Purification and characterization of cactorein, a phytotoxin secreted by Phytophthora cactorum

Ian A. Dubery, Debra Meyer, Chris Bothma

Research output: Contribution to journalArticlepeer-review

10 Citations (Scopus)

Abstract

An extracellular, hydrophilic, thermostable and non-dialysable phytotoxin was purified to homogeneity from culture fluids of Phytophthora cactorum with a yield of 2.7 mg1-1. The toxin is an acidic protein with a Mr of 10 000 and a pI of 3.65. The amino acid composition was determined and resembles that of characterized members of the elicitin family of Phytophthora phytotoxins. Toxicity was evaluated with a cell viability assay using tobacco cell suspensions, and a LD50 value and a lethal dose of 38 and > 100 nM respectively, were determined for the purified toxin. When applied to tobacco plantlets, concentrations as low as 100 nM resulted in wilting and desiccation. Mature leaf tissue reacted hypersensitively to the toxin, with localized necrosis; and produced pathogenesis-related proteins in response to the toxin. The toxin induced rapid extracellular alkalinization in cultured tobacco cells and elicited active defence responses with concentration dependent induction of sesquiterpenoid phytoalexins. Rishitin, phytuberol and capsidiol accumulated in the medium to concentrations of 25, 14, and 63 nmol g-1 cells, 24 hr after exposure to a toxin concentration of 40 nM. Higher concentrations of toxin resulted in a loss of cell viability and eventual cell death.

Original languageEnglish
Pages (from-to)307-312
Number of pages6
JournalPhytochemistry
Volume35
Issue number2
DOIs
Publication statusPublished - Jan 1994

Keywords

  • Phytophthora cactorum
  • elicitin
  • oomycetes
  • pathogenesis related proteins.
  • phytoalexin
  • tobacco
  • toxin

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Plant Science
  • Horticulture

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