is essentially the same as described in a previous paper (2). The air flow rate through each train can be checked and adjusted independently by means of a bypass manifold attached to a flowmeter. Respiratory CO2 from each flask was continuously swept out by a stream of CO.,-free air and absorbed in individual CO, traps. Flasks were shaken continuously in the light for six hours at 260 C. The respiratory CO., samples obtained during an experiment were precipitated as BaCO1 and the radioactivity determined with a thin mica window GAI counter (1.8 mg per cm2). At the end of a 6 hour incubation period, sections were removed from the me(lium, rinsed with water, and homogenized with 25 ml ethyl alcohol. The radioactivity of the medium, alcohol extract of the tissues, and the alcohol insoluble residue were also determined by the conventional method in order to get necessary information on total C14 recovery. Total glucose uptake by stem tissues was calculated from the summation of radioactivity found in respiratory C0, alcohol insoluble residue and alcohol extract. In general, eight separate flasks (two stem samples from untreated plants ancl two stem samples each from plants treated with various amounts of 2,4-D) were carrie(d out simultaneously in a single run. The weight of tissue used in each flask was adjusted to within 20 mlg between samples in the first three experiments and to within 5 mg in the later runs. Unless otherwise indicated, the fresh weight of stem tissues used in each flask was between 1.7 and 1.8 gm.Radiochemicals were purchased fromi Volk Radiochemical Co. and Nuclear Chicago Corp. All labele(d substrates were adjusted to either 1 Ac or 2 uc per mg of glucose prior to administration.
RESULTS AND DISCuSSIONUsing C14 labeled glucose, the effect of 2.4-D on glucose utilization of bean steml tissues has been measured directly. It is assunmed that the oxidation of radioactive carbon atoms from the absorbed glucose which subsequently was recovered in respiratorv C1409 was used to furnish the energy, while the radioactivity found in 80 % ethanol insoluble residue was presumably used in the syntlhesis of cell wall nmaterials.As shown in table I, the percent of absorbed glucose-U-C14 recovered as C1402 had an average value of 5.0 (± 0.4) from six individual runs in control stem tissues. In all cases, the radiochemical yields of respiratory C140.2 hadl greatly increased in 2,4-D treated 405www.plantphysiol.org on May 11, 2018 -Published by Downloaded from