Effect of distance,aggregation, and habitat on levels of seed predation for two mammal — dispersed neotropical rain forest tree species

The effect of seed aggregation and distance from conspecific trees on seed predation was experimentally examined for two neotropical tree species, Macoubea guianensis (Apocynaceae) and Pouteria sp. (Sapotaceae) in a lowland tropical rain forest in northeastern Peru. Results of these experiments are discussed in the context of the Janzen-Connell model (Janzen 1970; Connell 1971), which predicts decreased seed survival near parent trees due to either density-or distance-responsive mortality, and Howe's model (Howe 1989) which predicts that trees with seeds dispersed in clumps (aggregated) will not suffer density-dependent predation, and will have higher survival of seeds near the parent tree than other trees. We also examined whether predation on seeds of these species was affected by seed placement in or near 30-m-wide strips regenerating after clear-cutting. Both species appeared to be mammal-dispersed but differed in how frugivores handled seeds, seed size, overall fruit crop size, and gemination time. Neither of the two species studied appeared to suffer seed predation in a manner predicted by the Janzen-Connell model, and patterns of seed predation for only one of the species was similar to predictions of Howe's model. For neither species did seed predation along the edge of, or in the center of, regenerating clear cuts differ from predation 15 m into the primary forest. For Pouteria, seed predation in and near regnerating strips was significantly greater than around forest trees, but the opposite pattern held for Macoubea. Overall, seed predation was much greater on Macoubea. The difference in seed predation for these two species was most likely a result of differences in the types of seed predators that attacked these two species.     

The cyanobacterial genome contains a single copy of the ffh gene encoding a homologue of the 54 kDa subunit of signal recognition particle

Cyanobacteria possess thylakoid membranes that differ in their protein composition from the cytoplasmic membrane. To study possible pathways of protein targeting to these membranes, we have investigated whether or not cyanobacteria have a homologue or homologues of the signal recognition particle-like chaperone Ffh. We have amplified a fragment of ffh by polymerase chain reaction and established that ffh is present as a single copy in the genomes of three cyanobacterial species. We have cloned and sequenced ffh from Synechococcus sp. PCC7942 and predict that Ffh functions as a ribonucleoprotein in cyanobacteria and chloroplasts.     

Genetically stable cell lines of cucumber for the large-scale production of diploid somatic embryos

For the initiation of embryogenic cucumber ( Cucumis sativus L.) cell lines, from excised radicles, directly in liquid medium, the culture regime, explant density and type and concentration of hormones were adjusted so that pro-embryogenic masses (PEMs) were formed within about 8 weeks. The established cucumber cell lines were maintained tor several years without loss of embryogenic and genetic stability. The ploidy level of somatic embryos from different cucumber eell lines was either diploid or tetraploid and depended on the ploidy level of Ihe cell line. Cucumber cell lines that produced only diploid embryos were obtained by selecting completely diploid explant material and growing it in the dark during the initiation phase. Mixoploid explains could lead to tetraploid or mixoploid ceil lines. Isolation and additional selection and subculturing of single PEMs resulted in either completely diploid or tetraploid cell lines, indicating that all cells of individual PEMs are either diploid or tetraploid. The ernbryogenic cucumber cell Imes, differing only in ploidy level, were indistinguishable in growth rate and embryogetiic potential and were genetically stable over several years.     

Tn5 insertion mutants of Pseudomonas sp. 267 defective in siderophore production and their effect on clover (Trifolium pratense) nodulated with Rhizobium leguminosarum bv. trifolii

Pseudomonas sp. strain 267 isolated from soil promoted growth of different plants under field conditions and enhanced symbiotic nitrogen fixation in clover under gnotobiotic conditions. This strain produced pyoverdine-like compound under low-iron conditions and secreted vitamins of the B group. The role of fluorescent siderophore production in the beneficial effect of strain 267 on nodulated clover plants was investigated. Several non-fluorescent (Pvd^-) Tn5 insertion mutants of Pseudomonas sp. strain 267 were isolated and characterized. The presence of Tn5 insertions was confirmed by Southern analysis of EcoRI digested genomic DNA of each derivative strain. The siderophore-negative mutants were compared to the parental strain with respect to their growth promotion of nodulated clover infected with Rhizobium leguminosarum bv. trifolii 24.1. We found that all isolated Pvd^- mutants stimulated growth of nodulated clover plants in a similar manner to the parental strain. No consistent differences were observed between strain 267 and Pvd^- derivatives strains with respect to their plant growth promotion activity under gnotobiotic conditions.Dr Deryto died in august 1994     

The effect of reduced phytoalexin production on the resistance of upland cotton (Gossypium hirsutum) to verticillium and fusarium wilts

The effect on disease development of inhibiting the production of the sesquiterpenoid phytoalexin hemigossypol (HG) in cotton resistant to both verticillium and fusarium wilts was investigated. Inhibition was achieved by treating the plants with the sodium salt of compactin, a competitive inhibitor of hydroxy-methylglutaryl (HMG) CoA reductase. Compactin treatment (150 μg litre^-1) reduced HG production by a mean of 48%. The enzyme inhibitor did not mimic symptoms in uninfected plants or significantly reduce the ability of the conidia of either Fusarium oxysporum f.sp. vasinfectum or Verticillium dahliae to germinate. Treatment of infected plants with compactin resulted in a breakdown of resistance to verticillium wilt but not to fusarium wilt. These results support the view that HG production is the primary mechanism of resistance to verticillium wilt, but not to fusarium wilt.     

