RNA Synthesis in the Apex ofSinapis albain Transition to Flowering

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Abstract
RNA synthesis in the 1.5 mm apex during floral evocation of Sinapis alba (a long-day plant) was measured using a double-labelling technique to compare precursor incorporation in evoked and vegetative apices, followed by analysis by gel electrophoresis and oligo(dT)-cellulose chromatography. In plants induced to flower by exposure to a single long day, higher levels of RNA synthesis showed a two-phase pattern, the first increase starting very early in evocation, from 10 h after the start of the long day. This early extra synthesis is of rRNA, and then also sRNA.2 Subsequently higher levels of RNA synthesis, especially rRNA and 5S RNA, are shown from 36 h. At no time was such additional synthesis of the RNA fraction retained on oligo(dT)-cellulose detected. The experiment was repeated with plants subjected to a single displaced short day, a treatment which also induces flowering, and similar higher RNA synthesis found in evoked apices. These results were compared with those obtained in two non-inductive treatments which result in some features of floral evocation: a single short day at high intensity light, and a single treatment with benzyladenine. Neither gave rise to additional RNA synthesis, and thus the observed high levels of synthesis of rRNA and sRNA seem to be associated with other features of floral evocation.