Studies on growth regulators. I. Improved Avena coleoptile elongation test for auxin.

A modified procedure is presented for the bioassay of auxin using Avena coleoptile segments. The modifications introduced result in a substantial improvement of the commonly used coleoptile elongation tests.The proposed test retains the simplicity of physical requirements and of manipulation characteristic of all elongation tests. The main feature of the proposed test is that it permits the measurement of the elongation of coleoptile segments as being directly proportional to the concentration rather than to the logarithm of the concentration of indoleacetic acid. With an accuracy and a range comparable to those of the standard Avena curvature test, the proposed bioassay overcomes the limitations for the quantitative assessment of auxin inherent in other coleoptile elongation tests. An additional advantage is provided by the present procedure: two 5 mm segments from each coleoptile can be utilized thus doubling the number of assays hitherto possible with a given number of coleoptiles.