The Effect of Cytokinins on Vitrification in Melon and Carnation

The influence of exogenous cytokinin on vitrification of melonand carnation buds grown in vitro was assessed. In melon, theanatomical traits of vitrification were found to be similarto those previously described for carnation grown on a highconcentration of auxin. In carnation, the plantlets treatedwith high cytokinin concentrations became bushy but the anatomicalstructure remained normal. The relation of cytokinin and vitrificationis discussed. Cucumis melo L., Dianthus caryophyllus L., vitrified plantlets, habituation, cytokinin     

Heat-resistant Bacteria in Pasteurized Whole Egg

Samples of egg melange taken from an egg packing station contained an average of 7·3 x 10⁴ organisms/ml which survived laboratory pasteurization at 65°C for 3 min. Many of the organisms surviving pasteurization were found to be coryneform bacteria related to Microbacterium lacticum which could be differentiated into several groups. The remainder were a miscellaneous collection of unidentified cocci and coccobacilli and some Bacillus spp. The coryneform bacteria were shown to be the most heat-resistant isolates with negligible loss of viability after 60 min at 65°C, At least two of the representative strains were very heat-resistant, 0·01% surviving 20 and 38 min at 80°C in phosphate buffer at pH 7·1. Growth tests showed that none of the isolates grew at 5°C after 10 d incubation but those capable of growing most rapidly at 10° and 15°C were also the most heat-resistant. Such strains had a doubling time at 15°C of between 6 and 8 h in whole egg. Freezing the coryneform bacteria in liquid whole egg at –18°C had negligible effect on viability or heat-resistance at 65°C.     

Cytological evidence of natural hybridization in Brachiaria brizantha Stapf (Gramineae)

Two accessions of Brachiaria brizantha under cytological analysis showed 2 n  = 5x = 45 chromosomes. Pentaploidy probably resulted from natural hybridization between two species that were not closely related: an apomictic tetraploid male (2 n  = 4x = 36), and a sexual diploid female (2 n  = 2x = 18). The lack of affinity between genomes was clearly indicated by asynchrony during meiosis. The haploid genome ( n  = 9) showed unique behaviour, remaining univalent during prophase I and metaphase I, and undergoing sister-chromatid segregation and lagging at anaphase I. The laggard genome did not always reach the poles in time to be included in the telophase nucleus. However, when the inclusion was effective, this genome was distributed peripherally, changing the otherwise spherical nucleus shape. In the second division, the haploid genome behaved similarly, but as there was sister-chromatid segregation during the first division, the chromatids were slow to reach the poles, forming several micronuclei at telophase II. The two accessions were characterized as allo-autopentaploids, with the tetraploid genome (2 n  = 4x = 36) designated as B (from B. brizantha ) and the haploid genome as X, representing a species with a distinct genome having little affinity with the B genome. Thus, the hybrids' genome composition is represented by BBBBX. By comparing their meiotic behaviour with that observed in synthetic hybrids between B. brizantha and B. ruziziensis analysed previously, B. ruziziensis is the putative diploid sexual parent species in these pentaploid accessions.  © 2006 The Linnean Society of London , Botanical Journal of the Linnean Society , 2006, 150 , 441–446.     

Chromosome numbers and meiotic analysis in the pre-breeding of <Emphasis Type="BoldItalic">Brachiaria decumbens</Emphasis> (Poaceae)

A total of 44 accessions of Brachiaria decumbens were analysed for chromosome count and meiotic behaviour in order to identify potential progenitors for crosses. Among them, 15 accessions presented 2n = 18; 27 accessions, 2n = 36; and 2 accessions, 2n = 45 chromosomes. Among the diploid accessions, the rate of meiotic abnormalities was low, ranging from 0.82% to 7.93%. In the 27 tetraploid accessions, the rate of meiotic abnormalities ranged from 18.41% to 65.83%. The most common meiotic abnormalities were related to irregular chromosome segregation, but chromosome stickiness and abnormal cytokinesis were observed in low frequency. All abnormalities can compromise pollen viability by generating unbalanced gametes. Based on the chromosome number and meiotic stability, the present study indicates the apomictic tetraploid accessions that can act as male genitor to produce interspecific hybrids with B. ruziziensis or intraspecific hybrids with recently artificially tetraploidized accessions.     

