Detoxification of Atrazine in Three Gramineae Subfamilies

Abstract

Inhibition and subsequent recovery of net CO 2 exchange (NCE) by single leaves of 53 grass species of the subfamilies Festucoideae, Panicoideae, and Eragrostoideae was monitored following limited root uptake of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)- s -triazine]. Rates of NCE recovery were correlated with rates of 14 C-atrazine metabolism in leaf sections of festucoid and panicoid grasses but not eragrostoid grasses. Rates of NCE recovery among the nine festucoid and 12 eragrostoid species tested did not exceed 0.2 and 1.1 mg CO 2 per dm 2 per hr/hr, respectively, whereas for the 31 panicoid species, it ranged from 0.2 to 2.4 mg CO 2 per dm 2 per hr/hr. Selected species exhibiting NCE recovery rates exceeding 1.2 mg CO 2 per dm 2 per hr/hr were tolerant to 1.0 kg/ha preemergence and 1.25 kg/ha postemergence atrazine applications. These panicoid species included a number of common weed species belonging to the genera Digitaria, Panicum , and Setaria , as well as species belonging to Bracharia, Pennisetum, Sorghum , and Zea. Unchanged 14 C-atrazine accounted for 11.3 to 92.7% of the total 14 C-radioactivity extracted from 14 C-atrazine infiltrated leaf sections following an 8-hr incubation period. N-dealkylation, hydroxylation, and peptide conjugation occurred in all species, although rates of these metabolic pathways varied widely among species. Recovery of NCE was correlated with formation on the glutathione-atrazine conjugate, and conjugation was the major detoxification pathway in species exhibiting tolerance to atrazine.