Effects of 5-fluorouracil on photoperiodic induction and nucleic acid metabolism of xanthium.

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Abstract
The application of 5-fluorouracil (5-FU) to Xanthium buds prior to photoperiodic induction reduced the development of the floral primordia. Plants given 2-3 photoinductive dark cycles with 5-FU applied at the beginning of each cycle, showed less inhibition of the floral development than when only 1 cycle was given. While development of the floral primordia was reduced by 5-FU it appears that only high levels (10-2 [image]) applied to plants given 1 photoinductive dark cycle effectively stopped flowering. Therefore, it is concluded that 5-FU is not a specific inhibitor of flowering in Xanthium plants. Estimation of the amounts of various fractions of RNA as revealed by fractionation on methylated albumin-kieselguhr columns indicated that nucleic acids from buds of noninduced and induced plants were essentially identical. Using the same technique, it was found that 5-FU inhibited DNA and ribosomal RNA to a much greater extent than messenger RNA. Messenger RNA appeared fairly resistant to the inhibitory action of 5-FU. Labeling excised tissue in solution preferentially promoted the synthesis of messenger RNA as compared to intact labeled tissue. Excising tissue from the plant influenced nucleic-acid metabolism in a manner similar to depriving bacteria of nutrients required for optimum growth (step-down cultures).
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