Homologies to chloroplast DNA in the nuclear DNA of a number of Chenopod species

Summary Sequences homologous to chloroplast (ct)DNA have been found in nuclear DNA in five species of the Chenopodiaceae, extending the earlier observations of promiscuous DNA in Spinacia oleracea (Timmis and Scott 1983). Using the 7.7 kbp spinach ctDNA Pst I fragment as a hybridization probe, several separately located homologies to ctDNA were resolved in the nuclear DNA of Beta vulgaris, Chenopodium quinoa, and Enchylaena tomentosa. In Chenopodium album and Atriplex cinerea the major region of homology was to a nuclear Eco RI fragment (6 kbp) indistinguishable from that in ctDNA. These homologies may therefore involve larger tracts of ctDNA because the same restriction sites are apparently retained in the nucleus. This suggests that in these latter two species there is a contrasting, more homogeneous arrangement of ctDNA transpositions in the nucleus.     

Heteroduplex molecules formed between allelic sequences cause nonparental RAPD bands.

Primers (10-mers) of random sequence were used to amplify RAPD bands from genomic DNA of an F1 strain of flax rust (Melampsora lini) and its two parent strains. One primer out of 160 tested was unusual in that it amplified a product from F1 DNA that was not amplified from either parental DNAs. The same primer also generated two RAPD bands that segregated as codominant alleles amongst F2 progeny. The nonparental band was only generated from DNAs of F2 individuals that were heterozygous for these two allelic sequences. Sequence analysis of the two RAPD alleles demonstrated greater than 99% sequence identity, although the larger allele possessed an additional 38bp relative to the smaller. Mixing of the two allelic sequences followed by denaturation and annealing in the absence of polymerase activity resulted in the formation of the nonparental band. Thus the nonparental band present in some RAPD reactions consisted of a heteroduplex molecule formed between two allelic sequences of different size. These data demonstrate that heteroduplex molecules formed between allelic RAPD products are a potential source of artifactual polymorphism that can arise during RAPD analysis.     

The effect of experimental induced hypocalcaemia on uterine activity in the sow during parturition and post-partum

Uterine activity was measured by monitoring intrauterine pressure changes using ballon-tipped catheters placed in the lumen. An infusion rate of Na(2)EDTA of 35 mg/Kg/h gave a chelation rate equivalent to the rate of calcium mobilisation, and when infused at a level greater than this, resulted in a reduction in plasma calcium concentrations and a concomitant reduction in uterine activity. In three of the four sows infused intrapartum, there was complete cessation of uterine activity; however, plasma calcium concentrations of less than 6 mg 100 ml resulted in a reduction in uterine activity at this stage of parturition. The uterus of the sow post-partum appeared to be more sensitive to the effects of hypocalcaemia with reduced uterine activity when plasma calcium concentrations fell below 8.2 mg 100 ml and complete cessation of activity between 6 and 7 mg 100 ml . Although there was evidence of a delay in the expulsion of piglets in the hypocalcaemic sows, there was no evidence of an increased number of stillborn piglets compared with the two control sows.     

Analysis of plastid DNA-like sequences within the nuclear genomes of higher plants

A wide-ranging examination of plastid (pt)DNA sequence homologies within higher plant nuclear genomes (promiscuous DNA) was undertaken. Digestion with methylation-sensitive restriction enzymes and Southern analysis was used to distinguish plastid and nuclear DNA in order to assess the extent of variability of promiscuous sequences within and between plant species. Some species, such as Gossypium hirsutum (cotton), Nicotiana tabacum (tobacco), and Chenopodium quinoa, showed homogenity of these sequences, while intraspecific sequence variation was observed among different cultivars of Pisum sativum (pea), Hordeum vulgare (barley), and Triticum aestivum (wheat). Hypervariability of plastid sequence homologies was identified in the nuclear genomes of Spinacea oleracea (spinach) and Beta vulgaris (beet), in which individual plants were shown to possess a unique spectrum of nuclear sequences with ptDNA homology. This hypervariability apparently extended to somatic variation in B. vulgaris. No sequences with ptDNA homology were identified by this method in the nuclear genome of Arabidopsis thaliana.      

Distinction between Infection and Rejection in Lung Transplantation

In distinguishing between infection and rejection after human lung transplantation clinical and radiological features were unhelpful, and even confusing. However, incipient rejection could be predicted and distinguished from infection by monitoring alterations in lymphocyte activity by the rosette inhibition test. Earlier prediction seems possible by detecting circulating lung-binding antibody. The ability to detect changes in the immunological status of a patient, even before clinical deterioration, has fundamental implications for the management of patients after transplantation.     

Durable resistance to wheat stem rust needed

The recent outbreak of a new wheat stem rust race capable of parasitizing many commercial wheat cultivars highlights the need for durable disease resistance in crop plants. More advanced breeding approaches using quantitative disease resistance genes and resistance gene pyramids are being used to combat wheat stem rust and other diseases, though widespread adoption of these breeding methodologies is needed to maintain resistance efficacy. Advances in understanding the molecular basis of plant disease resistance at both host and nonhost levels offers further possibilities for stem rust resistance using biotechnological approaches. However, truly durable resistance to wheat stem rust and other phytopathogens seems an unlikely prospect in the face of continually evolving pathogen populations.