Uptake, transport and metabolism of 14C-2,4-dichlorophenoxyacetic acid (14C-2,4-D) in cucumber (Cucumis sativus L.) explants

The uptake, distribution and metabolism of 2,4-D using 14C-labelled 2,4-dichlorophenoxyacetic acid (14C-2,4-D) was studied in isolated hypocotyl and cotyledon explants of cucumber (Cucumis sativus L.) in vitro. Cotyledons had a higher uptake capacity than hypocotyls; the uptake in cotyledons increased linearly up to 20 h, while in hypocotyls only up to 8 h. The distribution of 14C-activity in both organs was basipetal, but more pronounced in cotyledons. The 2,4-D taken up by cotyledons was metabolized very rapidly: only 7% of 14C-activity was associated with free 2,4-D after 20 h exposure. Hypocotyls metabolized 2,4-D more slowly: after 20 h 50% of the 14C-activity was still associated with free 2,4-D. After short incubation periods (2–5 h) 2,4-D-aspartate was a predominant metabolite, after longer incubation (8–20 h) 2,4-D-glucosyl ester prevailed. Roots or callus were formed on the base of cotyledons depending on the length of exposure to 2,4-D.