Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Abstract

Susceptibilities of different test systems from maize (Zea mays), Poa annua, and Festuca rubra to herbicides that inhibit the enzyme acetyl-coenzyme A carboxylase.

Abstract

Laboratory studies were conducted to determine the susceptibilities of maize (cv. Champ) and the herbicide-resistant grass species, Poa annua (annual meadow grass) and Festuca rubra (red fescue), to quizalofop, fluazifop and sethoxydim, in leaf blades and isolated chloroplasts, and by assaying acetyl-coenzyme A carboxylase (ACCase) in desalted leaf homogenates. The resistance of P. annua and F. rubra appeared to be at the level of ACCase. Festuca rubra ACCase was highly insensitive and P. annua ACCase was partially insensitive to the herbicides. Fatty acid synthesis in isolated maize chloroplasts was more susceptible to inhibition than ACCase activity from whole leaves. There was a smaller difference in sensitivity between these 2 test systems in P. annua. The developmental pattern of ACCase-specific activity and its inhibition by quizalofop was measured in maize and P. annua leaf blades. There was an age-dependent increase in the sensitivity of maize leaf ACCase activity to inhibition by quizalofop. Together with the greater susceptibility of chloroplasts compared with leaf homogenates, these results could imply that a herbicide-insensitive (extra-chloroplastic) ACCase isoform was less highly expressed in older leaves. Poa annua ACCase did not significantly alter in sensitivity as leaves aged, consistent with the smaller difference in the level of inhibition between chloroplasts and leaf homogenates in this species. A small pyruvate carboxylase activity was detected in maize leaves after 9 days. By 38 days, when leaves were senescing, pyruvate carboxylase activity predominated over ACCase.