of these plants. This revised version was published online in July 2006 with corrections to the Cover Date.     

Novel method for the proteomic investigation of a dairy-associated Bacillus cereus biofilm

The biofilm proteome of a dairy-associated Bacillus cereus strain (B. cereus 5) was investigated. Biofilm biomass of sufficient concentration for 2D-PAGE was obtained by growing the culture in the presence of glass wool. B. cereus 5 readily attached to the glass wool and biofilms formed within 18 h. The biofilm proteome of whole-cell proteins revealed that 10 proteins were synthesized as a result of surface attachment of which four were unique to the biofilm profile. Seven proteins appeared to be absent in the biofilm profile. The altered proteomes indicated that changes took place in the regulation of protein expression when B. cereus 5 cells attached to surfaces.     

Adenylate kinase as a virulence factor of Pseudomonas aeruginosa

Adenylate kinase (AK; ATP:AMP phosphotransferase, EC 2.7.4.3) is a ubiquitous enzyme that contributes to the homeostasis of adenine nucleotides in eukaryotic and prokaryotic cells. AK catalyzes the reversible reaction Mg. ATP + AMP <--> Mg. ADP + ADP. In this study we show that AK secreted by the pathogenic strains of Pseudomonas aeruginosa appears to play an important role in macrophage cell death. We purified and characterized AK from the growth medium of a cystic fibrosis isolate strain of P. aeruginosa 8821 and hyperproduced it as a fusion protein with glutathione S-transferase. We demonstrated enhanced macrophage cell death in the presence of both the secreted and recombinant purified AK and its substrates AMP plus ATP or ADP. These data suggested that AK converts its substrates to a mixture of AMP, ADP, and ATP, which are potentially more cytotoxic than ATP alone. In addition, we observed increased macrophage killing in the presence of AK and ATP alone. Since the presence of ATPase activity on the macrophages was confirmed in the present work, external macrophage-effluxed ATP is converted to ADP, which in turn can be transformed by AK into a cytotoxic mixture of three adenine nucleotides. Evidence is presented in this study that secreted AK was detected in macrophages during infection with P. aeruginosa. Thus, the possible role of secreted AK as a virulence factor is in producing and keeping an intact pool of toxic mixtures of AMP, ADP, and ATP, which allows P. aeruginosa to exert its full virulence.     

Transformation of plant protoplasts with DNA: cotransformation of non-selected calf thymus carrier DNA and meiotic segregation of transforming DNA sequences

Summary With the DNA transformation procedure developed in our laboratory (13) several transformed tobacco SR1 tissues were obtained which, apart from selected and non-selected pTi sequences (T⁺), also had acquired non-selected calf thymus carrier DNA sequences (C⁺), being integrated in their nuclear genomes. From one such tissue (cNT4), with a shooty crown gall phenotype and expressing mannopine synthesis activity (Mas⁺), shoots were grafted and mature, flowering plants (gNT4) were obtained. After cross pollination with wild type SR1 tobacco pollen 49% of the seedlings obtained, had the maternal NT4-like crown gall phenotype and 51% showed wild type (SR1) features. The mannopine locus segregated independently from the locus determining the crown gall phenotype. When screened for integrated (transforming) foreign DNA sequences 97% of the NT4-like seedlings turned out to be C⁺T⁺. Most of the SR1-like seedlings, having a wild type tobacco morphology, proved to be transformed as well: roughly a 1:1:1:1 ratio as found for C⁺T⁺:C^-T⁺: C⁺T:C T SR1-like seedlings. Based on the segregation of transforming sequences during meiosis a model is presented showing the integration of these sequences in three different host chromosomes.     

