Uptake and translocation of some pesticides by hypocotyls of radish seedlings

Some of the factors affecting absorption and translocation of pesticides by the hypocotyls of intact radish (Raphanus sativus, L., cv. Black Spanish) seedlings have been studied, particular attention being given to the triazine herbicides simazine, atrazine and atraton. Uptake and translocation appear to be largely passive processes and by contrast with foliar absorption seem to be unaffected by humidity, con-centration, light and by the aqueous solubilities of the compounds. Diffusion across the tissues of the hypocotyl, rather than rate of transpiration, appears to determine the rate at which atrazine and simazine are translocated to the cotyledons. For several pesticides there is a qualitative relationship between the percentages of the compounds translocated to the upper portion of the shoots and their partition coefficients in oil/water systems. In conclusion, some consideration is given to the relative importance of uptake by roots and shoots under field conditions.