EFFECT OF IMAZAMETHABENZ ON HISTOLOGY AND HISTOCHEMISTRY OF POLYSACCHARIDES IN THE MAIN SHOOT OF WILD OAT (AVENA-FATUA)

Imazamethabenz, an acetohydroxyacid synthase (AHAS)-inhibiting herbici de, was applied at a sublethal rate (2.00 g al ha-1) to foliage of gre enhouse-grown wild oat plants at the 2-leaf stage without tillers. Mai n shoot tissues were sampled 1 to 2 wk after imazamethabenz treatment and prepared for light microscopic examination. Histological observati ons showed that imazamethabenz treatment did not produce drastic chang es on leaf structures.but did affect chloroplast integrity of fully ex panded 2nd leaf and inhibited differentiation of the young 3rd leaf 1 wk after application. The internode length and the number of cells in internodes of the herbicide-treated main stem were greatly reduced, pr esumably due to the inhibition by imazamethabenz of intercalary merist em cell division in early stages of internode elongation. One week aft er imazamethabenz application, histochemical studies revealed an incre ased accumulation of starch granules in chloroplasts of the 2nd leaf b ut reduced starch levels in the main stem. This confirmed the hypothes is that AHAS inhibitors affected phloem transport of photosynthates.