A new inhibitor of carotenoid synthesis in higher plants: 4-Chloro-5-(dimethylamino)-2-α,α,α, (trifluoro-m-tolyl)-3(2H)-pyridazinone (Sandoz 6706)

Changes occurring in several chloroplast components during Norflurazon-induced photobleaching of Pisum sativum seedlings were investigated. mRNA steady state levels of the chlorophyll a/b-binding protein of photosystem II, ferredoxin I, the small and large subunits of ribulose 1,5-bisphosphate carboxylase, and pEA214 and pEA207, two other lightresponsive genes, were determined during chlorophyll photooxidation. Relative transcription rates were assayed in isolated nuclei. The results illustrate a complex set of interactions regulating expression of the nuclear and chloroplast genomes. Photobleaching was found to affect the expression of the various genes in different ways. While transcript levels of the chlorophyll a/b-binding protein decreased by more than 80% under photooxidative light conditions in carotenoid-deficient peas, levels of ferredoxin, the small and large subunits of ribulose 1,5-bisphosphate carboxylase, and pEA214 mRNAs were reduced by less than 50%. pEA207 mRNA levels, on the other hand, were resistant to the effects of photobleaching. Analyses of chlorophylls a and b and the chlorophyll al b-binding protein suggest that accumulation of the protein and its mRNA are coordinated with chlorophyll abundance at several steps. In addition to post-transcriptional regulation at the level of mRNA and protein stability, there may exist coordination at the transcriptional stage.Since most (>80%) chloroplast proteins are nuclear encoded (14), the nuclear and chloroplast genomes must coordinate gene expression to bring about normal development of a green plant. The messenger RNAs of the nuclear-encoded chloroplast proteins are translated on cystosolic ribosomes and transported into the plastid where they are incorporated into the photosynthetic machinery. The nuclear-chloroplast interaction can be studied both during greening ofetiolated tissue and by the use ofmutants lacking Chl. In addition, one can study plants that are blocked in carotenoid biosynthesis either because of mutations or due to growth in the presence of herbicides such as Norflurazon [NF4; 4-chloro-5-(methylamino)-2-(a,a,a-trifluoro-m-tolyl)-3(2H)-pyridazinone] (7). In the absence of protecting carotenoids in these plants, high light intensities cause "bleaching" of the green parts(1, 19).

mentioning

confidence: 99%

Light Effects on Several Chloroplast Components in Norflurazon-Treated Pea Seedlings

Sagar¹,

Horwitz²,

Elliott³

et al. 1988

“…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.…”

mentioning

confidence: 99%

Effects of the Herbicide San 9789 on Photomorphogenic Responses

Jabben¹,

Deitzer²

1979

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 results obtained in this study showed that San 6706 exerted its effect on carotenoid synthesis before any significant change in the Chl content was observed. In addition, Bartels and McCullough (4) showed that San 6706 had a very slight effect, if any, on the synthesis of a-tocopherol of wheat seedlings in the dark or in low light intensity, while at the same time the synthesis of the colored carotenoids were drastically inhibited.…”

Section: Discussionmentioning

confidence: 99%

Interference in Carotenogenesis as a Mechanism of Action of the Pyridazinone Herbicide Sandoz 6706

Ben-Aziz¹,

Koren²

1974

The herbicide Sandoz 6706 (4-chloro-5-(dimethylamino)-2-a a, a, (trifluoro-m-tolyl)-3(2H)-pyridazinone), when applied as a preplant soil treatment at a concentration of 0.05 ,ig/g reduced the content of ,B-carotene and chlorophylls in 21-dayold wheat seedlings (Triticum aestivuml L.) by 55% and 29%, respectively, without affecting the fresh or dry matter of the seedlings. At 0.8 ug/g, the herbicide reduced the content of A-carotene and chlorophyll by as much as 98%, while the fresh weight of the albino seedlings was reduced by only 24%.