Root Absorption and Translocation of Picloram by Oats and Soybeans

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Abstract
The effects of time, concentration, pH, temperature, and metabolic inhibitors on 4-amino-3,5,6-trichloropicolinic acid (picloram) uptake from nutrient solution by oats (Avena sativaL. ‘Markton’) and soybeans (Glycine maxL. ‘Lee’) were studied. Oats and soybeans had similar absorption patterns of rapid initial uptake. However, total accumulation patterns markedly differed in that accumulation was concentration-dependent for oats but not for soybeans. Initial uptake by oats and soybean roots increased as solution concentration increased. Picloram was redistributed in oats and soybeans and some egress from roots to solution occurred. Picloram uptake by both plant species was markedly diminished with an increase in pH from 3.5 to 4.5, but pH had little effect from 4.5 to 9.5. Less picloram was taken up by oats and soybean roots from solution maintained at 4 C than at 26 C. Translocation to tops followed a similar trend. Increasing concentrations of three metabolic inhibitors, 2,4-dinitrophenol (DNP), sodium azide, and sodium arsenite, reduced root uptake of picloram in both species. All inhibitors (except DNP for oats) at 10−6to 10−5molar concentrations stimulated translocation of picloram to oats and soybean tops while higher concentrations depressed translocation.