Alleviation of deleterious effects of protein mutation through inactivation of molecular chaperones

Molecular chaperones recognize and bind destabilized proteins. This can be especially important for proteins whose stability is reduced by mutations. We focused our study on a major chaperone system, RAC-Ssb, which assists folding of newly synthesized polypeptides in the yeast cytosol. A sensitive phenotypic assay, the red color of Ade2 mutants, was used to screen for variants with metabolic activity dependent on RAC-Ssb. None of the Ade2 mutants were found to exhibit lower metabolic activity after inactivation of RAC-Ssb. In order to explicitly test the relationship between protein instability and activity of chaperones, a series of temperature sensitive Ade2 mutants were tested in the presence or absence of RAC-Ssb. The growth of Ade2(ts) mutants at elevated temperatures was enhanced if chaperones were missing. Similar pattern was found for thermally sensitive mutants of several other genes. Because RAC-Ssb normally supports the folding of proteins, it appears paradoxical that catabolic activity of mutants is reduced when these chaperones are present. We suggest that under non-stressful conditions, molecular chaperones are tuned to support folding of native proteins, but not that of mutated ones.     

Purification and molecular cloning of a new galactose-specific lectin from <Emphasis Type="Italic">Bauhinia variegata</Emphasis> seeds

A new galactose-specific lectin was purified from seeds of a Caesalpinoideae plant, Bauhinia variegata, by affinity chromatography on lactose-agarose. Protein extracts haemagglutinated rabbit and human erythrocytes (native and treated with proteolytic enzymes), showing preference for rabbit blood treated with papain and trypsin. Among various carbohydrates tested, the lectin was best inhibited by D-galactose and its derivatives, especially lactose. SDS-PAGE showed that the lectin, named BVL, has a pattern similar to other lectins isolated from the same genus, Bauhinia purpurea agglutinin (BPA). The molecular mass of BVL subunit is 32 871 Da, determined by MALDI-TOF spectrometry. DNA extracted from B. variegata young leaves and primers designed according to the B. purpurea lectin were used to generate specific fragments which were cloned and sequenced, revealing two distinct isoforms. The bvl gene sequence comprised an open reading frame of 876 base pairs which encodes a protein of 291 amino acids. The protein carried a putative signal peptide. The mature protein was predicted to have 263 amino acid residues and 28 963 Da in size.     

Novel pre-treatment processes to promote linen-containing fabrics properties

This study was undertaken to investigate the effect of plasma pre-treatment, followed by enzymatic treatment in the absence and presence of bleaching agent on the properties of linen and linen-containing fabrics. Different plasma gases (air, oxygen and nitrogen), enzymes (acid-cellulases, neutral-cellulase and alkaline-pectinase) as well as bleaching agents (peracetic acid and H₂O₂) were used. The changes in physico-mechanical properties, surface morphology and dyeing properties of the treated substrates have been investigated. The obtained results indicated that plasma pre-treatment followed by subsequent acid-cellulases/peracetic acid or alkaline-pectinase/H₂O₂ treatment result in: a dramatic improvement in hydrophilicity and wettability as well as in the degree of whiteness of the treated substrates, an improvement in reduction of surface roughness and extent of post-reactive dyeing, along with a weight loss and a drop in the tensile strength. The extent of surface modification as well as the changes in the above-mentioned properties are governed by the characteristics of the substrate, the plasma gas, the nature and dose of the used enzyme, as well as the type of bleaching agent and additive. The optimal treatment sequence for attaining better performance properties was O₂-plasma followed by alkaline-pectinase/H₂O₂ treatment in presence of PEG 400.     

Optimized production of lignolytic manganese peroxidase in immobilized cultures of <Emphasis Type="Italic">Phanerochaete chrysosporium</Emphasis>

Manganese peroxidase (MnP) is a key enzyme involved in the lignolysis of white-rot fungi. The purpose of this study is to investigate the effect of immobilization and culture conditions on MnP production in cultures of Phanerochaete chrysosporium grown on polyurethane foam. Higher concentrations of foam and lower levels of spore inoculums resulted in the formation of scattered mycelial pellets, increased autolysis of chlamydospore-like cells (a reservoir of MnP), and a higher activity of MnP. Even though MnP was a secondary metabolite, the addition of 5 times more glucose and diammonium tartrate, as carbon and nitrogen sources, resulted in a 4 fold increase in the dry cell mass. However, MnP activity decreased under these conditions to less than half, due to the formation of increasingly dense pellets and the inhibited lysis of chlamydospore-like cells.     

