Certain Mitotic Effects of Kinetin, Gibberellic Acid, Maleic Hydrazide, and Indoleacetic Acid in Onion Roots

Growing, intact, adventitious roots from the bulbs of Allium cepa were treated with 1 ppm and 10 ppm solutions of kinetin, gibberellic acid, maleic hydrazide, and indoleacetic acid, and with paired combinations of these. The effect on the rate of mitosis was studied by counting the mitotic figures present in the distal 5 mm. of the root tip in serial longitudinal sections. Roots treated with kinetin alone or in any combination showed marked inhibition of mitosis. There was initial inhibition followed by an after-effect of stimulation of mitosis in roots treated with gibberellic acid, with indoleacetic acid, or with a combination of these. Maleic hydrazide did not reverse the action of any of the auxin-like substances tested, but the after-effect of stimulation was not seen when it was present. Roots treated with maleic hydrazide contained many cells in which the chromosomes showed aberrations including fragmentation and changes which gave the chromosomes a beaded appearance