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Articles

Effects of the Herbicide San 9789 on Photomorphogenic Responses ¹

^a Smithsonian Radiation Biology Laboratory, 12441 Parklawn Drive, Rockville, Maryland 20852

The herbicide, 4-chloro-5-(methylamino)-2-(,,-trifluoro-m-tolyl)- 3(2H)-pyridazinone (San 9789), an inhibitor that prevents both carotenoid and chlorophyll accumulation and normal chloroplast development in white light, does not affect the physiological effectiveness of phytochrome in dark-and light-grown plants. Red/far red reversibility of growth inhibition, stimulation of anthocyanin synthesis, and stimulation of phenylalanine ammonia-lyase synthesis are not significantly different in plants grown with and without San 9789. Despite the complete absence of photosynthesis, flowering could be induced in the long day plant Hordeum vulgare L. when sucrose was provided to the leaves. Since the nonphotochemical reactions of phytochrome also are not affected by the herbicide, San 9789 may be used as a tool to study the phytochrome system spectrophotometrically in plants grown for relatively long periods under high intensity white light.

¹ This work was partially supported by the Deutsche Forschungsgemeinschaft and carried out under partial support of the Department of Energy under Contract EY-76-S-05-4241. Part of the experimental work was done at the Institut fur Biologie II (SFB 46) in Freiburg, Germany.