AbstractThe distribution of 2.5 mM‐14CMCPAMCPA = (2‐methyl‐4‐chlorophenoxyacetic acid).and 14CMCPBMCPB = (4‐(2‐methyI‐4‐chlorophenoxy) butyric acid).formulated as sodium salts with 0.05 tergitol, have been investigated when applied to an isolated leaf/agar block sink system ofVicia fabaL. Results are presented which show the effect on absorption and translocation of method of application, age of treatment leaf, treatment period, pretreatment with 5 μM ATP and removal of cuticle wax by chloroform wipe treatment. Significant negative correlations between cuticle wax fixation/translocation and leaf tissue content/translocation were recorded for both compounds, particularly MCPB, suggesting the involvement of both physicochemical and metabolic components in the process of absorption and translocation. The nature of the mechanisms involved was further investigated using isolated cuticle/epidermal systems and tightly‐coupled mitochondria isolated from roots ofV. fabaL. The results suggest that non‐movement of MCPB in this species is largely due to its enhanced retention within the cuticle and to the fact that it is a more effective uncoupler of oxidative phosphorylation than MCPA. The importance of these findings in terms of the relative efficiency of translocation of MCPA and MCPB when applie
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