Uptake of Herbicides by Soybean Roots in Culture Solutions

Abstract

Uptake of herbicides by excised roots of soybean(Glycine max(L.) Merr.) plants was studied over periods of 30 min, 8 hr, and 48 hr. In the 48-hr experiment, initial rate of herbicide uptake was rapid and was greater at higher temperatures and external herbicide concentrations. Rates of initial uptake varied among herbicides. Over 30-min periods, rapid herbicide uptake by excised roots for 2.5 to 5 min was followed by much slower uptake. Total uptake for 30 min and 1 hr was in the order of 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea(linuron) > isopropyl-m-chlorocarbanilate (chlorpropham) >S-ethyl dipropylthiocarbamate (EPTC) > 3-amino-2,5-dichlorobenzoic acid (amiben) > 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine). However, total uptake after 48 hr was in the order of chloropropham > linuron > EPTC > atrazine > amiben, indicating that rates of uptake for the herbicides changed over 48 hr. Values of Q10for herbicide uptake were always less than 1.85, indicating that physical processes were important in uptake of herbicides by excised soybean roots. Uptake of herbicides over 8 hr by roots of intact plants was similar at 5, 10, and 20 C to uptake by excised roots, but uptake at 30 C was less for roots of intact plants than for excised roots. Transpiration increased as temperature increased, but herbicide uptake and transpiration were unrelated.