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A R Walker

Publications and source records attributed to A R Walker.

At least 55 records · Page 3Linked to original sources
PubMed1999

Allele-specific interactions between ttg and gl1 during trichome development in Arabidopsis thaliana.

Trichome development in Arabidopsis thaliana is a well-characterized model for the study of plant cell differentiation. Two genes that play an essential role in the initiation of trichome development are GL1 and TTG. Mutations in either gene prevent the initiation of most trichomes. The GL1 gene encodes a myb-related transcription factor. Mutations in TTG are pleiotropic, affecting anthocyanins, root hairs, and seed coat mucilage in addition to trichomes. Six ttg alleles were examined and shown to form a hypomorphic series. The severity of all aspects of the ttg phenotype varied in parallel in this allelic series. The weakest allele, ttg-10, causes frequent clusters of adjacent trichomes, suggesting a role for TTG in inhibiting neighboring cells from choosing the trichome fate. This allele results from a mutation in the 5'-untranslated region of ttg and creates an out-of-frame upstream AUG codon. The ttg-10 allele shows several unusual genetic interactions with the weak hypomorphic gl1-2 allele, including intergenic noncomplementation and a synthetic glabrous phenotype. These interactions are specific for the gl1-2 allele. The implication of these results for current models of trichome development is discussed.

Alleles↗
PubMed1999

Pattern of cancer in Indian patients hospitalized in Durban, South Africa.

In emigrants from less to more developed countries, consequent changes in environmental factors are associated, inter alia, with changes in occurrences of the chronic diseases of lifestyle. In South Africa, most immigrants from India arrived in the early 1900s. To learn of the current pattern of cancer in the descendants of these people, enquiries were made on several series of patients admitted to RK Khan Hospital in Durban. The results were then compared with those of patients admitted to Ambojogai Hospital, North West India, the ancestral home of the majority of South African Indians. The most prominent differences were the lower percentages in South African Indians in respect of cancers of the mouth/pharynx in both sexes and of cervical cancer, and their considerably higher percentages, principally in the cases of stomach cancer in both sexes, of prostate cancer in males and of breast cancer in females. Discussion of risk factors indicates that in such populations there could be some control over the rises in some cancers, and on reductions in others. However, endeavours at prevention are hindered not only by the lack of knowledge prevailing, but also by their general indifference; likewise, this is the case with western populations.

Diet↗
PubMed1999

The TRANSPARENT TESTA GLABRA1 locus, which regulates trichome differentiation and anthocyanin biosynthesis in Arabidopsis, encodes a WD40 repeat protein.

The TRANSPARENT TESTA GLABRA1 (TTG1) locus regulates several developmental and biochemical pathways in Arabidopsis, including the formation of hairs on leaves, stems, and roots, and the production of seed mucilage and anthocyanin pigments. The TTG1 locus has been isolated by positional cloning, and its identity was confirmed by complementation of a ttg1 mutant. The locus encodes a protein of 341 amino acid residues with four WD40 repeats. The protein is similar to AN11, a regulator of anthocyanin biosynthesis in petunia, and more distantly related to those of the beta subunits of heterotrimeric G proteins, which suggests a role for TTG1 in signal transduction to downstream transcription factors. The 1.5-kb TTG1 transcript is present in all major organs of Arabidopsis. Sequence analysis of six mutant alleles has identified base changes producing truncations or single amino acid changes in the TTG1 protein.

Alleles↗
PubMed1999

Health and cancer prevention: implications of the knowledge and beliefs of 15-16 year old school pupils in South Africa.

The objective was to collect information from African and white pupils aged 15-16 years on their knowledge of and attitudes towards cancer, and their understanding of health-related behaviours in relation to their future experience. Questionnaires were completed by a series of 338 African and 378 white pupils in suburban secondary schools. African and white pupils knew most about lung cancer, and had some knowledge of skin and breast cancers. Smoking was seen by most as the chief cause of the disease. Half of both groups perceived a high intake of vegetables and fruit as protective. Television and printed media were the most important sources of information. The children in both groups were more anxious about unemployment and violence, and also, among African children, about AIDS, than about future ill-health. Thus, health was not perceived by many as the most important goal in life. Discussion indicates that white adolescents and also white adults, with more advanced understanding of cancer causation, make very limited use of their knowledge, dietary and non-dietary, to avoid the disease. In brief, level of cancer knowledge has very limited implications. Although young Africans in the course of their transition are very unlikely to seek to diminish their risk of cancer, there must be no lessening of urgent warnings and advice through the media on the avoidance of the disease.

