Spontaneous and radiation-induced chromosomal instability and persistence of chromosome aberrations after radiotherapy in lymphocytes from prostate cancer patients

The aim of the study was to compare the spontaneous and ex vivo radiation-induced chromosomal damage in lymphocytes of untreated prostate cancer patients and age-matched healthy donors, and to evaluate the chromosomal damage, induced by radiotherapy, and its persistence. Blood samples from 102 prostate cancer patients were obtained before radiotherapy to investigate the excess acentric fragments and dicentric chromosomes. In addition, in a subgroup of ten patients, simple exchanges in chromosomes 2 and 4 were evaluated by fluorescent in situ hybridization (FISH), before the onset of therapy, in the middle and at the end of therapy, and 1 year later. Data were compared to blood samples from ten age-matched healthy donors. We found that spontaneous yields of acentric chromosome fragments and simple exchanges were significantly increased in lymphocytes of patients before onset of therapy, indicating chromosomal instability in these patients. Ex vivo radiation-induced aberrations were not significantly increased, indicating proficient repair of radiation-induced DNA double-strand breaks in lymphocytes of these patients. As expected, the yields of dicentric and acentric chromosomes, and the partial yields of simple exchanges, were increased after the onset of therapy. Surprisingly, yields after 1 year were comparable to those directly after radiotherapy, indicating persistence of chromosomal instability over this time. Our results indicate that prostate cancer patients are characterized by increased spontaneous chromosomal instability. This instability seems to result from defects other than a deficient repair of radiation-induced DNA double-strand breaks. Radiotherapy-induced chromosomal damage persists 1 year after treatment.     

Non-oncogenic T-region mutants ofAgrobacterium tumefaciens do transfer,T-DNA into plant cells

A new procedure for site-directed mutagenesis has been applied to the shooting and rooting loci of T-DNA of an octopine Ti-plasmid ofAgrobacterium tumefaciens. Mutants have been obtained which induced tumours that either developed shoots or produced more roots than normally observed. Double mutations, in which both types of T-DNA loci were affected, resulted in non-oncogenic strains. Indications have been obtained, showing that T-DNA coded oncogenic functions can be eliminated without affecting T-DNA transfer into plant cells.     

Detection of T-DNA transfer to plant cells by A. tumefaciens virulence mutants using agroinfection

Summary To test whether virulence mutants of Agrobacterium tumefaciens are capable of promoting T-DNA transfer into plant cells, a tandem array of Cauliflower Mosaic Virus (CaMV) DNA was cloned between T-region border sequences on a wide host range plasmid and introduced into various virulence mutants. The resulting strains were used to infect Brassica rapa cv. Just Right. This assay, recently referred to as agroinfection, is based on the appearance of viral symptoms following transfer of T-DNA to plant cells, and is shown to be at least 100 times more sensitive in detecting T-DNA transfer than tumour formation. Mutants in the loci vir A, B and G, which were avirulent on turnip, failed to induce virus symptoms. Of the two vir D mutants tested, neither induced tumours, but one was capable of inducing virus symptoms. Mutants in vir E, C and F, which induced respectively no, small and normal tumours on turnip, all induced virus symptoms.     

Ageing in Plants: Conserved Strategies and Novel Pathways

Abstract: Ageing increases chaos and entropy and ultimately leads to the death of living organisms. Nevertheless, single gene mutations substantially alter lifespan, revealing that ageing is subject to genetic control. In higher plants, ageing is most obviously manifested by the senescence of leaves, and recent molecular genetic studies, in particular the isolation of Arabidopsis mutants with altered leaf senescence, have greatly advanced our understanding of ageing regulation in plants. This paper provides an overview of the identified genes and their respective molecular pathways. Hormones, metabolic flux, reactive oxygen species and protein degradation are prominent strategies employed by plants to control leaf senescence. Plants predominantly use similar ageing-regulating strategies as yeast and animals but have evolved different molecular pathways. The senescence window concept is proposed to describe the age-dependent actions of the regulatory genes. It is concluded that the similarities and differences in ageing between plants and other organisms are deeply rooted in the evolution of ageing and we hope to stimulate discussion and research in the fascinating field of leaf senescence.     

Latency distributions in homogeneous bundles of myelinated axons

Using a very simple hypothesis concerning the length of the depolarized area during propagation of action potentials, distributions of latencies in bundles of myelinated axons have been derived. The internodal length, the number of nodes of Ranvier, the depolarized area and the variation in internodal length are the important parameters.To demonstrate the applicability of the derivation proposed here some examples taken from neurophysiological experiments are given.     

Mutations at the Asc locus of tomato confer resistance to the fungal pathogen Alternaria alternata f. sp. lycopersici

The fungal pathogen Alternaria alternata f. sp. lycopersici produces host-selective AAL-toxins that cause Alternaria stem canker in tomato. Susceptibility to the disease is based on the relative sensitivity of the host to the AAL-toxins and is controlled by the Asc locus on chromosome 3L. Chemical mutagenesis was employed to study the genetic basis of sensitivity to AAL-toxins and susceptibility to fungal infection. Following the treatment of seeds of a susceptible line with ethyl methanesulphonate (EMS), resistant M₂ mutants were obtained. Most plants with induced resistances showed toxin-sensitivity responses that were comparable to those of resistant control lines carrying the Asc locus. In addition, genetic analysis of the mutagenised plants indicated that the mutations occurred at the Asc locus. Furthermore, novel mutants were identified that were insensitive to the AAL-toxins at the seedling stage but toxin-sensitive and susceptible to fungal infection at mature stages. No AAL-toxin-insensitive insertion mutants were identified following a transposon mutagenesis procedure. Molecular mechanisms involved in host defence against A a. lycopersici are discussed.