Inhibition of Photoperiodic Induction by 5-Fluorouracil

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Abstract
Photoperiodic induction of Xanthium pennsylvanicum, the cocklebur, is inhibited by application of 5-fluorouracil. A given amount of 5-fluorouracil is in general more effective in inhibiting photoperiodic induction when applied to the buds than when applied to the leaves, the known perceptor organ in photoperiodic induction. 5-Fluorouracil is fully effective in inhibiting photoperiodic induction only if applied during the inductive dark period. This is true even of 5-fluorouracil application to the apical bud. It appears, therefore, that something essential to induction takes place in the bud during the exposure of the leaf to an inductive dark period. 5-Fluorouracil inhibition of photoperiodic induction is reversed by applying orotic acid. The hypothesis is suggested that photoperiodic induction involves nucleotide metabolism, possibly nucleic acid synthesis.