Effects of Certain Acid Growth-Regulating Substances and Their Corresponding Aldehydes on the Growth of Roots

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Abstract
A micro-assay method for growth substances based on effects on root elongation of Artemisia absinthium and 11 other spp. or vars. was established. Root growth of 10 seedlings on a 0.1-ml. agar square was studied. The responses to 3-indole acetaldehyde (IAAld), 1-naphthalene acetaldehyde (NAAld), 3-indoleacetic acid (IAAcid), and 1-naphthaleneacetic acid (NAAcid) were observed and measured for 24-hr. periods over a range of concns. from 10-6 to 105 ug./l. These growth substances were added to the agar by the ether-dropping method. All 4 compounds inhibited root elongation at certain concns., more so for 4-hr than 14-hr. periods. Those concns. bringing about 50% inhibition of root elongation over 24-hr. periods corresponded Closely to those bringing about 15[degree] curvature in the Avena test for all 4 substances. The acetaldehydes were approx. 1/10 as effective as the acids. NAAld was 1/10 as effective as IAAld. NAAcid was less effective than IAAcid at high concns., more effective at low concns. Stimulation of root elongation by growth substances at low concns. occurred over 24-hr. periods, and was statistically established for IAAcid at 10-1 [mu]g./l. and for IAAld at 10-3.2 [mu]g./l. Juice obtained from Artemesia roots had the capacity to convert NAAld to NAAcid. A further, unexplained loss of NAAld occurs during this conversion; NAAcid is stable in root juice. All 4 substances at relatively high concns. brought about morphological changes: virtually no elongation, subterminal swellings, and limited root-hair production. Root elongation appeared more sensitive to growth substances than did root-hair production.