Leaf explants of Allium sativum L. (2n = 16) were cultured in vitro on nutrient media with different hormonal composition. Karyological changes were analyzed both by chromosome counting and cytophotometry. The media containing 2,4-dichlorophenoxyacetic acid (2,4-D) alone or in combination with kinetin (KIN) and β-indoleacetic acid (IAA) were the only to induce callus formation. Callus induction was accompanied by an increase in the ploidy level. The least karyological heterogeneity was observed with callus on medium with equimolar concentrations of 2,4-D and KIN while the highest variability was recorded on medium with 2,4-D alone. Polyploid cells originated from diploid cells rather than from polyploid ones pre-existing in the explant. Restitution mitoses were most probably the main mechanism of origin of polyploid cells.

Institute of Experimental Botany Sokolovská 6 CS 772 00 Olomouc Czechoslovakia

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Synthetic auxin herbicide 2,4-D and its influence on a model BY-2 suspension