Effects of some growth substances on mitosis.

Radiomimetic action of growth substances, also called hormones, has been demonstrated by several workers Some of the growth substances are used as growth promotors while others are used as herbicides for weed control. As they prove toxic beyond certain concentrations, it is fruitful to study their effects at different concentrations. This paper describes the results of an experiment involving different concentrations of three growth sub stances on root tip mitosis in Vicia faba when treated for varying durations. Materials and methods Three growth substances namely, Gibberellic acid-GA (a naturally occurring phytohormone), Indole-butyric acid-IBA (a synthetic hormone) and 2, 4-Dichioro phenoxyacetic acid-2, 4-D (a synthetic hormonic herbicide) were taken for this study. The seeds of Vicia faba were grown in petri dishes on blotting papers. When the roots attained the length of about 2cm, treatments were given by the aqueous solu tions of the chemicals, the concentrations being 10 and 50ppm. The durations of treatments were 3, 6 and 12 hours with a recovery period of 12 hours for each treat ment. Root tips were collected in 3: 1 alcohol-acetic acid solution and stored in 70 per cent alcohol. Slides were prepared using 0.5 per cent haematoxylin stain and examined under microscope. Results The cell metabolism was strongly disturbed by 2, 4-D. The protoplasm became gelated with higher concentration and the cell contents disappeared. IBA also caused some toxic effects like 2, 4-D while GA had no such effect. Data relating to comparative effects of these chemicals on cell division are shown in Table 1 and graphically presented in Fig. 1. GA caused increase in mitotic index with increasing duration at 10 ppm concentration. Frequency of dividing cells was 25.3 per cent after 12 hours treatment in contrast to 14.1 per cent in control. At 50ppm concentration, mitotic index decreased with increasing durations, however,