Translocation and Complex Formation of Root‐applied 2,4‐D and Picloram in Susceptible and Tolerant Species

Translocation and complex formation of 14 C‐labelled 2,4‐dichlorophenoxyacetic acid (2,4‐D) and 4‐amino‐3,5,6‐trichloropicolinic acid (picloram) in seedlings of sunflower ( Helianthus annuus L. var. uniflorus ), rape ( Brassica napus L. cv. Nilla), wheat ( Triticum aestivum L. cv. Starke), and Norway spruce ( Picea abies (L.) H. Karst.) were studied. The herbicides were absorbed through the roots from the nutrient solution, Picloram was well translocated to the shoots of the four species; while the acropetal translocation of 2,4‐D was small except in rape. In 2,4‐D‐susceptible sunflower and rape and in picloramsusceptible sunflower and spruce the herbicides were recovered mainly in the uncomplexed form. In 2,4‐D tolerant wheat and spruce most of the absorbed 2,4‐D was converted into water‐soluble or TCA‐insoluble complexes. In picloram‐tolerant wheat and in relatively picloram‐tolerant rape, the absorbed picloram was also converted into complexes recovered predominantly in the water‐soluble fraction. Most of the complexes released free herbicides by hydrolyzing in NaOH or HCI. The results further support the hypothesis that complex formation counteracts herbicide toxicity.