RNA metabolism in apices of Pharbitis nil daring floral induction

Abstract

RNA metabolism was studied in apices of Pharbitis nil during and after floral induction. In continuous light ³H-uridine accumulated in RNA at a constant rate over an 18 hr period. In darkness, however, the rate of accumulation of label into RNA was constant until the 10th hour at which time a rapid burst of accumulation occurred, peaking at the 14th hour of darkness and followed by a net loss of label. The RNA involved in this burst is probably mRNA due to its size and poly(A) content. This phenomenon does not seem to be associated with floral induction, since the site of perception is the apex, and it also occurs under conditions where floral initiation is inhibited by a brief light interruption of the dark period. Immediately after floral induction by a 16-hr dark period the rate of RNA synthesis was suppressed about 14%. This suppression lasts for about 12 hr and was followed by a twofold increase in the rate of RNA synthesis, compared to non-induced apices, at 64 hr after the beginning of the inductive dark period. These post-induction changes were found to occur in all RNA fractions.