Herbicidal Concentrations of Picloram in Cell Culture and Leaf Buds

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Abstract
Cell cultures of soybean(Glycine max(L.) Merrill ‘Acme’) were exposed to media containing 4-amino-3,5,6-trichloropicolinic acid (picloram) for 15 days. Picloram also was supplied once in droplets (water) to cotyledons of 10 to 13-day-old seedlings of cotton(Gossypium hirsutumL. ‘Champion’). The amounts of picloram necessary to reach and exceed the 50% tolerance limit (TL50) of the cell cultures (inhibition) and of the primary leaf buds (toxicity) were established, and internal picloram concentrations then were determined. Internal concentrations at the TL50were 0.17 nM/g fresh weight and 14.7 nM/g fresh weight for cell cultures and leaf buds, respectively. These values are approximately 10−7and 10−5molar. In leaf buds, concentrations increased rapidly for 36 hr after treatment and declined slowly thereafter. Primary leaf buds accumulated up to several times the lethal internal concentration of picloram when the dosage to the cotyledons was increased by one order of magnitude.