title: A chlorophyll a fluorescence-based Lemna minor bioassay to monitor microbial degradation of nanomolar to micromolar concentrations of linuron.
abstract: A plant-microbial bioassay, based on the aquatic macrophyte Lemna minor L. (duckweed), was used to monitor biodegradation of nano- and micromolar concentrations of the phenylurea herbicide linuron. After 7 days of exposure to linuron, log-logistic-based dose-response analysis revealed significant growth inhibition on the total frond area of L. minor when linuron concentrations > or = 80 nM were added to the bioassay. A plant-protective effect was obtained for all concentrations > 80 nM by inoculation with either a bacterial consortium or Variovorax paradoxus WDL1, which is probably the main actor in this consortium. The outcome of the plant-microbe-toxicant interaction was also assessed using pulse amplitude-modulated chlorophyll a fluorescence and chlorophyll a fluorescence imaging. Linuron toxicity to L. minor became apparent as a significant decrease in the effective quantum yield (Delta F/Fm') within 90 min after exposure of the plants to linuron concentrations > or = 160 nM. Inoculation of the bioassay with the linuron-degrading bacteria neutralized the effect on the effective quantum yield at concentrations > or = 160 nM, indicating microbial degradation of these concentrations. The chlorophyll a fluorescence-based Lemna bioassay described here offers a sensitive, fast and cost-effective approach to study the potential of biodegrading microorganisms to break down minute concentrations of photosynthesis-inhibiting xenobiotics.
authors.affiliation: Laboratory of Phytopathology, Department of Crop Protection, Faculty of Agricultural and Applied Biological Sciences, Ghent University, Coupure Links 653, B-9000 Gent, Belgium.
authors.forename: Kris
authors.initials: K
authors.lastname: Hulsen
authors.forename: Veerle
authors.initials: V
authors.lastname: Minne
authors.forename: Peter
authors.initials: P
authors.lastname: Lootens
authors.forename: Paul
authors.initials: P
authors.lastname: Vandecasteele
authors.forename: Monica
authors.initials: M
authors.lastname: Höfte
mesh_terms: D029064:Araceae / Q000187:drug effects / Q000254:growth & development*; D001419:Bacteria / Q000378:metabolism*; D020562:Betaproteobacteria / Q000378:metabolism*; D001673:Biodegradation, Environmental; D001681:Biological Assay; D002734:Chlorophyll / Q000378:metabolism*; D000077194:Chlorophyll A; D004305:Dose-Response Relationship, Drug; D005470:Fluorometry; D006540:Herbicides / Q000378:metabolism*; D008044:Linuron / Q000378:metabolism*; D010860:Pigments, Biological / Q000378:metabolism
chemical_list: D006540:Herbicides; D010860:Pigments, Biological; D008044:Linuron; D002734:Chlorophyll; D000077194:Chlorophyll A