title: The Fungicide Phosphonate Disrupts the Phosphate-Starvation Response in Brassica nigra Seedlings.
abstract: The development of Brassica nigra seedlings over 20 d of growth was disrupted by the fungicide phosphonate (Phi) in a manner inversely correlated with nutritional inorganic phosphate (Pi) levels. The growth of Pi-sufficient (1.25 mM Pi) seedlings was suppressed when 10, but not 5, mM Phi was added to the nutrient medium. In contrast, the fresh weights and root:shoot ratios of Pi-limited (0.15 mM) seedlings were significantly reduced at 1.5 mM Phi, and they progressively declined to about 40% of control values as medium Phi concentration was increased to 10 mM. Intracellular Pi levels generally decreased in Phi-treated seedlings, and Phi accumulated in leaves and roots to levels up to 6- and 16-fold that of Pi in Pi-sufficient and Pi-limited plants, respectively. Extractable activities of the Pi-starvation-inducible enzymes phosphoenolpyruvate phosphatase and inorganic pyrophosphate-dependent phosphofructokinase were unaltered in Pi-sufficient seedlings grown on 5 or 10 mM Phi. However, when Pi-limited seedlings were grown on 1.5 to 10 mM Phi (a) the induction of phosphoenolpyruvate phosphatase and inorganic pyrophosphate-dependent phosphofructokinase activities by Pi limitation was reduced by 40 to 90%, whereas (b) soluble protein concentrations and the activities of the ATP-dependent phosphofructokinase and pyruvate kinase were unaffacted. It is concluded that Phi specifically interrupts processes involved in regulation of the Pi-starvation response in B. nigra.
authors.affiliation: Departments of Biology and Biochemisty, Queens University, Kingston, Ontario, Canada K7L 3N6 (C.C., M.E.T., W.C.P.).
authors.forename: C.
authors.initials: C
authors.lastname: Carswell
authors.forename: B. R.
authors.initials: BR
authors.lastname: Grant
authors.forename: M. E.
authors.initials: ME
authors.lastname: Theodorou
authors.forename: J.
authors.initials: J
authors.lastname: Harris
authors.forename: J. O.
authors.initials: JO
authors.lastname: Niere
authors.forename: W. C.
authors.initials: WC
authors.lastname: Plaxton