UPTAKE, TRANSLOCATION, AND METABOLISM IN ALFALFA (MEDICAGO-SATIVA) SELECTED FOR ENHANCED TOLERANCE TO TERBACIL

Terbacil tolerance was investigated in field-selected alfalfa strain ' OK 182.' Growth response studies indicated a 78% increase in tolerance over the unselected parental cultivar 'Cimarron.' Photosynthetic elec tron transport was inhibited similarly in both cultivars when isolated thylakoids were exposed to a wide range of terbacil concentration ind icating that tolerance was not due to reduced sensitivity at the site- of-action. 'OK 182' took up an average of 22% less C-14-terbacil over the 6-d labeling period. A similar proportion of total radiolabel was translocated in both strains indicating that differential translocatio n was not a factor in the tolerance mechanism. Once in the leaves, ter bacil was rapidly metabolized to a glucosidic conjugate by both strain s. Terbacil and total concentration of metabolites in leaf tissues wer e 17% and 33% lower in 'OK 182' than in 'Cimarron,' respectively. Enha nced tolerance to terbacil in 'OK 182' was attributed to decreased ter bacil uptake.