Differential sensitivity to cadmium in germinating seeds of three cultivars of faba bean (<Emphasis Type="Italic">Vicia faba</Emphasis> L.)

The reserve mobilization was analysed in germinating seeds of faba bean (Vicia faba) exposed to treatment with a toxic cadmium concentration for 4 days. When the behaviours of three cultivars were compared with regard to the germination rate, the following order of sensitivity to cadmium was observed: Aguadulce and Luz de otoño showed 59 and 19% of inhibition from controls, respectively, while no effect was observed in the case of the local Féverole. The growth of embryo radicle was also affected in the same pattern. The differential vulnerability to Cd stress cannot be correlated to shortage in water supply of cotyledons. However, Cd-treated germinating seeds of the most sensitive cultivar (Aguadulce) showed restriction in starch mobilization and decrease in availability of soluble sugars and free amino acids. Moreover, glucose, fructose and amino acids were markedly leaked into the germination medium at the expense of the growing embryonic axis during exposure to Cd. These results provide an indication of the way in which cadmium might impair seed germination.     

Photoperiodic time measurement in the aphid Megoura viciae

Megoura produces parthenogenetic virginoparae in long day conditions, gamic oviparae in short days. The nature of this photoperiodic response has been analysed by rearing parent apterae in a wide range of circadian and non-circadian light cycles. By varying the light and dark components independently in a two-component cycle it has been established that the time measuring function is associated primarily with the dark period. There is no evidence that an endogenous circadian oscillation is implicated: thus (a) the ‘short day’ response is abolished by ‘night interruptions’ positioned in the early or late night. But this bimodal response pattern remains unchanged when the duration of the ‘main’ photoperiod is varied from ca. 6 hr to at least 25·5 hr. The stability of the maxima within the scotophase is inconsistent with the ‘coincidence’ models of photoperiodic timing that have been proposed. It is suggested that the essential timing process operates on the hour-glass principle, beginning anew with the onset of each period of darkness; (b) night interruption experiments employing very long (up to 72 hr) scanned dark periods yielded response maxima explicable in terms of the hour-glass hypothesis but did not reveal any circadian relationship between the maxima.The ‘dark reaction’ comprises a sequence of four stages, definable by the effects of light. Stage 1, extending from dark hr 0 to ca. 2·5, is fully photoreversible: at the next dark period the entire timing sequence is repeated up to the 9·5 hr critical night length. Towards the end of stage 1 reversibility is gradually lost and after a light interruption the reaction is resumed from a later time equivalent than dark hr 0; the subsequent critical night length is therefore reduced. The extent of the photoreversal is related to light duration. The period of maximum light insensitivity (stage 2) is attained at the end of the fourth hour. From ca. dark hr 5 to just short of the critical night length light exerts an increasingly promotive action which favours the production of virginoparae. This dark process is not photoreversible. Stage 4, which begins at hr 9·5, marks the end of the timing sequence. Light will not then annul the non-promotive action of the previous long night.Light has three effects which are determined by its duration and position within the cycle. The two terminal effects, mentioned above, are associated with the interception of dark stages 1 and 3 by either short (1 hr) or longer photoperiods. Light also prepares or primes the dark period timer. Thus the critical length is increased, and timing accuracy lost, if the preceding photoperiod is less than ca. 6 hr. Light during stage 4 has a priming action but no terminal function. Repeated cycles are ‘read’ in various ways, depending on the cycle structure. For example, if light intercepts stage 3, a two-component cycle is interpreted as the overlapping sequence light/dark/light. One and the same photoperiod then acts terminally in respect of the preceding dark period and as a primer for the next dark period.There is also a mechanism for summing the promotive effects produced by repeated interruption of dark stage 3. With complex (four-component) cycles both halves of the same cycle may contribute. ‘Product accumulation’ falls below threshold if the frequency of presentation of a given promotive cycle is too low. This occurs if there are very long, relatively non-promotive dark components. Such cycles are accepted as ‘continuous darkness’.