Chlorophyll Fluorescence of a Higher Plant as an Assay for Toxicity Assessment of Soil and Water

Abstract

The chlorophyll fluorescence (CF) assay is recognized as an important tool for monitoring the electron transport system of photosynthesis. The increase or decrease of fluorescence, compared to control, can indicate a lesion in the chain of events in photosynthesis or damage to the chloroplasts. Inhibition of photosynthesis in leaf segments of Tradescantia by herbicides (glyphosate, picloram & 2,4-D, triclopyr and hexazinone), heavy metals (Zn, Cu, Cd), a surfactant (sodium lauryl sulfate), and sodium fluoride (NaF) has been demonstrated using this method. The strongest changes of fluorescence induction curves were caused by hexazinone. Photosynthetic inhibition was observed as an increase in initial fluorescence (Fo) and a decrease in variable fluorescence (Fv) and electron pool size (EP). A CF assay predicted herbicidal injury in Tradescantia leaves at least 24 h before leaf necrosis appeared. Three heavy metals (Zn, Cu, Cd) are known as strong respiration and photosynthetic inhibitors in plant cells. In this study cadmium chloride, at the highest concentration (1000 ppm) tested, caused the strongest changes in Fv and EP size, which are characteristics of Photosystem II (PS II) photochemistry. Phytotoxicity of NaF caused an increase in Fv and EP compared to the control.

Using chlorophyll a fluorescence to detect the onset of anthracene photoinduced toxicity in Lemna gibba, and the mitigating effects of a commercial humic acid

“…F v /F m decreases in response to several stresses including photoinhibition and UV light (Streb et al 1993;Hofstraat et al 1994;Herrmann et al 1995), as well as chemical contaminants (Krupa et al 1993;Prevot et al 1993;Streb et al 1993;Sgardelis et al 1994;Gensemer et al 1996). The parameter t ½ represents the size and accessibility of the plastoquinone pool which accept electrons from PS2 (Judy et al 1990;Krause and Weis 1991;Sgardelis et al 1994). Contaminant stress diminishes this time from ϳ180-300 ms in healthy plants to Ͻ100 ms in severely affected individuals (Sgardelis et al 1994;Gensemer et al 1996).…”

“…0.8 in higher plants (Büchel and Wilhelm 1993). The parameter t ½ represents the time required to reach half of F v during the saturating light pulse and is a measure of the size and accessibility of the plastoquinone pool which accept electrons from PS2 (Judy et al 1990;Krause and Weis 1991;Sgardelis et al 1994). More specific details on parameter estimates are given by Gensemer et al (1996).…”

“…However, suborganismal endpoints (i.e., biomarkers or bioindicators) are now commonly used in aquatic toxicity testing and risk assessment (McCarthy and Shugart 1990;Benson and DiGiulio 1992;Huggett et al 1992). For plants, an important suborganismal process that can be inhibited by chemical contaminants is photosynthesis (Simpson et al 1988;Judy et al 1990;Lewis 1995). Many assays measure photosynthetic performance, of which some of the potentially most sensitive involve chlorophyll a (Chl a) fluores-cence induction kinetics (Hipkins and Baker 1986).…”

Impact of Foliar Diseases on Photosynthesis, Protein Content and Seed Yield of Alfalfa and Efficacy of Fungicide Application

“…Even low levels of infection dramatically reduced t 1/2 . Since t 1/2 is proportional to the size and accessibility of electron acceptors available to PSII (Judy et al, 1990), this finding suggests that highly localized infections may hamper the efficiency of PSII, even when the overall photochemical yield resembles that found in healthy leaves.…”

“…To minimize potential differences in leaf age on protein content, leaf samples were collected from the same position in the plant canopy for both infected and healthy leaves. Chlorophyll fluorescence has been used to measure the energetic state of photosynthesis in plants, especially in studies on environmental stresses such as extreme temperature, drought, or exposure to chemical agents (Judy et al, 1990(Judy et al, , 1991. Leaves were carefully selected to represent the lower end of each severity category.…”