Auxin biosynthesis and metabolism in isolated roots of Zea mays

The synthesis and metabolism of indole-3-acetic acid (IAA) was investigated in isolated roots of corn, Zea mays L. Roots were cultured aseptically in media supplemented with either ¹⁴C-tryptophan or ¹⁴C-IAA. Exogenously supplied IAA is rapidly and completely metabolized by root tissues. The main site in the root for the synthesis of IAA is in the apex. Removal of either the root cap or the quiescent center, or the root cap and the quiescent center from the apex has no effect on the IAA-synthesizing ability of the apex. Subdividing the terminal 2.1 cm of the root into various segments and culturing them separately stimulates IAA synthesis in these isolated root tissues. Roots in culture maintain relatively constant IAA levels, reflecting the precise controls of the level of this hormone.