Translocation and Complex Formation of Picloram and 2,4-D in Wheat Seedlings

Uptake, translocation and metabolism of ¹⁴C-labelled 4-amino-3,5,6-trichloropicolinic acid (picloram) and 2,4-dichlorophenoxyacetic acid (2,4-D) in seedlings of wheat (Triticum aestivum L.) were studied. The uptake of the herbicides through the upper surface of the first leaf was slow but was almost complete after nine days. Picloram was absorbed faster than 2,4-D. Picloram was also translocated into the stem and the untreated leaves to a greater extent than 2,4-D. Only small fractions of the activity were recovered from the roots and from the nutrient solution. Picloram and 2,4-D formed water-soluble conjugates in the tissues. These conjugates were very labile and hydrolyzed under release of the unchanged herbicides. The isotope from 2,4-D was also incorporated in an insoluble fraction, containing cell walls and proteins. Also from this fraction biologically active 2,4-D could be released by hydrolysis. The formation of the complexes was partly prevented by cycloheximide. It is suggested that herbicide detoxification through complex formation is of importance for the relatively low sensitivity of wheat to auxin herbicides.