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Unformatted text preview: Cytokinins Named because of their discovered role in cell division (cytokinesis), the cytokinins have a molecular structure similar to adenine. Naturally occurring zeatin , isolated first from corn ( Zea mays) , is the most active of the cytokinins. Cytokinins are found in sites of active cell division in plantsfor example, in root tips, seeds, fruits, and leaves. They are transported in the xylem and work in the presence of auxin to promote cell division. Differing cytokinin:auxin ratios change the nature of organogenesis. If kinetin is high and auxin low, shoots are formed; if kinetin is low and auxin high, roots are formed. Lateral bud development, which is retarded by auxin, is promoted by cytokinins. Cytokinins also delay the senescence of leaves and promote the expansion of cotyledons. Gibberellins The gibberellins are widespread throughout the plant kingdom, and more than 75 have been...
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- Fall '08