Inhibition of Plant Asparagine Synthetase by Monoterpene Cineoles

Abstract

Asparagine (Asn) synthetase (AS) is the key enzyme in Asn biosynthesis and plays an important role in nitrogen mobilization. Despite its important physiological function, little research has been done documenting inhibitors of plant AS. Plant growth inhibition caused by the natural monoterpene 1,4-cineole and its structurally related herbicide cinmethylin was reversed 65% and 55%, respectively, by providing 100 m Asn exogenously. Reversion of the phytotoxic effect was dependent on the concentration of Asn. The presence of either 1,4-cineole or cinmethylin stimulated root uptake of [ 14 C]Asn by lettuce (Lactuca sativa) seedlings. Although the physiological responses suggested that both compounds affected Asn biosynthesis, biochemical analysis of AS activity showed that the natural monoterpene was a potent inhibitor (I 50 ϭ approximately 0.5 m) of the enzyme, whereas the commercial product was not inhibitory up to levels of 10 mm. Analysis of the putative metabolite, 2-hydroxy-1,4-cineole, showed that the cis-enantiomer was much more active than the transenantiomer, suggesting that the hydroxyl group was involved in the specific ligand/active site interaction. This is the first report that AS is a suitable herbicide target site, and that cinmethylin is apparently a proherbicide that requires metabolic bioactivation via cleavage of the benzyl-ether side chain.

Efeitos potencialmente alelopáticos dos óleos essenciais de Piper hispidinervium C. DC. e Pogostemon heyneanus Benth sobre plantas daninhas

“…Adicionalmente a todas essas possibilidades de uso, os óleos essenciais revelam-se como potentes inibidores da germinação de sementes e do desenvolvimento de diferentes espécies de plantas, ação de bioerbicida (Kwak et al, 1999;Duke et al, 2000;Romagni et al, 2000;Duke et al, 2002).…”

Synthesis and Herbicidal Activities of the 0-Syn and 0-Anti Benzyl Epoxycyclopentyl Ethers

“…The cis relationship of the ethyl and the benzyloxy group is shown to be necessary for herbicidal activity in benzyloxytetrahydrofuran, 2) but there is no stereochemical consideration of the two oxygens in the molecule. Although syn-cinmethylin reportedly showed stronger herbicidal activity than the anti-isomer, 7) the biological activity of the two isomers has not been shown. In studies on benzyl ether-type herbicides, to our knowledge, there has been no discussion of the importance of the stereochemistry of the two oxygens to the level of herbicidal activity.…”

Biotransformation of 1,8-cineole, the main product of Eucalyptus oils

“…These oils have a recognized allelopathic action (Romagni et al 2000a;Romagni et al 2000b) for this reason its extraction before returning the leaves to the soil would be an ecologically advisable practice. Eucalyptus essential oil, that is commercialized at a price of U$S 3.5 Kg, can be easily obtained from leaves and branches by steam distillation (Clark, 2000).…”