Phyllotaxis in Xanthium Shoots Altered by Gibberellic Acid

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Science  10 Jun 1977:
Vol. 196, Issue 4295, pp. 1201-1203
DOI: 10.1126/science.196.4295.1201


Gibberellic acid treatment of vegetative Xanthium shoots induced a change in phyllotaxis and almost doubled the rate of leaf production. Phyllotaxis in control plants displayed a 2,3 contact parastichy pattern; that of the treated plants could be approximated with a 3,5 pattern. Thus, the Xanthium apex switched to a new mode of growth and a higher order of phyllotactic leaf arrangement not seen in untreated plants. It may be inferred from these experiments that gibberellic acid plays a role in determining the site of leaf initiation.