Morphological and Histological Effects of Trifluralin on Root Development

The most obvious external effect of trifluralin on the primary root was an increase in the amount of radial expansion near the root tip. The initial radial expansion of the treated roots occurred in the region of maximum elongation. With increased duration of treatment there was a gradual decrease in the extent of the meristematic tissue zone because of progressive vacuolation and subsequent differentiation. Although trifluralin disrupted the mitotic process, no one type of mitotic figure prevailed. Mitotic activity was not affected in all of the cells, some of which appeared to be undergoing a perfectly normal mitosis. Rates of trifluralin application sufficient to inhibit lateral root emergence without interfering with development of the primary root affected the pericycle and portions of the endodermis. The pericyclic cells were much enlarged in. the regions opposite the protoxylem and had undergone some of the initial phases of lateral root formation. These enlarged pericyclic cells correspond to what have been called primordiomorphs.