Effects of the Herbicide San 9789 on Photomorphogenic Responses

Abstract

The herbicide, 4-chloro-5-(methybano)-2-(aaa-trifluoro-m-tolyl)- In many plant species sublethal doses of 4-chloro-5-(methylamino)-2-(a,a,a-trifluoro-m-tolyl)-3(2H)-pyridazinone (Norflurazon; hereafter referred to as San 9789, manufacturer's code no.) inhibit carotenoid synthesis (2). When exposed to white light these plants do not accumulate Chl pigments, but appear to grow and develop as well as untreated plants for several days.Our interest in this herbicide evolved from the possibility of using it as a tool to study phytochrome spectrophotometrically in light-grown plants. Normally ChM fluorescence makes spectrophotometric measurements in light-grown plants impossible (18). Furthermore, R3/FR-reversible-fluorescence yield changes, unrelated to phytochrome, produce apparent A changes which could be confused with phytochrome (6

The Fate of Chloroplast Proteins during Photooxidation in Carotenoid-Deficient Maize Leaves

“…The most dramatic effect is that Chl fails to accumulate due to rapid photooxidation, resulting in albino seedlings which are incapable of photoautotrophic growth (1,6). Herbicides which block the accumulation of colored carotenoids exhibit phenotypes very similar to those of the nuclear albino mutants (23). Leaf plastids within these carotenoid-deficient seedlings show little or no development of internal membrane structure (4,14).…”

Photosynthetic sucrose acts as cotyledon-derived long-distance signal to control root growth during early seedling development in Arabidopsis

“…4A could be converted to long-root morphotypes by supplementary sucrose. To further test the hypothesis, we used three physiological treatments for inhibiting various sections of the photosynthetic apparatus in WT seedlings: (i) removal of CO 2 from the atmosphere in the light, (ii) preventing greening with the carotenoid-biosynthesis inhibitor norflurazone in the light (20), and (iii) preventing greening, but not PhyA-mediated photomorphogenesis, by growing the seedlings in far-red light (Fig. 5).…”

Anthocyanin Production in Chl-Rich and Chl-Poor Seedlings

“…The differences in anthocyanin production be- (1,4,5). However, these inhibitors should not be used in physiological experiments without previous studies of their effects on the response/system combination: differences in the effects of the inhibitor can be quite large even for the same response in closely related systems, as shown in this report.…”

“…Streptomycin inhibits chloroplast development and Chl synthesis and enhances anthocyanin production in young cabbage seedlings (9). We used STM instead of Norflurazon, a more commonly used 'Chl-bleacher' (1,4,5), because the differences in the Chl levels of seedlings exposed to prolonged irradiations with different spectral regions are less pronounced in STM-treated than in Norflurazon-treated seedlings (7). Figure 1 are the means of 14 to 18 replicates in two independent experiments.…”

“…Large amounts of Chl are formed during the prolonged irradiations required to elicit maximum anthocyanin production (9,10). As a consequence of light attenuation due to screening by Chl, the photoconversion and cycling rates and the photoequilibrium ratios of phytochrome in vivo are different from those predicted on the basis of the spectral parameters of purified phytochrome and may cause distortions in the action spectra of photomorphogenesis (6) of seedlings have been used in photomorphogenesis research to decrease the effects of Chl screening on the state of phytochrome and to allow spectrophotometric assays of phytochrome in vivo in light-grown seedlings (1,4,5). We also wanted to check if a specific inhibitor action on the photoresponse studied might affect the interpretation of the results in terms of the expected differences between the states of phytochrome in Chl-rich and Chl-poor seedlings (6).…”