Decarboxylation and transport of auxin in segments of sunflower and cabbage roots

Summary

The movement of ¹⁴C from indole-3-acetic acid (IAA) ¹⁴C has been examined in 5 mm root segments of dark-grown seedlings of Helianthus annuus and Brassica oleracea. Contaminants from distilled water, phosphate buffer and the razor-blade cutter increase the decarboxylation of IAA-¹⁴C, and cutting of root segments results in an activation of IAA-destroying enzymes at the cut surfaces. When these sources of errors were eliminated the following was shown: a) Both in sunflower and cabbage there is a slight acropetal flux of ¹⁴C through the root segments into the agar receiver blocks. The amount of ¹⁴C found in the receiver blocks increases with the lenght of the transport period. b) When the root segments, after the transport period, are cut in two equal parts and these assayed separately, the amounts of ¹⁴C in the two parts indicate a greater acropetal than basipetal transport. c) The total radioactivity of the receiver blocks is in part due to IAA-¹⁴C and in part to ¹⁴CO₂, the latter being a result of enzymatic destruction of auxin. d) Addition of ferulic acid, an inhibitor of IAA oxidases, to the receiver blocks markedly inhibits the decarboxylation of IAA-¹⁴C and thus increases the amount transported. This effect is more pronounced after a 20 hr than after a 6 hr transport period.