PubMed Health⌕ Search

Biomedical subjects

G N Brown

Publications and source records attributed to G N Brown.

At least 19 recordsLinked to original sources
PubMed1997

Anticipatory breeding for resistance to rust diseases in wheat.

Anticipatory resistance breeding is the process of predicting future pathotypes and producing resistant germplasm to avert future losses. It is made possible by a national pathotype surveillance program and knowledge that new pathotypes arise predominantly from mutation in existing pathotypes. This is supported by genetic analyses to catalogue the identity and distribution of resistance genes in current cultivars. A national germplasm enhancement program ensuring that both currently effective and potentially new sources of resistance are available in a wide range of adapted genotypes enables rapid cultivar replacement before or soon after the occurrence of new pathotypes. The policy of recommending only rust-resistant cultivars in the more rust-prone areas has resulted in significant reductions in pathogen population size and variability. With increased and more rapid international human travel and transport, there is an increased threat of exotic pathotypes, the effects of which are more difficult to predict. As the frequency and magnitude of epidemics decline, public awareness programs will be required to achieve and maintain the use of rust resistance by the entire wheat industry.

Journal Article↗
PubMed1994

Growth of wool follicles in culture.

A procedure for the culture of isolated wool follicles from Merino sheep is described. Follicles were microdissected from midside skin samples of 2-yr-old wethers and transferred, individually, to 24-well tissue culture plates. When maintained in supplemented Williams' E medium containing 5 to 10% fetal bovine serum (FBS), insulin, hydrocortisone, and a trace element mixture, fibre growth rates of 40 to 80 microns/day were observed. Follicles maintained their morphologic integrity for up to 7 days, incorporated [methyl-3H]thymidine into DNA and [35S]methionine into intermediate-filament keratins of the growing fiber. Insulin and hydrocortisone stimulated fiber growth at concentrations of 10 micrograms/ml and 50 ng/ml, respectively, but higher doses were inhibitory. The growth of fibers in response to hydrocortisone and the changes in follicle morphology was similar to those induced in skin after systemic administration of cortisol in vivo. A positive interaction between hydrocortisone and trace elements for follicle survival and hydrocortisone, insulin, and FBS for fiber growth was also found. The successful culture of Merino sheep follicles provides a model with which to study the direct influence of endocrine, nutritional and local factors on wool keratin synthesis independently of systemic shifts in the animals' metabolism.

Aging↗
PubMed1982

Structural Changes in Thylakoid Proteins during Cold Acclimation and Freezing of Winter Rye (Secale cereale L. cv. Puma).

Thylakoids were isolated from nonhardened and cold-hardened winter rye (Secale cereale L. cv. Puma), and subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis in the presence and absence of sulfhydryl reagents. Electrophoresis of cold-hardened rye thylakoid proteins revealed the presence of a 35 kilodalton polypeptide and the absence of a 51 kilodalton polypeptide found in nonhardened rye thylakoid proteins. The 35 kilodalton band could be induced by adding beta-mercaptoethanol to nonhardened rye thylakoid proteins, whereas the 51 kilodalton band could be formed by adding cupric phenanthroline to these same proteins. Sulfhydryl group titration showed that cold-hardened rye thylakoid proteins contained more free sulfhydryls than nonhardened rye proteins. Although amino acid analysis of thylakoid proteins revealed quantitative differences in several amino acid residues, the polarity of thylakoid proteins did not change during cold acclimation. No significant changes in sodium dodecyl sulfate-polyacrylamide gels of thylakoid proteins appeared when either nonhardened or cold-hardened plants were frozen in vivo or in vitro. However, thylakoid proteins did aggregate when frozen in the presence of beta-mercaptoethanol. Although thylakoid proteins isolated from cold-hardened rye contained more reduced thiols, a general state of reduction did not act as a cryoprotectant. It is hypothesized that conformational changes of specific proteins may be important for low temperature growth of rye.

Journal Article↗
PubMed1977

Effects of chill stress on prompt and delayed chlorophyll fluorescence from leaves.

This paper describes the utilization of a portable solid state device for the simultaneous measurement of prompt and delayed fluorescence transients in leaves from a variety of species subjected to temperature lowering. The induction transients of the two phenomena were not identical as the peak in prompt fluorescence yield always preceded that of delayed fluorescence. Temperature lowering delayed the occurrence of peak fluorescence, increased prompt fluorescence yield, decreased delayed fluorescence yield, and caused the occurrence of a new, more rapid delayed fluorescence transient. Leaves from all species had qualitatively the same type of induction curves although the response to temperature differed between species. The delayed fluorescence yield of chill-sensitive species was reduced to a greater extent than that of chill-insensitive species. Cold hardening leaf material did not greatly change the fluorescence response to temperature lowering. Arrhenius plots showed a linear relationship between delayed fluorescence yield and temperature. There were no breaks that would suggest membrane lipid phase changes. The data indicate that thylakoid membranes of chill-sensitive species are less capable of maintaining a light-induced high energy state at low temperatures than are thylakoid membranes of chill-resistant species.

