This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by Allen, M. M. Articles by Steinback, K. E. Search for Related Content PubMed PubMed Citation Articles by Allen, M. M. Articles by Steinback, K. E. Agricola Articles by Allen, M. M. Articles by Steinback, K. E.

Articles

Effects of Photosystem II Herbicides on the Photosynthetic Membranes of the Cyanobacterium Aphanocapsa 6308 ¹

Department of Biological Sciences, Wellesley College, Wellesley, Massachusetts 02181

The effects of the photosystem II herbicides diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea) and atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) on the photosynthetic membranes of a cyanobacterium, Aphanocapsa 6308, were compared to the effects on a higher plant, Spinacia oleracea. The inhibition of photosystem II electron transport by these herbicides was investigated by measuring the photoreduction of the dye 2,6-dichlorophenol-indophenol spectrophotometrically using isolated membranes. The concentration of herbicide that caused 50% inhibition of electron transport (I₅₀ value) in Aphanocapsa membranes for diuron was 6.8 x 10^–9 molar and the I₅₀ value for atrazine was 8.8 x 10^–8 molar. ¹⁴C-labeled diuron and atrazine were used to investigate herbicide binding with calculated binding constants (K) being 8.2 x 10^–8 molar for atrazine and 1.7 x 10^–7 molar for diuron. Competitive binding studies carried out on Aphanocapsa membranes using radiolabeled [¹⁴C]atrazine and unlabeled diuron revealed that diuron competed with atrazine for the herbicide-binding site. Experiments involving the photoaffinity label [¹⁴C]azidoatrazine (2-azido-4-ethylamino-6-isopropylamino-2-triazine) and autoradiography of polyacrylamide gels indicated that the herbicide atrazine binds to a 32-kilodalton protein in Aphanocapsa 6308 cell extracts.

¹ This work was partially supported by National Science Foundation Grants PCM 8004529, SPI 7926912, and CDP 8002385, by a William and Flora Hewlett Foundation Grant of Research Corporation, by a Brachman-Hoffman grant from Wellesley College, and by Wellesley College.