Cell wall modifications in bean (Phaseolus vulgaris) callus cultures tolerant to isoxaben

Cultures of bean (Phaseolus vulgaris L.) callus were adapted for growth in a 12 mu M concentration of the herbicide isoxaben; 1200-fold greater than t he I-50 calculated, Tolerant calluses grew slower, were browner and harder than nontolerant ones and formed large globular corpuscles on their surface , Cell wall fractionation of tolerant cells indicated that the mechanism of adaptation depends an the ability. of these cells to divide and expand wit h a modified wall. The walls of tolerant cells growing on isoxaben differ f rom those of nontolerant cells by having reduced levels of cellulase and he micelluloses and a higher uronic acid content, These differences are alread y found in adaptations to low concentrations of isoxaben and keep to the hi ghest adaptation levels tested without any great change.