Herbricide-inhibited phosphoenolpyruvate carboxylase in leaves of six nonsucculent scrub species

Abstract

The influence of two herbicides, paraquat or 2,4,5-T on the in vitro as well as in vivo activity of phosphoenolpyruvate carboxylase from leaves of six nonsucculent scrub species was investigated. The plants, all native and important constituents of the scrubland vegetation, included Carissa spinarum L., Maba buxijoliaCl., Flacourtia sepiariaRoxb., Chomelia asiaticaO. Kze., Gymnosporia emarginataLaws., and Dodonaea viscosa L. The in vitro activity of the enzyme from untreated leaves of all species was inhibited when the purified leaf extracts were incubated in herbicide solutions. Foliar application of 100 mg of paraquat or 2000 mg of 2,4,5-T per liter also inhibited the enzyme activity of purified leaf extracts at 72 h after herbicide treatment in all the species tested. The inhibition of the in vitro as well as in vivo enzyme activity was more prominent with paraquat than with 2,4,5-T treatment. It is suggested that the inhibition of this major carboxylating enzyme activity may be involved in the herbicide inhibition of carbon dioxide fixation in leaves.