A minooxyacetate was patented as a herbicide in 1964 .This compound is an in vitro inhibitor of phenylalanine ammonia-lyase,phenylalanine transaminase , other transaminases, and ethylene production in plants . In a major study, AOA was found to be a potent inhibitor of all plant transaminases tested.AOA inhibits alanine aminotransferase competitively with amino acid substrates and non-competitively with oxo-acid substrates. AOA acts as a pyridoxyl phosphate antagonist, and many plant transaminases are inhibited by such antagonists including, semicarbazide,hydroxylamine,and cyanide.In soybean seedlings,root-fed AOA has been shown to inhibit growth, and to reduce anthocyanin, activity is competitively inhibited by AOA with amino acid substrates and nonchlorophyll,and extractable PAL levels . Recently, an analog of AOA,N-t-butoxycarbonyl-AOA became available, but little or no information on the biological activity of this new compound has been published.
For several decades there has been considerable interest in using plant pathogens for biological weed control.Although a large number of pathogens have been discovered to infect various weeds, many of these pathogens have insufficient virulence to be useful in bioherbicide programs.If such interactions are sufficiently potent, lower concentrations of herbicides and pathogen propagules may be adequate to achieve weed control.Also plant defense may be intimately related to synergistic plant: pathogen interactions.Plant defense mechanisms are important to protect plant from attack by microorganisms, pathogens and other stress factors. Although some biochemical defenses in plants have been elucidated, nearly all of this information relates to crop plants. Only in a few instances has the biochemistry of pathogen interactions with weeds and the weed defense responses been investigated .Studies of AOA effects on certain pathogen: plant interactions have shown that this compound can lower plant defense and increase disease susceptibility inplants, i.e. , tobacco mosaic virus in tobacco , Fusarium oxysporum in tomato, and Puccinia coronata in oat.
These effects were generally attributed to the inhibition of PAL activity and/or concomitant reduction of phytoalexinsynthesis. However as previously stated, AOA has effects on many transaminases and other biochemical processes that might also be related to plant defense.Furthermore, AOA effects on weed pathogen interactions have not been studied,and there is little or no biological data on Boc-AOA.Higher plants and certain algae are the only eukaryotes that assimilate inorganic sulfur into organic compounds. Incorporation of inorganic sulfur intocysteine via cysteine synthaseis the final step in sulfate reduction/assimilation in plants as outlined. Cysteine is synthesized from serine in two steps; serine transferase catalyzesacetylation of serine using acetyl-CoA to yield O-acetylserine, and then CS catalyzes addition of inorganic sulfide to O-acetylserine with release of acetate and cysteine. CS has been deemed essential for plant growth and has been isolated from Datura and Brassica species and many other plants.The interactions of herbicides and safeners on CS as a potential target for new herbicidal compounds has also been examined.
CS has also been shown to be inhibited by AOA . Since CS requires pyridoxalphosphate as a cofactor, the enzyme is a possible sensitive site of AOA and Boc-AOA. Thus, it was also possible that these aminooxy-compounds might interact with these bioherbicides in a synergistic manner. Hemp sesbania and sicklepod seeds were harvested from weed plots grown at the Crop Production Systems Research Unit, Stoneville, MS. Seeds were mechanically scarified, planted in paper towel cylinders, and grown hydroponically in the dark as described previously . After 96 h growth, uniform seedlings were selected for test, and again placed in paper towel cylinders.Then seedlings were used in hydroponic bioassays, after treatment with chemicals, pathogen spores, or the combination of chemical and spores. C. truncatum infection in hemp sesbania also lowered CS activity,but A cassiae infection in sicklepod increased activity 20% above untreated control levels. In vitro enzyme assays resulted in equal inhibition by 15% when either chemical and the substrates were added simultaneously to the enzyme.When either inhibitor was pre-incubated with enzyme without substrate, and then followed by substrate addition and assay, inhibition by Boc-AOA was not increased to any measurable extent, whereas the inhibition by AOA increased by an additional 20%.Overall results indicate that hemp sesbania was generally more resistant than sicklepod to the phytotoxicity of AOA and Boc-AOA under these continuous dark-growth conditions and the greening of excised cotyledon test. The fact that these compounds had little effect after foliar application may be due to the waxy characteristics of these seedlings that could have slowed absorption of the compounds into the cytoplasm.