Bleaching Herbicide Flurtamone Interferes with Phytoene Desaturase

Abstract

The mode of action of the furanone herbicide flurtamone and derivatives was investigated with cress seedlings and with the unicellular cyanobacterium Anacystis. Either in the light or in the dark these compounds inhibited the formation of a-and ,-carotene and all of the xanthophylls in the seedlings. Instead, phytoene, a precursor of colored carotenoids, was accumulated. In illuminated seedlings photooxidative destruction of chlorophyll was observed. The Iso value of flurtamone inhibition of carotenoid biosynthesis in intact Anacystis cells and the K, value for interaction of flurtamone with phytoene desaturase with Anacystis thylakoids were 30 and 18 nanomoles, respectively. Concentrations of flurtamone which strongly inhibited carotenoid synthesis had no direct peroxidative activities and did not inhibit photosynthetic electron transport.In recent years, several chemically unrelated bleaching herbicides have been developed (see Sandmann and Boger [1 1] for review). Their mode of action is inhibition of carotenoid biosynthesis. They decrease the level of colored carotenoids so that phytoene is accumulated instead. A subsequent photooxidative destruction of Chl is the consequence which may lead to complete bleaching of the pigments in the photosynthetic apparatus. For difunon (1), a diflufenican analog (9), and for norflurazon (6, 12) it could be demonstrated by in vitro studies that these herbicides directly interact with phytoene desaturase, the first enzyme in a series of carotene interconversion reactions leading to a-and (3-carotene.Flurtamone, a new furanone herbicide, has been introduced (14). As a preemergence herbicide it exhibits activity against a wide range of weeds and shows selectivity to several crops (7). As treated plants show all symptoms typical for a bleaching herbicide, we investigated the effect of flurtamone on the carotenoid content of cress seedlings as well as on the carotenoid pattern of Anacystis. Furthermore, membranes from this cyanobacterium were used to study the direct interaction of flurtamone with carotenogenic enzymes as previously demonstrated for other bleaching herbicides (5). MATERIALS AND METHODS CultivationCress seedlings (Lepidium sativum) were germinated and grown for 3 d on filter paper in Petri dishes with 4 mL tap water containing various flurtamone concentrations either in darkness or in light with 60 AE/m2 x s. The leaves were cut off, freeze dried, and extracted for carotenoids. Anacystis R2 (Synechococcus PCC 7942) was cultivated for 2 d as previously described (12). Cells were harvested by centrifugation and immediately used for carotenoid analysis or in vitro assays. Packed cell volume of the cultures was determined in graduated microcentrifuge tubes. The carotene-deficient mutant Phycomyces blakesleeanus C5 was grown for 4 d as previously described (13). Carotenoid AnalysisCarotenoids were extracted from Anacystis cells or pulverized cress leaves by hot extraction with methanol containing 6% KOH (20 min, 65°C). The filtered extracts were partitioned i...

A single polypeptide catalyzing the conversion of phytoene to zeta-carotene is transcriptionally regulated during tomato fruit ripening.

“…This activity was blocked by the herbicide flurtamone [5-methylamino-2-phenyl4-(3-trifluoromethylphenyl)-3(2H)furasone], which is a specific inhibitor of PDS (20 (Fig. 4).…”

Diphenylpyridines

“…Therefore less 6-carotene, the end product of this in vitro biosynthetic chain, is formed. Interaction of diphenylpyridines with phytoene desaturase is very similar to inhibition of this enzyme by flutamone (7). For the latter herbicide, it has shown that it is a reversible non-competitive inhibitor of phytoene desaturase.…”

Synthesis and herbicidal activities of novel 4-(3-trifluoromethylphenyl)-2H-pyridazin-3-one derivatives

“…Since phytoene desaturase (PDS) catalyzes dehydrogenation of phytoene to zeta carotene which protects chlorophyll from photo oxidation [1][2][3][4], it has been a well-known major target enzyme of herbicides in the cartenoid biosynthesis pathway and has attracted considerable attention. Up to now, many novel compounds (e.g., 2,6-diphenylpyridines [5,6], phenoxypyridincarbonamides [7,8], diarylpyrimidines [9,10], 1,1'-biphenyl derivatives [11], tetrahydropyrimidinones [12,13], phenylpyrimidinones [14], and diphenylpyrrolidinones [15]) have been identified as phytoene desaturase inhibitors and commercialized.…”