The Relationship between Stimulus Intensity and Oriented Phototactic Response (Topotaxis) in Chlamydomonas

Two techniques have been used to study the quantitative relationship between stimulus intensity and oriented phototactic response (topotaxis) in Chlamydomonas. The net response of a cell population was monitored photometrically and was recorded continuously against time. The responses of individual cells were observed through a microscope and their swimming tracks were recorded on film. The net response of the population is positive at low stimulus intensity and negative at high intensity. The direction of response can be reversed within two seconds by raising or lowering the intensity. The intensity-response curve for phototaxis is similar to the dose-response curve for phototropism. The net response has no distinct threshold; it increases linearly with log intensity; then it decreases and finally becomes negative. The individual-cell studies reveal that the intensity-dependent increase in net topotactic response is due primarily to an increase in the number of cells responding and in the directness of their swimming path. As stimulus intensity is raised, the swimming path becomes increasingly well-aligned with the stimulus beam, whether net response is positive throughout the intensity range tested, negative throughout that range, or changing from positive to negative. Changes in swimming rate do not contribute significantly to the intensity-dependent changes in net response. Swimming rate shows virtually no change throughout the intensity range of positive topotaxis and shows only a small increase in the negative range. However, a transient decrease in swimming rate (stop response) is often observed at the onset of stimulation. The implications of these results for the orientation mechanism are discussed.     

THE DISTRIBUTION OF GROUP D STREPTOCOCCI IN CATTLE AND SHEEP

Numbers and types of Lancefield group D streptococci have been determined in samples from the colons of 17 cattle and 9 sheep. Mean total streptococcal counts of 8 × 10⁴/g in cattle and 2 × 10⁶/g in sheep were obtained. Streptococcus bovis was found in every sample and was the predominant species in 15 of the cattle and 6 of the sheep. Other group D streptococci ( Strep. faecalis, Strep. faecium and Strep. durans ) were rare in cattle, but in sheep they formed a significant proportion of the population. Of 60 Strep. faecium, Strep. durans and related strains, 51 fermented raffinose. Many of the strains of Strep. faecium were also atypical in that they fermented sorbitol and appreciably reduced tetrazolium in broth at pH 6.0.
Strep. bovis remained the predominant streptococcus in faeces samples from 4 dairy cows when they were tested again after an interval of 17 and 18 months.     

THE EFFECT OF THE TETRACYCLINE COMPOUNDS ON THE STORAGE LIFE AND MICROBIOLOGY OF CHILLED EVISCERATED POULTRY

SUMMARY: Chlortetracycline, oxytetracycline and tetracycline, incorporated at 10 p/m in the ice slush used for cooling, were equally efficient in extending the storage life of eviscerated poultry which was subsequently frozen, thawed and stored at 1°. There was complete correlation between the sensory assessment of 'off'odour and the total numbers of micro-organisms present when these were determined by taking bulk samples of skin from the area under the wing and of the surface tissue of the visceral cavity near the vent. Direct microscopical counts confirmed that the latter area was the most heavily contaminated part of the visceral cavity. Non-pigmented strains of Pseudomonas were the main spoilage organisms of untreated chickens but Achromobacter strains and yeasts were responsible for the spoilage of the chlortetracycline treated chickens. Fluorescence was only observed in spoiled chickens where pigmented strains of Pseudomonas occurred in significant numbers. Spoilage in both control and antibiotic treated poultry was accompanied by a rise in pH in the contaminated muscles, but for various reasons this change could not be used as a direct measure of the extent of the microbial contamination.