Absorption, translocation and metabolism of isoxaflutole by tolerant and susceptible plant species
Experiments were conducted to study the extent of absorption, translocation and metabolism of ring labeled 14C-isoxaflutole [5-cyclopropyl-4-(2-methylsulphonyl-4-trifluromethyl benzoyl)isoxazole] in order to explain its differential response in velvetleaf (Abutilon theophrasti Medicus), yellow foxtail [ Setaria lutescens (Weigel)], and two corn (Zea mays L) hybrids. Seedlings were grown under controlled environment. Seedlings were harvested 3, 6, 12, 24, 48, 72, 96 and 120 hours after treatment (HAT) and sectioned into root, shoot/stalk and leaves.
Absorption of root applied radioactivity was 135.6 (120 HAT) and 230 (96 HAT) disintegration per minute (dpm) mg−1 fresh weight in velvetleaf and yellow foxtail, respectively. The translocation of root absorbed 14C-isoxaflutole to shoot was 83.6% (120 HAT) in velvetleaf and 93% (72 HAT) in yellow foxtail. When applied to the yellow foxtail foliage, absorption was maximum 24 HAT and translocation of 14C-isoxaflutole from treated leaf to other plant parts reached its peak at 48 HAT (33.4%). Based on Rf values, applied radioactivity was partitioned into isoxaflutole (Rf = 0.91), diketonitrile metabolite (Rf = 0.62), unknown metabolite ‘A’ (Rf = 0.49) and benzoic acid (Rf = 0.29). Yellow foxtail had more benzoic acid content (21.08%) than the benzoic acid content (12.85%) in velvetleaf. The active herbicide fraction (total of diketonitrile metabolite and unknown metabolite ‘A’) was more in velvetleaf (80.2%) than in yellow foxtail (69.9%). The presence of high level of active herbicide fraction in velvetleaf may explain its susceptibility to isoxaflutole.
Absorption of root applied 14C-isoxaflutole was more in Pioneer-3751 corn hybrid (52.1 dpm mg−1 fresh weight in 24 h) than in Pioneer-3394 corn hybrid (37.5 dpm mg−1 fresh weight 24 h). However, absorption of 14C-isoxaflutole and its subsequent translocation from root to shoot reached its peak 96 HAT in two corn hybrids. Both corn hybrids were equally tolerant to isoxaflutole. Benzoic acid contents in the P-3394 and P-3751 (24.57 and 25.57%, respectively) were similar, while the active herbicide fraction was also similar (63.7% and 67.8%) in P-3394 and P-3751.