Imazamox Absorption, Translocation, and Metabolism in Red Lentil and Dry Bean

Abstract

Imazamox is an imidazolinone herbicide used to control many grasses and broadleaf weeds in leguminous crops such as soybean, alfalfa, and dry bean; however, imazamox cannot be used on red lentil due to unacceptable injury. Studies were conducted to compare imazamox absorption, translocation, and metabolism in red lentil and dry bean to determine if any or all of these factors contributed to differential crop sensitivity. Radiolabeled imazamox was applied to three young red lentil leaves and the youngest, fully expanded dry bean trifoliolate leaf. Absorption, translocation, and metabolism were followed over a 96-h time course. Red lentil had more rapid absorption compared to dry beans with 64 and 54% of the applied dose absorbed 12 h after treatment (HAT), respectively. Maximum absorption was also greater in red lentil than dry bean, 79 and 61%, respectively. Translocation out of the treated leaf was significantly higher in red lentil compared with dry bean, 16 and 0.5%, respectively, at 96 HAT. Translocation was greater to red lentil roots compared to shoots, 9 and 7%, respectively, at 96 HAT. In dry bean only 14% of applied14C-imazamox remained intact 24 HAT, while 79% of the radioactivity was imazamox in red lentil 24 HAT. Both species metabolized the herbicide to more polar metabolites. The inherent sensitivity of aceolactate synthase (ALS) from dry bean and red lentil was also evaluated. ALS from both species had similar I50values for imazamox, 7.2 and 8.2 µM, respectively. The combined effects of increased imazamox absorption and reduced imazamox metabolism are the major contributors to differential selectivity between dry bean and red lentil. Rapid imazamox metabolism in dry bean significantly limited herbicide translocation out of the treated leaf.

Response of vetch, lentil, chickpea and red pea to pre- or post-emergence applied herbicides

“…Similar phytotoxicity symptoms have been reported in lentil to imazethapyr (Wall, 1996). According to Bukun et al (2012), the increased lentil susceptibility to imazamox, as compared with the other legumes, could be attributed to the combined effects of increased herbicide absorption and reduced metabolism. Chickpea injury caused by imazamox is in agreement with other studies reporting chickpea tolerance to imazamox and imazethapyr (Taran et al, 2010).…”

Physiological, biochemical and molecular characterization of an induced mutation conferring imidazolinone resistance in wheat

“…The latter two mechanisms are the most important and best investigated in crop plants and weeds (Duke 1996, Powles andYu 2010). Enhanced metabolism of IMIs has been studied in Myriophyllum spicatum, soybean, alfalfa and leguminous crops (Ohba et al 1997, Bukun et al 2012. In tolerant/resistant species, imazamox is metabolized by oxidative hydroxylation at the -carbon of the 5-methoxymethyl substituent on the pyridine ring, followed by carbohydrate conjugation (Ohba et al 1997).…”

Absorption and Penetration of Herbicides Viewed in Metabolism Studies: Case of Glufosinate and Imazamox in Wheat

“…In the case of imazamox, some authors have studied the presence of metabolites by the measure of radioactivity in extracts of plants treated with 14 C-imazamox (13,14) as target metabolites have not been commercialized. The absence of commercial metabolites has delayed research on degradation of the herbicide, which has been restricted to studies involving radioactivity-based methods (13,14) has required the synthesis of the target metabolites (15).…”

“…The absence of commercial metabolites has delayed research on degradation of the herbicide, which has been restricted to studies involving radioactivity-based methods (13,14) has required the synthesis of the target metabolites (15). Harir and his collegues (16), working with radioactivity-based methods, have measured the presence of metabolites through the amount of measured total radioactivity, which is not reliable information because the radioactivity can stem from a non-metabolic degradation occurring outside the plant by photolysis.…”

“…The capability of CE can be improved by coupling to a mass spectrometry (MS) detector, which has been the equipment used for several studies dealing with trace analysis of herbicides, including imazamox (18)(19)(20)(21). In addition to the use of CE, separation of imazamox from mixtures with other herbicides and pesticides has involved gas chromatography (GC) (22) and, particularly, liquid chromatography (LC) (13,14,23) with MS detection in all instances. Despite the potential of MS in the identification of degradation products from herbicides (16), no MS-based studies have been reported to confirm the presence of imazamox metabolites in plants.…”