Effect of 2,4-dichlorophenoxyacetic acid on nuclear division in stem segments ofPisum sativum L. cultivatedin vitro

We have investigated the influence of 2,4-dichlorophenoxyacetic acid (2,4-D) on the appearance of nuclear fragments, caused by direct nuclear division, as well as on mitotic activity in cultivated internodial stem segments ofPisum sativum L., cv. Bördi, during 180 d of cultivation. Direct nuclear fragmentation (dNF) was indicated by the shape and structure of the nucleus as well as by the occurrence of 1C- and 3C-values of DNA, investigated cytophotometrically. The dNF occurred during the whole cultivation period in segments treated by 2,4-D in concentrations from 4 to 32 mg 1^?1. In the presence of 2 mg 1^?1 of 2,4-D the dNF existed in the explants only up to 90 d. Mitotic activity was not observed in the 2,4-D-free control but occurred during the whole cultivation period when 2,4-D was added in concentrations from 2 to 16 mg l^?1. In the presence of 32 mg l^?1 of 2,4-D the level of mitotic activity was very low at the beginning and ceased after 60 d in culture.