DNA Multiplication as a Requirement for Expression of Floral Stimulus in Pharbitis nil

Publisher Website
Google Scholar
Abstract
Floral initiation in young seedlings of Pharbitis nil, strain Violet, is inhibited by application of 5-fluorouracil (5- FU) and 5-fluorodeoxyuridine (5- FD) to the plumule before or shortly after a 16 hour inductive dark period. 5- FDU is about 1000 times more effective as an inhibitor of flowering than 5- FU. Labeled 5- FU is translocated from the cotyledons to the plumule, but not in the reverse direction. The inhibitors exert their effect in the plumule, they do not interfere with production of floral stimulus in the cotyledons. The floral stimulus mover from Pharbitis cotyledons to the plumules most rapidly during the 1st 4 hours after a 16 hour dark period. Only precursors of DNA like thymidine, thymidylic acid and deoxyuridine can overcome the flower inhibition by 5- FU and 5- FDU if applied to the plumule before or simultaneously with the inhibitors, indicating that blocking of DNA multiplication is the mechanism by which the antimetabolites suppress flowering. This is further substantiated by the fact that 5- FDU application completely blocks mitotic activity in the apex for 24 to 48 hours. It is concluded that the floral stimulus can express itself in the initiation of floral primordia only in an apex with multiplying DNA.