Bursts of incorporation into RNA and ribonuclease activities associated with induction of morphogenesis inPharbitis

Uridine-5-³H incorporation into the macromolecules of the apices ofPharbitis nil, Chois, cv. Violet, a species requiring an induction of a single dark period of about 14 hours in order to flower, was measured. Uridine incorporation was greater in plants induced to flower: The two peaks with the maximum rate of incorporation occurred at 14 and 17 hours after the beginning of the dark period. If the dark period was broken by a short illumination, flowering did not occur and uridine incorporation was reduced almost to the control level. RNase activity was higher in the apices of induced plants than in the controls, with a peak activity between the peaks of uridine incorporation, followed by a second increase after the second peak of uridine activity. Methods were devised to extract RNA in the presence of these increased levels of RNase. Fractionation on polyacrylamide gels showed no great differences in the pattern of incorporation during the first period of maximum incorporation. There was greatly increased incorporation into RNA in plants induced to flower. This increase seemed to be the same for rRNA, sRNA, and possibly the relatively non-UV-absorbing (high specific activity) RNA.