CHLORSULFURON REDUCES EXTENSION OF WHEAT ROOT-TIPS IN LOW-ZINC SOLUTION CULTURE

Root tip extension was used as a measure of wheal root response to exp osure to the sulfonylurea herbicide chlorsulfuron. Plants pre-grown in low-zinc (0.2 mu M ZnHEDTA) solutions were placed in a perspex chambe r with nutrient solution on both sides of a partition separating the r oot tip from the rest of the plant. The root tip was exposed to differ ent concentrations of chlorsulfuron and observations were made during 22 h. Increasing the concentration of zinc in the solution around the root tip to 4 mu M ZnHEDTA did not alter root tip extension in the abs ence of chlorsulfuron. Significant decreases in root growth after 22 h were obtained with concentrations of 120 mu g chlorsulfuron 1(-1) and greater. Increasing the Zn concentration from 0.2 to 20 mu M ZnHEDTA in the nutrient solution around the root tip decreased control root gr owth but stimulated chlorsulfuron-treated roots to extend at the same rate as chlorsulfuron-free control plants. Adding Zn and chlorsulfuron to the more mature root parts above the root tip partition did not si gnificantly influence root tip extension. It is concluded that chlorsu lfuron inhibits wheat root growth and that increased Zn concentrations can alleviate or prevent the deleterious effects of chlorsulfuron. (C ) 1998 Annals of Botany Company.