Basis of selectivity of cyhalofop-butyl in Oryza sativa L.

Abstract

Cyhalofop-butyl (CB), 2-[4-(4-cyano-2-fluorophenoxy)phenoxy]propanoic acid, butyl ester (R), is an aryloxyphenoxypropionate (AOPP) herbicide for postemergence use in rice to control grasses, mainly Echinochloa spp. Similar to other AOPP and cyclohexanedione herbicides, the site of action of CB is acetyl-coenzyme A carboxylase (ACCase), an enzyme in fatty acid biosynthesis. The mechanisms involved in the selectivity of CB in rice (Oryza sativa L.)-absorption, translocation, metabolism, and ACCase susceptibility-were studied. Studies of in vitro inhibition of ACCase in E. oryzoides and O. sativa L. species discounted any differential active site sensitivity as the basis of tolerance to CB. The O. sativa L. cuticle was uniformly covered by waxes, with predominantly unshaped large waxes randomly distributed, obtaining absorption values of under 30%, 24 h after application (HAA). The E. oryzoides cuticle formed a non-uniform covered reticule, with less wax density and areas lacking in waxes reaching maximum values of absorption rising to 73%, 24 HAA. Translocation studies revealed no significant differences, either between species, or between times, remaining in the treated leaf. There was a good correlation between the rate of metabolism and plant tolerance. Plant metabolism studies demonstrated that tolerant rice inactivated the esterases producing a lack of functionality thus reducing the conversion of CB to cyhalofop acid, which is the active form of the herbicide. Moreover, it increased the metabolism of the herbicide forming non toxic metabolites much faster than E. oryzoides. It was concluded that the basis of rice tolerance to CB was a lack of esterase functionality, a reduced absorption through the cuticle and an increase in cyhalofop acid metabolism.

Antioxidant activity of rice plants sprayed with herbicides

“…Studies demonstrate that the fluazifop-P-butyl herbicide, belonging to the same group of cyhalofop-butyl, can cause lipid peroxidation in grasses (Luo et al 2004). However, rice characteristics such as lack of esterase functionality, reduced absorption through the cuticle and increase in herbicide metabolism may help to explain the selectivity of rice after the application of cyhalofop-butyl (Ruiz-Santaella et al 2006).…”

“…Cyhalofop-butyl acts by inhibiting acetylcoenzyme A carboxylase, reducing the ability of plants to produce malonyl-coenzyme A, which is needed for the synthesis of fatty acids (Ruiz-Santaella et al 2006). Fatty acids are essential constituents of plasma membranes of cells and organelles.…”

Role of a Carboxylesterase in Herbicide Bioactivation in Arabidopsis thaliana

“…Studies with herbicide-resistant and -susceptible weed populations (7) and metabolism studies with crops and wild grasses (8) have correlatively pointed to the importance of esterase-mediated hydrolysis in herbicide bioactivation. Using Arabidopsis as a plant model, our molecular genetic studies demonstrate that a single CXE can confer this bioactivation trait and determine herbicide sensitivity.…”

“…In the latter case, many major classes of herbicides are applied as esters to facilitate penetration into the leaf. Ester hydrolysis within the leaf is then required to bioactivate the herbicide, and the rate of cleavage is an important determinant of selective action in crops and weeds (7,8). Using a classification system based on the sensitivity of hydrolases to inhibition by organophosphate insecticides, herbicide-active CXEs in wheat and competing grass weeds are of the B-type (9,6).…”

Susceptibility of Echinochloa populations to cyhalofop-butyl in Southern region of Brazil and impact of the weed phenology on its efficacy of control

“…As all the other aryloxyphenoxypropionate acids, it works by inhibiting the Acetyl Coenzyme A Carboxylase enzyme, which catalyzes the first synthesis route of oily acids (DÉLYE et al, 2003). It has physicalchemical characteristics that result into high selectivity over rice, due to low esterification and high metabolization of its molecules (RUIZ-SANTAELLA et al, 2006a). Conversely, it is very active on other grasses, such as the ones from the Echinochloa complex, giving high effectiveness to rates starting from 200g ha -1 (KIM et al, 2005).…”