Black or African American↗
PubMed1999

Iron overload in Sub-Saharan Africa: to what extent is it a public health problem?

Excessive deposition of Fe in the organs and tissues of Sub-Saharan Africans was first described in South Africa in 1929. Fe overload, or siderosis, was initially attributed to infections and to metallic poisoning (Cu, Sn, Zn), and then to malnutrition. In 1953 it was hypothesized that it was due primarily to excessive Fe intake derived from foods and drinks prepared in Fe vessels. Recently, in 1992 it was advanced that a gene distinct from any HLA-linked locus may also play a role. As to sequelae, in early research on series of hospital patients, the condition was linked to scurvy, osteoporosis, diabetes, cirrhosis, and latterly, to hepatocellular cancer and tuberculosis. Accordingly, many have concluded that Fe overload is responsible for considerable morbidity and mortality, that adventitious Fe intake should be reduced, and that phlebotomy be recommended for those severely affected. However, there are numerous limitations in the evidence. There are also problems in interpretation, since levels of Fe in the serum are affected additionally by a variety of factors: infection, inflammation, certain cancers and alcohol intake. These considerations complicate attempts to assess to what extent the associations described denote causation, and whether Fe overload has significant ramifications for ill in the general African population. While the adverse sequelae of overload may be less of significance than many believe, the precise pathogenicity of the phenomenon will remain uncertain until further investigations, including prospective studies, are undertaken.

Adult↗
PubMed1998

Natural prevalence of infection with Ehrlichia (Cytoecetes) phagocytophila of Ixodes ricinus ticks in Scotland.

Ixodes ricinus nymphs and adults were collected from vegetation and from sheep at four sites in Scotland typical of areas endemic for tick-borne fever in sheep caused by infection with Ehrlichia (Cytoecetes) phagocytophila (Rickettsiales). The great majority of ticks examined was from woodland sites adjacent to sheep farms where there was a high probability of them feeding on roe deer (Capreolus capreolus) in a non-domestic focus of infestation and infection. Ticks were examined for infection by five methods. Batches of ticks were examined either by feeding on susceptible sheep or by feeding on rabbits and then prepared as stabilate which was inoculated into susceptible sheep. The sheep were monitored for clinical signs of tick borne fever. Batches of ticks were examined by polymerase chain reaction for Ehrlichia phagocytophila. Salivary glands were dissected out and stained by the Feulgen method to detect Ehrlichia masses, and were examined by indirect fluorescent antibody test. Each of the methods detected infection in ticks and the prevalence of infection in nymphs with the various methods ranged from >0.25% to 2.0%. Small samples of adults examined by Feulgen staining of salivary glands indicated infection prevalences of 2.1% in males and 1.6% in females. It is considered that these low infection prevalences may be typical of natural foci of infection where deer could be a major host of ticks and E. phagocytophila.

Animals↗
PubMed1998

Cloning of the Arabidopsis ent-kaurene oxidase gene GA3.

The ga3 mutant of Arabidopsis is a gibberellin-responsive dwarf. We present data showing that the ga3-1 mutant is deficient in ent-kaurene oxidase activity, the first cytochrome P450-mediated step in the gibberellin biosynthetic pathway. By using a combination of conventional map-based cloning and random sequencing we identified a putative cytochrome P450 gene mapping to the same location as GA3. Relative to the progenitor line, two ga3 mutant alleles contained single base changes generating in-frame stop codons in the predicted amino acid sequence of the P450. A genomic clone spanning the P450 locus complemented the ga3-2 mutant. The deduced GA3 protein defines an additional class of cytochrome P450 enzymes. The GA3 gene was expressed in all tissues examined, RNA abundance being highest in inflorescence tissue.

Amino Acid Sequence↗