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

The uptake, distribution and metabolism of 2,4-D using C-14-labelled 2,4-di chlorophenoxyacetic acid (C-14-2,4-D) was studied in isolated hypocotyl and cotyledon explants of cucumber (Cucumis sativus L.) in vitro. Cotyledons h ad a higher uptake capacity than hypocotyls; the uptake in cotyledons incre ased linearly up to 20 h, while in hypocotyls only up to 8 h. The distribut ion of C-14-activity in both organs was basipetal, but more pronounced in c otyledons. The 2,4-D taken up by cotyledons was metabolized very rapidly: o nly 7% of C-14-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 C-14-activ ity 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 th e base of cotyledons depending on the length of exposure to 2,4-D.