Inhibition of photosystem II (PSII) electron transport as a convenient endpoint to assess stress of the herbicide linuron on freshwater plants
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Effects of the herbicide linuron on photosynthesis of the freshwater macrophytes Elodea nuttallii (Planchon) St. John, Myriophyllum spicatum L., Potamogeton crispus L., Ranunculus circinatus Sibth., Ceratophyllum demersum L. and Chara globularis (Thuill.), and of the alga Scenedesmus acutus Meyen, were assessed by measuring the efficiency of photosystem II electron flow using chlorophyll fluorescence.
In a series of single-species laboratory tests several plant species were exposed to linuron at concentrations ranging from 0 to 1000 μg l−1. It was found that the primary effect of linuron, inhibition of photosystem II electron flow, occurred with a half-lifetime of about 0.1 to 1.9 h after addition of linuron to the growth medium. The direct effect of the herbicide on photosynthesis appeared to be reversible. Complete recovery from the inhibition occurred with a half-lifetime of 0.5 to 1.8 h after transfer of linuron treated plants to linuron free medium. The EC50,24h of the inhibition of photosystem II electron transport by linuron was about 9–13 μg l−1 for most of the macrophytes tested. For S. acutus the EC50,72h for inhibition of photosystem II electron flow was about 17 μg l−1 for the free suspension, and 22 μg l−1 for cells encapsulated in alginate beads.
In a long-term indoor microcosm experiment, the photosystem II electron flow of the macrophytes E. nuttallii, C. demersum and the alga Spirogyra sp. was determined during 4 weeks of chronic exposure to linuron. The EC50,4weeks for the long-term exposure was 8.3, 8.7 and 25.1 μg l−1 for E. nuttallii, C. demersum and Spirogyra, respectively. These results are very similar to those calculated for the acute effects. The relative biomass increase of E. nuttallii in the microcosms was determined during 3 weeks of chronic exposure and was related to the efficiency of photosystem II electron transport as assessed in the different treatments.
It is concluded that effects of the photosynthesis inhibiting herbicide on aquatic macrophytes, algae and algae encapsulated in alginate beads can be conveniently evaluated by measuring photosystem II electron transport by means of chlorophyll fluorescence. This method can be used as a rapid and non-destructive technique in aquatic ecological research.
- Inhibition of photosystem II (PSII) electron transport as a convenient endpoint to assess stress of the herbicide linuron on freshwater plants
Volume 32, Issue 2 , pp 113-123
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- Kluwer Academic Publishers
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- chlorophyll fluorescence
- phenylurea herbicide
- photosynthetic electron flow
- single species test
- Author Affiliations
- 1. Department of Biomolecular Sciences, Laboratory for Plant Physiology, Wageningen Agricultural University, Arboretumlaan 4, NL-6703 BD, Wageningen, The Netherlands
- 2. Department of Water Quality Management and Aquatic Ecology, Wageningen Agricultural University, Ritzema bosweg 32a, NL-6703 AZ, Wageningen, The Netherlands
- 3. Winand Staring Centre for Integrated Land, Soil and Water Research, DLO, P.O. Box 125, NL-6700 AC, Wageningen, The Netherlands