A Comparative Study of the Changes in Root Growth, Induced by Coumarin, Auxin, Ethylene, Kinetin and Gibberellic Acid

The effect of coumarin, IAA, ethylene, kinetin and gibberellic acid on roots of maize and wheat was investigated. Sterile attached and detached roots and isolated elongation zones were used. In some experiments a semi-sterile procedure was followed. The effects of the different regulators separately or in various combinations together with coumarin were studied on the root growth with regard to division, elongation and swelling of the cells. The ethylene production in isolated elongation zones was measured after treatment with coumarin, IAA, PCIB, kinetin, colchicine and dinitrophenol. The results show the following: 1) Each substance produces a specific morphologic pattern. 2) Changes in polarity were demonstrated for auxin-induced swelling in cell divisions and cell expansion and for coumarin-induced swelling in cell divisions. Other cell expansion in swollen parts was due to cylindric cells increasing in width while retaining their cylindric form. 3) Coumarin-induced inhibition could not be counteracted by IAA, PCIB, carbon dioxide, kinetin, gibberellic acid or Cycocel. 4) The ethylene production in isolated elongation zones increases noticeably after kinetin treatment, less strongly after auxin treatment and least after coumarin treatment. The production of ethylene does not seem to be correlated with the morphogenetic effect of the different substances. 5) The isolated elongation zones reacted to a) IAA and kinetin with an increase in length in some cases and b) gibberellic acid with a reduction of their width. 6) The inhibitory effect of coumarin on the growth in length of the elongation zones was diminished by kinetin. The swelling produced by coumarin in these zones was reduced by gibberellic acid. The effects just mentioned of kinetin and gibberellic acid were considered as indirect ones. - From the present findings it was concluded that concomitant effects of auxin, ethylene, cytokinins and gibberellins are not obligatory for coumarin to exert its morphogenetic effects on root growth. In discussing the results some pitfalls in studies of growth reactions after application of hormones to roots containing meristem were emphasized.