Submitted to: Pesticide Biochemistry and Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/22/2002
Publication Date: 4/10/2002
Citation: Hirase, K., Molin, W.T. 2002. Differential cysteine synthase activity and alachlor susceptibility in five crop and six weed species. Journal of Pesticide Biochemistry and Physiology 72:169-177. Interpretive Summary: This paper characterizes crops and weeds with respect to their concentrations of cysteine synthase, an enzyme involved in sulfur metabolism, and thiols, which are compounds containing sulfur. The levels of the thiols, cysteine and glutathione, are important in the detoxification of some herbicides such as alachlor. The susceptibility of these weeds to the herbicide alachlor was then determined and found to be best correlated with the levels of cysteine synthase rather than the thiol concentrations. These results suggest that tolerance to alachlor may be more related in a plants ability to produce thiols rather than the actual levels of thiols.
Technical Abstract: Cysteine synthase (CS; EC 18.104.22.168) activity was compared among crops and grass weeds having different susceptibilities to alachlor. The order of alachlor tolerance of 11 grass species from most to least was: corn>>barley = rice = wheat>sorghum = johnsongrass = broadleaf signalgrass>barnyardgrass = large crabgrass> green foxtail = goosegrass, suggesting that corn was tolerant and all other species were susceptible to alachlor. In shoots, rice had the highest extractable CS activity (44.3 umol/min/g fresh weight) and corn, barley, wheat, sorghum, johnsongrass and broadleaf signalgrass had the second highest activity ranging between 20.6 and 26.4 umol/min/g fresh weight. CS activity of large crabgrass, green foxtail and goosegrass was relatively lower (15.5 to 18.1 umol/min/g fresh weight). Generally, levels of CS activity in roots were similar to those in shoots in each grass species. However, barley had lower root CS activity than that in shoots and green foxtail had higher root CS activity than in shoots. Alachlor treatment (GR50 concentrations) had no effect on extractable CS activity in shoots of corn, barley, sorghum and barnyardgrass. Content of non-protein cysteine in shoots ranged between 60.1 and 131.5 nmol/g fresh weight, and was not largely different among the grass species except for green foxtail where it was high, i.e., 334.6 nmol/g fresh weight. Content of other non-protein thiols was highest in corn (574.7 nmol/g fresh weight) which was tolerant to alachlor, and the contents were relatively low in other grass species which were susceptible.