Effect of Imazamethabenz on Histology and Histochemistry of Polysaccharides in the Main Shoot of Wild Oat (Avena fatua)

Imazamethabenz, an acetohydroxyacid synthase (AHAS)-inhibiting herbicide, was applied at a sublethal rate (200 g ai ha–1) to foliage of greenhouse-grown wild oat plants at the 2-leaf stage without tillers. Main shoot tissues were sampled 1 to 2 wk after imazamethabenz treatment and prepared for light microscopic examination. Histological observations showed that imazamethabenz treatment did not produce drastic changes on leaf structures but did affect chloroplast integrity of fully expanded 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, presumably due to the inhibition by imazamethabenz of intercalary meristem cell division in early stages of internode elongation. One week after imazamethabenz application, histochemical studies revealed an increased accumulation of starch granules in chloroplasts of the 2nd leaf but reduced starch levels in the main stem. This confirmed the hypothesis that AHAS inhibitors affected phloem transport of photosynthates.