Synaptic patterns of rye B chromosomes. II. The effect of the standard B chromosomes on the pairing of the A set

In order to elucidate the possible effects of rye B chromosomes (Bs) on synapsis and metaphase-I associations of the A set, a comparative study between pachytene and metaphase-I-cells of rye plants carrying different numbers of Bs (0–8) has been carried out. The number of Bs was found to be positively correlated with the frequency of synaptic irregularities of the A set, i.e. multivalents and foldback pairing, and with the frequency of pachytene interlockings. It is proposed that interlockings are the origin of these irregularities because both appeared in close proximity in many nuclei. Examples of A-B pairing are described. The frequency of synaptic abnormalities seems to be unrelated to the mean of A chromosome-bound arms at metaphase I.     

CHARACTERIZATION AND BIOLOGICAL IMPLICATIONS OF SCYTONEMIN,A CYANOBACTERIAL SHEATH PIGMENT1

Scytonemin, the yellow-brown pigment of cyanobacterial (blue-green algal) extracellular sheaths, was found in species thriving in habitats exposed to intense solar radiation. Scytonemin occurred predominantly in sheaths of the outermost parts or top layers of cyanobacterial mats, crusts, or colonies. Scytonemin appears to be a single compound identified in more than 30 species of cyanobacteria from cultures and natural populations. It is lipid soluble and has a prominent absorption maximum in the near-ultraviolet region of the spectrum (384 nm in acetone; ca. 370 nm in vivo) with a long tail extending to the infrared region. Microspectrophotometric measurements of the transmittance of pigmented sheaths and the quenching of ultraviolet excitation of phycocyanin fluorescence demonstrate that the pigment was effective in shielding the cells from incoming near-ultraviolet-blue radiation, but not from green or red light. High light intensity (between 99 and 250 μmol photon · m^?2· S^?1, depending on species) promoted the synthesis of scytonemin in cultures of cyanobacteria. In cultures, high light intensity caused reduction in the specific content of Chl a and phycobilins, increase in the ratio of total carotenoids to Chl a, and scytonemin increase. UV-A (320–400 nm) radiation was very effective in eliciting scytonemin synthesis. Scytonemin production was physiological and not due to a mere photochemical conversion. These results strongly suggest that scytonemin production constitutes an adaptive strategy of photoprotection against short-wavelength solar irradiance.     

Poplar (Populus nigra L.) plants transformed with aBacillus thuringiensis toxin gene: insecticidal activity and genomic analysis

Insect-resistant poplar (Populus nigra L.) plants have been produced by infecting leaves withAgrobacterium tumefaciens strains carrying a binary vector containing different truncated forms of aBacillus thuringiensis (B.t.) toxin gene under a duplicated CaMV 35S promoter. Putative transgenic plants were propagated by cuttings at two experimental farms (in Beijing and Xinjiang, China). At 2–3 years after transformation, 17 of them were selected on the bases of insect-tolerance and good silvicultural traits, and evaluated for insect resistance, for the presence of theB.t. toxin DNA fragment (Southern blots and PCR) and for the expression of the transgene (western and northern blots). Somaclonal variation, as suggested by the appearance of permanent changes in the shape of the leaves, was also investigated with molecular tools (RFLP (restriction fragment length polymorphism), RAPD (random amplified polymorphic DNA) and microsatellite DNA).Bioassays withApochemia cineraius andLymantria dispar on the leaves of the selected clones showed different and, in some cases, high levels of insecticidal activity. The molecular analysis demonstrated integration and expression of the foreign gene. Somatic changes were correlated to extensive genomic changes and were quantified in dendrograms, in terms of genomic similarity. The analysis of control plants suggested that genomic changes were correlated to thein vitro culture step necessary forA. tumefaciens-mediated gene transfer, rather than to the integration of the foreign genes.Three transgenic clones (12, 153 and 192), selected for insect resistance, reduced morphological changes and promising silvicultural traits, are now under large-scale field evaluation in six different provinces in China.     

