Inhibition of a Photosystem II Electron Transfer Reaction by the Natural Product Sorgoleone

Effects of the alleochemical sorgoleone on photosynthetic electron transport by oxygen-evolving chloroplast thylakoids and Triton X-100-prepared Photosystem II (PSII) membranes were analyzed. The Hill activity of the thylakoids proved to be at least as sensitive to inhibition by sorgoleone as it was...

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Published in:Journal of agricultural and food chemistry 1997-04, Vol.45 (4), p.1415-1421
Main Authors: Gonzalez, Veronica Miranda, Kazimir, Janet, Nimbal, Chandrashekhar, Weston, Leslie A., Cheniae, G. M.
Format: Article
Language:English
Subjects:
Agronomy. Soil science and plant productions
Biochemistry
Biochemistry and biology
Biological and medical sciences
Chemical control
Chemical, physicochemical, biochemical and biological properties
Fundamental and applied biological sciences. Psychology
Parasitic plants. Weeds
Physics, chemistry, biochemistry and biology of agricultural and forest soils
Phytopathology. Animal pests. Plant and forest protection
Soil science
Weeds
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Summary:Effects of the alleochemical sorgoleone on photosynthetic electron transport by oxygen-evolving chloroplast thylakoids and Triton X-100-prepared Photosystem II (PSII) membranes were analyzed. The Hill activity of the thylakoids proved to be at least as sensitive to inhibition by sorgoleone as it was to DCMU [3-(3,4-dichlorophenyl)-1,1-dimethylurea], a potent herbicidal inhibitor of PSII. However, a Photosystem I (PSI) partial reaction was not affected by a 10-fold greater concentration of sorgoleone than is required for complete inhibition of Hill activity. Measurements of flash-induced chlorophyll a variable fluorescence showed that sorgoleone neither dissipated excitation energy nor diminished the amplitude of chlorophyll a variable fluorescence. However, it inhibited the decay of variable fluorescence as effectively as DCMU, which blocks the oxidation of the PSII-reduced primary electron acceptor, Q- A, by the PSII secondary electron acceptor, QB, by displacing QB from the D1 protein. Additionally, sorgoleone competitively inhibited the binding of [14C]atrazine to the QB locus. Increasing durations of trypsin proteolysis of the PSII membranes or thylakoids and of the QB-binding niche itself caused parallel losses of inhibition of O2 evolution from sorgoleone and DCMU, as well as from bromoxynil, a phenol-type herbicide also binding to the QB locus. Keywords: Allelopathy; sorgoleone; photosystem II; electron transfer; herbicide
ISSN:0021-8561
1520-5118
DOI:10.1021/jf960733w