Chlorsulfuron tolerance and acetolactate synthase in maize (Zea mays) inbred lines

Seven corn inbred lines previously shown to differ in response to soil residues of chlorsulfuron were characterized as to the target-enzyme acetolactate synthase (ALS) specific activity and to its susceptibility to the herbicide. ALS from plantlets at the five-leaf stage of growth was similarly susceptible to chlorsulfuron in all lines and its specific activity in the shoots was not significantly correlated with in vivo tolerance to the herbicide. By contrast, differences in ALS specific activity in roots of plants both at the five- and three-leaf stages of growth were significantly correlated (r = 0.96** and r = 0.93**, respectively) with in vivo tolerance. Correlation was also noted in extracts from cultured excised root tips (r = 0.94**). Callus tissue of a chlorsulfuron-tolerant line was less affected by the herbicide and had a significantly higher ALS specific activity than callus from a chlorsulfuron susceptible line, whereas inhibition of ALS by the herbicide was similar in both lines. These results indicate that the naturally occurring differences in. ALS levels in the roots of the investigated inbred lines contribute largely to the differential in vivo response observed to chlorsulfuron