Journal Article↗
PubMed1975

Ribosomal Changes during Induction of Cold Hardiness in Black Locust Seedlings.

Protein synthesis has been implicated in the cold-hardening process. Ribosomes from cold hardy and nonhardy black locust (Robinia pseudoacacia L.) seedlings were compared to determine if cold acclimation is related to alteration of ribosomal structure. Ribosomal structure, as indicated by thermal melting profiles, appears to be altered during induction of hardiness. Two-dimensional polyacrylamide gel electrophoresis of ribosomal proteins indicates at least 17 proteins from hardy seedlings that are different from those of nonhardy seedlings. These different proteins may be partially responsible for the different thermal melting profiles observed.

Journal Article↗
PubMed1974

Isoaccepting Transfer Ribonucleic Acids during Chilling Stress in Soybean Seedling Hypocotyls.

Total aminoacylation of glycine and leucine transfer RNAs was compared between chilled and nonchilled hypocotyls of 7-day-old soybean seedlings. Total charging was greater for both specific transfer RNAs from nonchilled sources. Isoaccepting transfer RNA species for glycine and leucine were fractionated using reverse phase column chromatography. Leucyltransfer RNAs were fractionated into six distinct fractions with relatively small shifts appearing in specific fractions between chilled and nonchilled sources. Glycyl-transfer RNAs were fractionated into two distinct fractions with major shifts appearing for both fractions between chilled and nonchilled sources.

Journal Article↗
PubMed1974

l-Phenylalanine Ammonia-lyase Activity in Robinia pseudoacacia Seedlings: I. Cyclic Phenomenon Activity during Continuous Light.

Influences of light and darkness on l-phenylalanine ammonia-lyase activity of black locust (Robinia pseudoacacia) seedlings were studied. Light initiates both an increase in enzyme activity (or enzyme synthesis) and a subsequent decrease in activity. These dual influences of light create cyclic changes in l-phenylalanine ammonia lyase activity in continuous light. The cyclic changes in activity (during continued light) cannot be attributed to an endogenous rhythm and rather are related to the changes in balance between the enzyme activity and its inactivating system.

Journal Article↗
PubMed1969

Changes in Nucleic Acid Fractions of Seed Components of Red Pine (Pinus resinosa Ait.) during Germination.

Changes in nucleic acid fractions of Pinus resinosa during seed germination were studied. At various stages of seed germination, embryos and megagametophytes were surgically separated and nucleic acids were extracted separately by a phenol-method. Total nucleic acids were fractionated on single-layer methylated albumin kieselguhr (MAK) columns. Total nucleic acids in embryos increased significantly 2 days after seeds were moistened, whereas, in megagametophytes, total nucleic acids stayed almost at a constant level until they degenerated at the time of shedding. In embryos, ribosomal RNAs (rRNA) increased 2 days after seeds were sown, whereas soluble RNA (sRNA) increased at 3 days. By comparison, nucleic acid fractions of megagametophytes did not show any quantitative changes during germination, except that rRNA fractions decreased shortly before shedding of seed coats. In dormant embryos the proportion of DNA was high and the proportions of sRNA and rRNA were low, whereas in megagametophytes at dormancy the proportions were completely reversed. As seed germination progressed, proportions of nucleic acid fractions in embryos changed significantly. In megagametophytes, although proportions of individual fractions remained almost constant throughout the experimental period, incorporation of (32)P into sRNA and rRNA of megagametophytes indicated turnover of these fractions.

Journal Article↗
PubMed1969

Changes in ribonucleic acid fractions during maturation of mimosa epicotyl tissues.

Total RNA and DNA of mimosa epicotyl tissues were extracted and the RNA fractionated into specific soluble RNAs (sRNAs) at different times during late germination. Epicotyls collected at each time contained qualitatively comparable meristematic and developing tissues, while mature tissues increased. Quantitative ratios of total RNA to DNA and total sRNAs to approximated ribosomal RNA (rRNA) varied consistently during development. Terminal nucleosides of sRNA did not vary in any consistent pattern through development. On the other hand, regular changes in quantitative ratios of specific sRNA groups were observed during development.

DNA↗