Phytoene Desaturase, the Essential Target for Bleaching Herbicides

Abstract

Many bleaching herbicides with different core structures inhibit phytoene desaturase (PD), a membrane-bound enzyme in the carotenogenic pathway catalyzing the hydrogen abstraction step at the first C40precursor of β-carotene. Prospects are good that new PD-active herbicides will be discovered by screening for bleaching activity. Accordingly, interest in PD enzymology and molecular genetics has increased. Although active carotenogenic cell-free systems are available, no isolation of PD has been achieved since the enzyme cannot be detected in its isolated form due to complete loss of activity. A portion of theRhodobacterPD gene was incorporated into an appropriate plasmid which could be expressed inE. coli.This system was used to produce an antibody specific against PD from higher plants as well asRhodobacter.All PDs assayed had an apparent molecular weight of 52 to 55 kDa. ARhodobactergene probe hybridized with a 3.1 kbBamH I fragment fromAphanocapsawhich allowed us to sequence the PD gene from this cyanobacterium. Its DNA sequence matched with the apparent molecular weight of the PD band in the western blot, and a fusion-gene product was found to be immunoreactive with theRhodobacterPD antibody,Anacystismutants were produced exhibiting cross-resistance against norflurazon and fluorochloridone. Apparently, this resistance is due to an altered PD with concurrent decrease of inhibitor binding affinity. Cloning of the resistant gene into the wild type is in progress.

Etioplast and etio-chloroplast formation under natural conditions: the dark side of chlorophyll biosynthesis in angiosperms

“…Pigment analyses performed on isolated photoactive dimers and large aggregates of LPOR-Pchlide-NADPH ternary complexes indicate the presence of carotenoids such as zeaxanthin and violaxanthin molecules (OuazzaniChahdi et al 1998). When etiolated plants were grown at room temperature, norflurazon, an inhibitor of phytoene desaturation (Sandmann and Böger 1997), did not cause aberrations in the ultrastructure of PLBs (Klockare et al 1981;Moro et al 2004); whereas amitrole, an inhibitor of lycopene cyclization (Agnolucci et al 1996), disrupted PLB formation (Di Baccio et al 2002;Moro et al 2004). However, at increased temperature, less ordered PLBs were observed in norfluorazon-treated leaves (Moro et al 2004), suggesting that polar carotenoids are required for plastid membrane stability (Havaux 1998).…”

Effects of Fluridone and Norflurazon on Conditioning and Germination of Striga asiatica Seeds

“…Fluridone [1-methyl-3-phenyl-5-(3-trifluoromethylphenyl)-4-(1H)-pyridinone], norflurazon [4-chloro-5-methylamino-2-(3-trifluoromethylphenyl)-3(2H)-pyridazinone], and diflufenican [N-(2,4-difluorophenyl)-2-(3-trifluoromethylphenoxy)-3-pyridinecarboxamide] are herbicides that block phytoene desaturase, which catalyzes the desaturation step of phytoene to phytofluene in the carotenoid biosynthesis pathway (Bartels and Watson 1978;Sandmann and Bo¨ger 1997). They also inhibit the biosynthesis of abscisic acid (ABA) in plants (Stewart and Voetberg 1987;Xu and Bewley 1995;Popova and Riddle 1996;Yoshioka et al 1998) because carotenoids are the main precursors of ABA in plants (Quatrana et al 1997).…”

Advances in selectable marker genes for plant transformation

“…Carotenoids are essential components of the photosynthetic apparatus. They participate in light harvesting and protect the chloroplast from the harmful effect of singlet oxygen formed during photosynthesis (Sandmann and Böger, 1997). PDSinhibiting herbicides prevent the formation of carotenoids, resulting in the degradation of chlorophyll and destruction of chloroplast membranes, which is characterized by the photobleaching of green tissues (Boger and Sandmann, 1998).…”