Ribonucleic Acid Synthesis in the Bud Essential Component of Floral Induction in Xanthium

Abstract

Photoperiodic induction of Xanthium pennsylvanicum is inhibited by the application of 5-fluorouracil to the apical bud during a 16-hour inductive dark period. Experiments with labeled 5-FU show that the inhibitor is not translocated from bud to leaf during the 16-hour dark period, although it is translocated from leaf to bud .5-FU not only depres-ses synthesis of both RNA and DNA in the apical bud of Xanthium, but also is itself incorporated into RNA. Such incorporation as well as inhibition of photoperiodic induction is reversed by the application of orotic acid. 5-FU is most active in inhibition of photoperiodic induction if applied at the beginning of an inductive dark period. Reversal of such inhibition by orotic acid is possible only if the latter is applied simultaneous ly with the 5-FU. If orotic acid is applied as little as 8 hours after application of 5-FU reversal of inhibition is incomplete or nil. 5-Fluoro-. deoxyuridine (5-FDU) specifically inhibits multiplication of DNA in the apical buds of Xanthium. Such inhibition is reversed by application of of thymidine. It is shown that suppression of DNA multiplication during the inductive dark period, followed by reversal of such inhibition at the end of dark period does not adversely affect photoperiodic induction. It is concluded that RNA synthesis is the process essential to photoperiodic induction which is inhibited by the presence of 5-fluorouracil in the bud of Xanthium during an otherwise inductive dark period. Multiplication of DNA during this same period appears to not be essential.