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The auxin-like properties of potassium naphthenates and their effect on indole-3-acetic acid biosynthesis and degradation Loh, John Wai-Choong


The auxin-like properties of potassium naphthenates (KNap), and the effect of these compounds on indoleacetic acid (IAA) biosynthesis and degradation were examined. Chapter I. The auxin-like properties of KNap. Cucumber seeds were treated with 1000 ppm KNap and a significant (at the 0.05 level) inhibition of root growth (91%) , compared with control seedlings was obtained. The effects of KNap and indolebutyric acid on the initiation of roots by stem cuttings of Phaseolus vulgaris L. were examined. The treatments with 10 and 100 ppm of both compounds significantly stimulated root initiation. Root initiation of azalea stem cuttings was significantly augmented by 10, 100, and 1000 ppm KNap. The elongation of dark-grown Alaska pea stem segments was stimulated by 1.0 ppm KNap (279% over the control). Surprisingly, this stimulation did not differ significantly from that caused by 0.1 ppm IAA (339% over the control). KNap at 100 and 1000 ppm, applied to the distal end of debladed petioles, did not affect abscission. The times required for 50% abscission of petioles treated with 10 and 1000 ppm cyclohexanecarboxylic acid were significantly greater than that for abscission of control petioles, but not from that required by petioles treated with 100 ppm naphthaleneacetic acid. Chapter II. The effect of KNap on IAA biosynthesis and degradation. When the seeds of Phaseolus vulgaris L. were soaked for 12 hours in a solution of 100 ppm KNap immediately prior to sowing, there was a significant increase (140% over control plants) in the content of IAA in the apical 5-8 cm of the stems of 14-day-old plants. The immersion of the root systems of 13-day-old dark-grown bean plants in a solution of 100 ppm KNap for 24 hours resulted in a significant stimulation (4% over the control) of the activity of the IAA oxidase system. The evidence presented is interpreted as supporting the view that KNap has some auxin-like properties. The validity of this interpretation is discussed.

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