01893naa a2200145 a 450000100080000000500110000800800410001910000210006024500540008126000090013552015060014465000130165065000100166377300740167318365652012-09-05       1985    bl ---       0--  u    #d1 aWILKINSON, R. E.  aCarotenogenic inhibition by Norflurazon in wheat.  c1985  aWheat (Triticum aestivum L. cv Holley) seedlings were exposed to [N-14CH3]norflurazonin nutrient solution studies. The 14CH3 group was incorporated into a compound eluting on GLC at a relative retention temperature Rf equivalent to n-C21 H36 and mass spectrometry validated a 295 MW. The concentration of [N-14CH3]norflurazon and/or Rl[14C]norflurazon which resulted in carotenogenesis inhibition was 0.07 ?Min the water contained in the leaves. The concentration of norflurazon required for phytoene accumulation as a mode-of-action was ca. 140 × the concentration of norflurazon required for geranylgeraniol accumulation. Geranylgeraniol accumulated at 1 ppbw (3.2 nM) norflurazon and phytofluene accumulated throughout the norflurazon concentration series (1 to 1000 ppbw). Carotene content was increased by 1 to 16 ppbw norflurazon but was decreased by 64 ppbw norflurazon. Thus, two modes-of-activity for norflurazon are documented that depend upon concentration of the toxicant in the tissue. Norflurazon demethylation in prephytoenepyrophosphate synthesis resulted in a C21 conjugate and increased concentrations of GGPP and phytoene in the tissue. At approximately 31 ppbw norflurazon, an inhibition of phytoene dehydrogenation occurred and phytoene accumulated. At 62 ppbw norflurazon, phytofluene hydrogenation inhibition occurred and phytofluene accumulated while ?-carotene synthesis was inhibited. These inhibitions may possibly be reversible when substrate concentrations are in excess.  aCaroteno  aTrigo  tPesticide Biochemistry and Physiologygv. 23, n. 3, p. 370-377, 1985.