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 Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via CrossRef Citing Articles via Web of Science (69) Citing Articles via Google Scholar Google Scholar Articles by Vaisberg, A. J. Articles by Schiff, J. A. Search for Related Content PubMed PubMed Citation Articles by Vaisberg, A. J. Articles by Schiff, J. A. Agricola Articles by Vaisberg, A. J. Articles by Schiff, J. A.

Articles

Events Surrounding the Early Development of Euglena Chloroplasts

7. Inhibition of Carotenoid Biosynthesis by the Herbicide SAN 9789 (4-Chloro-5-(methylamino)-2-(,,,-trifluoro-m-tolyl)-3-(2H)pyridazinone) and Its Developmental Consequences ¹

^a Institute for Photobiology of Cells and Organelles, Brandeis University, Waltham, Massachusetts

The herbicide SAN 9789 (4-chloro-5-(methylamino)-2-(,,-trifluoro-m-tolyl-3- (2H)pyridazinone) blocks carotenoid synthesis in growing and resting cells of Euglena at concentrations of 20 to 100 µg/ml without affecting cell viability. Although the inhibition is immediate and complete, in resting cells no decrease in already synthesized carotenoids is found indicating a lack of turnover. In cells growing in the dark, carotenoids are diluted out as the cells divide. Cells dividing in the light in the presence of SAN 9789, eventually lose viability, presumably because of photooxidations usually prevented by carotenoids. During 72 hours of light-induced plastid development in dark-grown resting cells, none of the usual carotenoids increase while phytoene accumulates, indicating that SAN 9789 blocks carotenoid synthesis at this point. Chlorophyll synthesis and membrane formation are also blocked by the herbicide, but these inhibitions appear to be secondary to the inhibition of carotenoid synthesis. That carotenoid levels are strongly correlated with and may control the synthesis of chlorophyll and the formation of plastid membranes is suggested by the following data. (a) If dark-grown dividing cells are placed in the presence of the herbicide for various periods, rested and exposed to light in the presence of the drug, different amounts of carotenoids remain in the cells and the amount of chlorophyll finally synthesized is proportional to the amount of carotenoids present. (b) Photodestruction of chlorophyll is excluded, since the same amounts of chlorophyll are formed at intensities of 10 to 100 foot-candles of light. (c) Photoconversion of protochlorophyll(ide) to chlorophyll(ide) in dark-grown cells is not blocked by the herbicide. (d) Initial rates of chlorophyll synthesis are the same in treated and nontreated cells. (e) The extent of membrane formation appears to parallel the amount of carotenoids present as judged by electron microscopy.

³ Abraham and Etta Goodman Professor of Biology; to whom reprint requests should be directed.

¹ Research was supported by Grant GM 14595 from the National Institutes of Health.

This article has been cited by other articles:

				B.-L. Lin and W.-J. Yang Blue Light and Abscisic Acid Independently Induce Heterophyllous Switch in Marsilea quadrifolia Plant Physiology, February 1, 1999; 119(2): 429 - 434. [Abstract] [Full Text]