Translocation and distribution of eight C-¹⁴-Iabeled amino acids were studied in two closely related barley varieties, Atlas and Atsel. The compounds were: L-valine; DL-valine; DL-lysine; L-histidine; DL-phenylalanine; DL-tryptophan; DL-arginine; and glycine. For purposes of comparison, similar experiments were also conducted with labeled amitrole, 2,4-D, and monuron. Labeled compounds were applied either to leaves or roots of eight-day-old plants. For leaf experiments, 0.1 ?mole at 10^-2 M was applied; for root studies, 0.1 ?mole at 1^-6 M in 100 ml of nutrient solution. Autoradiographs were made after one, four, and 14 days.

The amino acids were accumulated in the bud tissues following application to either leaf or root, with a tendency for greater accumulation from leaf treatment.

Extraction and chromatography of labeled L-valine showed greatest extractibility and radioactivity 11 hours following application, and very little after that time. All amino acids tested showed greatest accumulation in bud tissues and root tips at the one-day time interval, indicating that these compounds must have nearly stopped translocating after one day. Results with tryptophan were not entirely satisfactory because of its low solubility. Root uptake was very slightly greater with the Atsel variety than with Atlas—a finding apparently not related to the presence of a greater amount of endogenous tryptophan in bud tissues of Atlas.

In comparison with the amino acids, 2,4-D showed an even more limited phloem distribution pattern. Translocation of 2,4-D from the treated leaf possibly lasted less than 11 hours. Amitrole, on the other hand, continued translocating from the leaf application to the extent that each new leaf emerging from the main axis in the 14-day interval was heavily labeled, and roots also became more heavily labeled with increasing time. Monuron exhibited apoplastic mobility.