title: A miniature bioassay for testing the acute phytotoxicity of photosystem II herbicides on seagrass.
abstract: Photosystem II (PSII) herbicides have been detected in nearshore tropical waters such as those of the Great Barrier Reef and may add to the pressure posed by runoff containing sediments and nutrients to threatened seagrass habitats. There is a growing number of studies into the potential effects of herbicides on seagrass, generally using large experimental setups with potted plants. Here we describe the successful development of an acute 12-well plate phytotoxicity assay for the PSII herbicide Diuron using isolated Halophila ovalis leaves. Fluorescence images demonstrated Diuron affected the entire leaf surface evenly and responses were not influenced by isolating leaves from the plant. The optimum exposure duration was 24 h, by which time the inhibition of effective quantum yield of PSII (∆F/F(m)') was highest and no deterioration of photosystems was evident in control leaves. The inhibition of ∆F/F(m)' by Diuron in isolated H. ovalis leaves was identical to both potted and hydroponically grown plants (with leaves remaining attached to rhizomes), indicating similar reductions in photosynthetic activity in these acute well-plate assays. The sensitivity of the assay was not influenced by irradiance (range tested 40 to 400 μmol photons m(-2) s(-1)). High irradiance, however, caused photo-oxidative stress in H. ovalis and this generally impacted in an additive or sub-additive way with Diuron to damage PSII. The bioassay using isolated leaves is more rapid, uses far less biological material and does not rely on specialised aquarium facilities in comparison with assays using potted plants. The development and validation of this sensitive bioassay will be useful to reliably screen and monitor the phytotoxicity of existing and emerging PSII herbicides and contribute to risk assessments and water quality guideline development in the future.
authors: College of Marine and Environmental Sciences, James Cook University, Townsville, Queensland, Australia; Australian Institute of Marine Science, Townsville, Queensland, Australia.
authors: Adam D
authors: AD
authors: Wilkinson
authors: College of Marine and Environmental Sciences, James Cook University, Townsville, Queensland, Australia; Centre for Tropical Water & Aquatic Ecosystem Research (TropWATER), James Cook University, Cairns, Queensland, Australia.
authors: Catherine J
authors: CJ
authors: Collier
authors: Australian Institute of Marine Science, Townsville, Queensland, Australia.
authors: Florita
authors: F
authors: Flores
authors: Australian Institute of Marine Science, Townsville, Queensland, Australia; School of Medicine, University of Queensland and National Research Centre for Environmental Toxicology, Coopers Plains, Queensland, Australia.
authors: Phil
authors: P
authors: Mercurio
authors: School of Medicine, University of Queensland and National Research Centre for Environmental Toxicology, Coopers Plains, Queensland, Australia.
authors: Jake
authors: J
authors: O'Brien
authors: Plant Functional Biology and Climate Change Cluster (C3), University of Technology, Sydney, New South Wales, Australia.
authors: Peter J
authors: PJ
authors: Ralph
authors: Australian Institute of Marine Science, Townsville, Queensland, Australia.
authors: Andrew P
authors: AP
authors: Negri
mesh_terms: D001681:Biological Assay / Q000379:methods*; D004237:Diuron / Q000633:toxicity; D004305:Dose-Response Relationship, Drug; D006540:Herbicides / Q000633:toxicity*; D045332:Photosystem II Protein Complex / Q000037:antagonists & inhibitors*; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism; D006109:Poaceae / Q000187:drug effects* / Q000378:metabolism*; D012680:Sensitivity and Specificity; D023382:Toxicity Tests, Acute; D014874:Water Pollutants, Chemical / Q000633:toxicity
chemical_list: D006540:Herbicides; D045332:Photosystem II Protein Complex; D014874:Water Pollutants, Chemical; D004237:Diuron