Responses of Crop Plants to O-Isopropyl N-Phenyl Carbamate

Thirteen monocotyledonous species treated with O-isopropyl N-phenyl carbamate at the germination stage showed similar gross responses to the compound. These were characterized by lack of root and shoot elongation, with concurrent swelling of these parts. The roots were stubby and bulbous, and the coleoptilar region was markedly swollen. 2. Young established cereals treated by soil application of the carbamate ceased to grow acropetally, and the leaves became dark green. In contrast to responses induced by applications of 2,4-dichlorophenoxyacetic acid, no epinasty occurred. 3. Of thirty-nine dicotyledonous species exposed to O-isopropyl N-phenyl carbamate at the germination stage, fifteen showed some responses to the compound. Plants of six of these species largely recovered from the treatment, whereas in nine they were permanently inhibited. All the latter species responded similarly in that the hypocotyl failed to elongate normally and became enlarged. The root system was much stunted, and in some species, such as buckwheat, flax, and morning-glory, only a radicle emerged. Most of the species responding to the carbamate developed to the two-leaf stage, but the cotyledons never fully expanded, and the stem apex failed to grow. 4. Applications of the carbamate to the tops of oat plants in the boot stage of development resulted in cessation of panicle growth, whereas similar applications at the seedling stage induced no responses. The relation of these responses to stage of plant development and certain implications regarding the use of other similar growth-regulators are discussed. 5. Marked abnormal cytological behavior occurred in the roots and shoots of oat and barley plants treated with O-isopropyl N-phenyl carbamate. This was characterized by an interrupted mitotic cycle, blocked metaphases, multinucleate cells, occurrence of giant nuclei, and a highly increased chromosome number in certain cells of both root and shoot. Cell division ceased in the apical meristems of root and shoot. Great cell enlargement and maturation occurred in these cells and in those in the process of expansion. 6. The abnormal cytological behavior occurring in the root and shoot of oat and barley plants treated with the carbamate can be correlated with subsequent survival of the plants or with abnormal development. Short-time exposure studies revealed that, as the cytological effects became more pronounced, the number of plants surviving to maturity was markedly reduced. 7. Possible agronomic applications of growth-regulators similar to O-isopropyl N-phenyl carbamate for vegetational control are suggested, as well as the probable usefulness of this carbamate in genetic and cytological studies of cereals and certain grasses.