Actinonin is a naturally occurring hydroxamic acid and a potent inhibitor of the essential cotranslational protein processing enzyme peptide deformylase. Actinonin has both pre- and post-emergence herbicidal activity, but it is rapidly metabolized by plants, thus limiting herbicidal efficacy. Studies designed to elucidate the metabolic fate of actinonin revealed that after absorption actinonin was metabolized by tobacco plants with only about 17% of the parent compound remaining 48 h after application. Subcellular fractionation revealed that a microsomal fraction was capable of metabolizing actinonin in vitro. Two actinonin metabolites were isolated by reverse-phase high-performance liquid chromatography and identified by mass spectrometric analyses. The major metabolite was derived from the hydrolysis of the hydroxamate group to its corresponding acid, and a relatively minor metabolite through reduction of the hydroxamate group to the corresponding amide. Both metabolites were functionally inactive as inhibitors of peptide deformylase. These results provide rationale for the low efficacy of actinonin as a broad-spectrum herbicide, and identify functional groups in actinonin targeted by plants during detoxification. This information may facilitate the design and synthesis of actinonin analogues with increased herbicidal efficacy.

The effect of extensive feeding, confinement and diet supplementation with a-tocopheryl acetate (100 mg/kg) on the fatty acid composition and tocopherol concentration of microsome extracts and their susceptibility to oxidation was studied in Iberian pigs. The diet of pigs raised extensively was mostly composed of acorn and grass. The a-tocopherol contents of acorn and grass were 20 and 171 mg/kg dry matter, respectively. Microsomal fatty acid composition showed no differences among groups. Pigs feeding extensively had a higher concentration of a-tocopherol in muscle and microsomes than pigs given mixed diet with the basal level of a-tocopheryl acetate (P < 0·05) but lower values than pigs given supplementary levels (100 mg/kg) (P < 0·05). Microsomal fractions from pigs given mixed diet with a basal level of a-tocopheryl acetate were significantly more susceptible to iron-induced lipid oxidation than extract from pigs given diets containing a supplementary level (P < 0·05). Microsomal extracts from pigs feeding extensively had the lowest oxidation rate (P < 0·05), suggesting that other dietary constituents may play a role in the stabilization of microsomal lipids.

We compared the plasma membrane, tonoplast and mitochondrial Mg-ATPase activities of microsomes isolated from mycorrhizal and non-mycorrhizal sunflower (Helianthus annuus L.) and onion (Allium cepa L.) roots during a time-course experiment (21–60 d). No significant difference was observed between the protein levels of root microsomes from mycorrhizal and non-mycorrhizal sunflower. However, the protein content of microsomes obtained from mycorrhizal onion roots increased when the symbiosis was well established (more than 50% of root length colonized by the arbuscular mycorrhizal fungus). Kinetic studies revealed that vanadate-sensitive (plasma membrane-associated) ATPase activity of sunflower root microsomes increased with mycorrhizal colonization. However, the vanadate-sensitive ATPase activity of microsomes from mycorrhizal onion roots decreased compared with those from non-mycorrhizal controls. Increased activity of nitrate (tonoplast-associated) and azide (mitochondrial membrane-related)-sensitive ATPase activities was detected in extracts obtained from 45- and 60-d-old mycorrhizal onion plants. A slight increase in azide-sensitive ATPase activity was detected in microsomes of mycorrhizal sunflower. The existence of different physiological and biochemical strategies in sunflower and onion in relation to the establishment of this mutualistic symbiosis is discussed.