The effect of B chromosomes on fitness components inAegilops speltoides Tausch

The effect of B chromosomes (Bs) on various components of vigour and fertility inAegilops speltoides was studied. We designed three types of synthetic populations. In the first type we compared plants from the localities Haifa (which has Bs in nature) and Ashkelon (which has not). Non significant differences were found between the plants from both populations, and between B carriers and non carriers among Haifa individuals. In the second synthetic population we compared 0B, 1B, 2B, 3B and 5B plants from Haifa. We found that vigour variables were not affected by the presence of Bs, while fertility variables were significantly correlated with B number, in such a way that 1B plants produce more grains per plant than any other constitution, while 5Bs produce a remarkable deleterious effect. In the third type of synthetic populations we compared plants with 0B and 1B, 0B and 2B, 0B and 3B, and 0B and 5B. In this case we also found that 1B plants were the most fertile, but the variation of reproductive fitness was higher from plot to plot within the same B class than among B classes. We conclude that the effect of B chromosomes on the fitness variables that we have estimated is close to neutrality in this species. We discuss the relation between the strength of the mechanism of accumulation and the deleterious effects of B chromosomes.     

Interferon antibodies in patients with infectious diseases

Interferons (IFNs) are generally recognized as the most important therapeutic agent in some infectious diseases such as chronic hepatitis B and C. Since the early clinical trials it was documented that the therapeutic use of IFNs could be complicated by the development of antibodies able to neutralize or to bind to the IFN molecule. After several years of research it is now widely accepted that the presence of circulating anti-IFN antibodies may affect the response to IFN. Here we summarize what is currently know on the clinical significance of antibodies to IFN in IFN-treated viral diseases patients.     

Isolation of an evolutionarily conserved epidermal growth factor receptor cDNA from human A431 carcinoma cells

Complementary DNA corresponding to total poly(A)+-RNA from the human A431 epidermoid carcinoma cell line was cloned in the phage expression vector lambda gt 11. An epidermal growth factor (EGF) receptor cDNA clone was obtained by screening of the expression library with a rabbit polyclonal antibody (IgG), raised to the purified A431 EGF receptor, in combination with [125I]protein A of S. aureus. The cloned cDNA was able to select, by hybridization, messenger RNA which was translated in Xenopus oocytes and yielded an immunoprecipitable EGF receptor protein of Mr = 160,000. The insert of this cDNA (phEGFR-1), is approximately 880 base pairs in length and encodes the carboxyterminal portion of the EGF receptor protein. Its sequence is evolutionarily conserved among vertebrates as shown by hybridization to unique chromosomal DNA sequences from human, baboon, dog, rat, mouse and frog.     

Determination of the minimal inhibitory concentration of Amphotericin B and Miconazole for 21 strains of Aspergillus

The susceptibility of 21 strains ofAspergillus (11 ofA. fumigatus, 8 ofA. niger, and 2 ofA. flavus) isolated from human pathologic specimens to Amphotericin B and Miconazole has been comparatively studied. Determination of the minimal inhibitory concentration of both drugs in a liquid medium showed a noticeably variability for the different strains. The values obtained for Amphotericin B varied between 0.25g/ml (2 strains) and 1.25g/ml (5 strains) after 48 hours, and between 1.25g/ml (1 strain) and 50g/ml (1 strain) after 10 days. For Miconazole the results varied between 0.1g/ml (1 strain) and 25g/ml (1 strain) after 48 hours of incubation, and between 0.5g/ml (5 strains) and > 100g/ml after 10 days. The variability of these results indicates the usefulness of carrying ourin vitro sensitivity studies whenever it is possible.     

An in situ assay for induced diphtheria-toxin-resistant mutants of diploid human fibroblasts

The sensitivity of diploid human fibroblasts to the cytotoxic effects of diphtheria toxin (DT) depended on the cell growth status. Exponentially growing cells treated with 10^?3-1 lethal flocculating units (LF) of DT/ml for 4 days survived with a frequency of 4 × 10^?4. However, the DT-resistant phenotype of colonies isolated under these conditions was not stable. When the growth of the cells had been arrested by confluence or deprivation of serum growth factors prior to treatment with DT (4 days, 10^?3-0.6 LF/ml), the survival decreased to 2 × 10^?6 and the resistance of isolated colonies was stable. An in situ assay for induced DT-resistant mutants was developed in order to avoid problems associated with the possible reduced viability of the mutants relative to that of wild-type cells. A reproducible and linear dose response was obtained for the induction of DT-resistant mutants by ethylnitrosourea. The mutants were induced with high frequency by this compound (e.g., 10^?3 mutants/viable cell at a 37% survival dose); complete expression of the mutant phenotype occurred after 6 generations of growth under nonselective conditions. Isolated mutant colonies showed stable resistance to DT and were cross-resistant to Pseudomonas aeruginosa exotoxin A.