Étude de l'action d'un herbicide, le chlorthal, sur la prolifération cellulaire et la croissance de la tige du Cuscuta lupuliformis

Abstract

The effects of a herbicide, chlorthal (2,3,5,6-tetrachloroterephthalic acid), on the growth and development of Cuscuta lupuliformis Krocker have been examined on seedlings 2 to 15 days old. In dodder, the shoot meristem is not restricted to the apex where rudimentary leaves are initiated but extends approximately 6 mm downwards, to the hook zone of the young stem. In this region, cell dimensions, values of the mitotic indices, and the distribution of the nuclear DNA contents measured by microspectrophotometry remain essentially unchanged. Beyond the hook zone, cell elongation gradually replaces cell division. A chlorthal treatment caused a reduction in the mitotic indices of the meristematic cells along with a temporary blocking of mitoses at metaphase. These effects were similar to those observed with colchicine treatments. The nuclei were then reconstituted with 4C DNA contents and, after several new cycles under which DNA was replicated normally, they became polyploid. After 15 days of herbicide application, the meristematic apex and the underlying zones exhibited numerous hypertrophied cells with nuclear DNA contents of 8, 16, 32, and 64C. There is evidence that chlorthal stops cellular division without inhibiting the other phases of the cell cycle; it induces a rapid arrest of the growth of the young dodder.