ABSTRACT
Bleaching herbicides belong to a chemically diverse group of inhibitors. This chapter introduces the bleaching herbicides together with their target enzyme and then reviews different approaches leading to genetically altered resistant organisms. The phytotoxic effect of bleaching herbicides is related to the function of the carotenoids in plants. These pigments are associated with membrane-bound chlorophyll-protein complexes of the photosynthetic apparatus. Genes of phytoene desaturase have been cloned and sequenced from several bacteria, the fungus Neurospora crassa, cyanobacteria, a green alga, and higher plant species such as soybean. Comparison of the amino acid sequence deduced from the phytoene desaturase genes revealed a remarkably high homology among the polypeptides from a green alga, a cyanobacterium, or a higher plant. Elevated resistance against norflurazon was observed in the transgenic tobacco plants during growth on media containing norflurazon, or on soil watered with a norflurazon solution. This resistance was confirmed to be dominantly inherited to the progeny.