有机硅橡胶固定化细胞进行的生物转化

有机硅橡胶固定化细胞进行的生物转化潘冰峰,戴学倩,冯青,李祖义（中国科学院上海有机化学研究所,２０００３２）关键词硅橡胶;白地霉;固定化细胞;生物转化近年来,有机化学领域的一个重要进展是用酶或微生物进行生物转化反应。其中研究和应用较多的是碳基还原,特...     

In Vitro Culture of Phytomonas Sp. Isolated from Euphorbia characias. Metabolic Studies by 1H NMR

ABSTRACT. We describe the in vitro culture of Phytomonas species isolated from Euphorbia characias . The best choice between tested media was SDM-79, in which promastigotes, after 6 days of culture, reached cell densities as high as 4 × 10⁷ cells/ml. Cells growing in LIT or MTL medium showed longer division times and lower cell densities. We succeeded in obtaining Phytomonas sp. amastigote and spheromastigote forms in modified GRACE's medium, yielding transformation rates of up to 70%. Electron microscopy studies were performed in order to characterize the ultrastructural features of these forms obtained in vitro. On the other hand, metabolic studies based on qualitative (nuclear magnetic resonance spectroscopy) and quantitative metabolic methods (enzymatic assays) showed that promastigote forms secreted mainly ethanol, acetate, glycine, glycerol, piruvate and succinate in SDM-79 medium, whereas the major metabolites found after transformation in modified Grace's medium were ethanol, acetate, glycine, piruvate and smaller amounts of glycerol.     

Impact of grazing on vegetation dynamics in former ricefields

Abstract. In the Rhône delta, Juncus gerardi and Scirpus maritimus are often the dominant species in abandoned rice fields which are artificially flooded in early spring to improve forage production. Under these conditions they occur either in mixed communities, or form monospecific stands. Monitoring the vegetation dynamics in quadrats located in six abandoned rice fields artificially flooded from November to April confirmed the important role of grazing. In ungrazed plots, communities dominated by Scirpus maritimus mixed with Juncus gerardi developed fast. After 42 months of management Scirpus maritimus had established in nearly all quadrats and continued to expand, whereas Juncus gerardi had started to decline. In grazed plots Juncus gerardi alone dominated and continued to increase in cover up to the 42nd month. Scirpus maritimus established at low densities mainly in quadrats where Juncus gerardi was initially absent. Introduction of seeds of Scirpus maritimus in communities of Juncus gerardi under controlled conditions demonstrated the existence of the phenomenon of preemption. The increase in cover of Juncus gerardi suggests that the preemption of Juncus gerardi over Scirpus maritimus plays a more pronounced role in the field in the presence of grazing.     

Isolation and identification of (2S)-2-amino-5-chloro-4-hydroxy-5-hexenoic acid from anAmanita of the sectionRoanokenses (Amanitaceae)

A chlorine-containing non-protein amino acid which was recently discovered from the fruit bodies ofAmanita gymnopus (2S)-2-amino-5-chloro-4-hydroxy-5-hexenoic acid, was isolated and crystallized for the first time from the fruit bodies of an unknown member ofAmanita belonging to the sectionRoanokenses, subsectionSolitariae. The results of elementary analyses, determination of optical rotations,¹H- and¹³C-NMR-spectra, and some chemical reactions supported an earlier proposed structure.Part 24 in the series Biochemical studies of nitrogen compounds in fungi. for Part 23, see Hatanaka, S. I. et al. 1994. this journal35: 391–394.     

Discrepancies between MIC and MLC values of amphotericin B against isolates ofAspergillus species

There is little information addressing the phenomena of discrepancy between minimal inhibitory concentrations (MIC) and minimal lethal concentrations (MLC) values of amphotericin B (AMB) to clinical isolates of fungi. This study assessed in vitro activity of AMB against 70 clinical isolates of aspergilli: 30 strains ofAspergillus fumigatus, 20 strains ofAspergillus flavus and 20 strains ofAspergillus niger. Susceptibility tests were accomplished using a macro broth dilution procedure, with special emphasis on ascertainment of MLCs. AMB exhibited low MIC values against all clinical isolates. While we did not identify any AMB resistant isolates among 70Aspergillus spp. studied as judged by MIC levels, analysis of the data demonstrated a clear discrepancy between the MIC and MLC levels of AMB obtained against clinical isolates ofAspergillus spp. The MLC values of AMB were significantly higher than the MIC values with MIC 50 and MIC 90 of 0.29 and 0.5 µg/ml, respectively, at the second reading time, and MLC 50 and MLC 90 of 2.31 and 9.24 µg/ml, respectively (p<0.001). Additionally, minimal lethal concentrations in 36/70 (51%) of aspergillal isolates studied produced drug concentrations above those which can usually be sustained in patient plasma or tissue.