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Biomedical subjects

J. D. Walton

Publications and source records attributed to J. D. Walton.

4 recordsLinked to original sources
PubMed1997

Histone Hyperacetylation in Maize in Response to Treatment with HC-Toxin or Infection by the Filamentous Fungus Cochliobolus carbonum.

HC-toxin, the host-selective toxin produced by the filamentous fungus Cochliobolus carbonum, inhibits maize (Zea mays L.) histone deacetylases (HDs) in vitro. Here we show that HDs are also inhibited by HC-toxin in vivo, as demonstrated by the accumulation of hyperacetylated forms of the core (nucleosomal) histones H3.1, H3.2, H3.3, and H4 in both maize embryos and tissue cultures. Hyperacetylation of H4 and all isoforms of H3 in tissue cultures of inbred Pr (genotype hm/hm) occurred at 10 ng/mL (23 nM). The effect was host-selective; acetylation of histones in the near isogenic inbred Pr1 (genotype Hm/Hm) did not occur in tissue cultures or embryos treated with 0.2 [mu]g/mL or 10 [mu]g/mL HC-toxin, respectively. Hyperacetylation of histone H4 in embryos of Pr1 began to occur at 50 [mu]g/mL. HC-toxin, and 200 [mu]g/mL HC-toxin caused equal hyperacetylation in Pr and Pr1 embryos. Hyperacetylated core histones, especially of the isoforms of histone H3, accumulated in leaves of inbred Pr, but not Pr1, after infection by toxin-producing strains of C. carbonum. Accumulation of hyperacetylated histones began at 24 h after inoculation, before the development of visible disease symptoms. Hyperacetylation of H2A or H2B histones were not detected in any of the studies. The results are consistent with HD being a primary site of action of HC-toxin.

Journal Article↗
PubMed1993

Density Gradient Study of Victorin-Binding Proteins in Oat (Avena sativa) Cells.

Victorin-binding proteins (VBPs) in oat (Avena sativa) cells were identified using native victorin and anti-victorin polyclonal antibodies. Homogenates of oat tissues were fractionated in continuous or discontinuous sucrose density gradients or with an aqueous two-phase method, and covalent binding sites of victorin were detected by western blotting. In a 20 to 45% (w/w) sucrose continuous density gradient, the 100-kD VBP was located in fractions of 37 to 44% sucrose, with a peak at 39% sucrose. Based on marker enzyme assays, plasma membranes peaked at 39 to 41% sucrose, mitochondria peaked at 41%, but Golgi and endoplasmic reticulum were in lower density fractions, peaking at 28 to 29% and 22 to 24% sucrose, respectively. The 100-kD VBP was not found in plasma membranes purified by the aqueous two-phase method or in mitochondria purified by discontinuous density gradient centrifugation. Victorin binding to 65- and 45-kD proteins was detected in all fractions in the continuous sucrose density gradients. The 65- and 45-kD proteins were both detected in purified plasma membranes, but only the 65-kD protein was detected in purified mitochondria. The subcellular location of VBPs was the same in sensitive and resistant oat cells.

Journal Article↗
PubMed1992

A Biochemical Phenotype for a Disease Resistance Gene of Maize.

In maize, major resistance to the pathogenic fungus Cochliobolus (Helminthosporium) carbonum race 1 is determined by the dominant allele of the nuclear locus hm. The interaction between C. carbonum race 1 and maize is mediated by a pathogen-produced, low molecular weight compound called HC-toxin. We recently described an enzyme from maize, called HC-toxin reductase, that inactivates HC-toxin by pyridine nucleotide-dependent reduction of an essential carbonyl group. We now report that this enzyme activity is detectable only in extracts of maize that are resistant to C. carbonum race 1 (genotype Hm/Hm or Hm/hm). In several genetic analyses, in vitro HC-toxin reductase activity was without exception associated with resistance to C. carbonum race 1. The results indicate that detoxification of HC-toxin is the biochemical basis of Hm-specific resistance of maize to infection by C. carbonum race 1.

Journal Article↗