Uptake, Cellular Distribution, and Metabolism of ¹⁴C‐picloram by Excised Plant Tissues

Excised soybean ( Glycine max (L.) Merr.) hypocotyls, barley ( Hordeum vulgare L.) coleoptiles, barley leaf sections, and Canada thistle ( Cirsium arvense (L.) Scop.) leaf discs continuously absorbed 14 C‐picloram from a buffered solution over a 24 h period. After an 8 h uptake period excised sections released up to 30 % of the absorbed picloram into ‘clean’ buffer solution in a 4 h period. Leaf sections released less than did the other tissues. Uptake of 14 C‐picloram by soybean hypocotyl and barley coleoptile sections increased with an increase in temperature from 5 to 35°C. Uptake was promoted by added ATP and sucrose but inhibited by actinomycin D, cycloheximide, and DNP. After differential centrifugation of aqueous extracts of 14 C‐picloram‐treated excised tissues more than 95 % of the radioactivity was in the soluble fraction. In excised barley and Canada thistle leaf tissues, 3 days after treatment, part of the 14 C‐picloram was conjugated with plant constituents, largely with sugar(s). After acid hydrolysis of ethanol extracts of such tissues only unaltered picloram was detected. In barley coleoptile and soybean hypocotyl sections no conjugation products of 14 C‐picloram were detected.