[Studies on the uptake of naphthalene-1-acetic acid and its aspartic acid conjugate into wheat coleoptile tissue].

The uptake into wheat coleoptile tissue of C-14 radioactivity from naphthalene-1-acetyl-aspartic acid-C-14 (NAAS) compared with that from naphthalene-1-acetic acid-C-14 (NES) is as low as 1:10. The data give strong evidence for an active uptake of NES and even NAAS. A comparison of the NES uptake with the growth response within the first 3 hours indicates that the optimal concentration of auxin for maximal growth rate is about 2 mμMol/hour/g of fresh weight. NAAS acts as an auxin only after hydrolysis to NES. Considering the fact that the tissues show no growth response to NAAS during the first hours of incubation even though the C-14 uptake from this substance is as much as one tenth of that from NES, the hydrolysis of NAAS to NES must take place inside the cells. Chromatographic studies of wheat coleoptile segments incubated in NAAS-C-14 confirm this conclusion.