Regulation of the Onset of Dormancy in Tubers of Begonia evansiana

The concept of dormancy as a condition of repressed genetic information was first proposed by Tuan and Bonner (7). from experiments which showed an increased template activity of chromatin isolated from potato tutbers upon emergence from dormancy. The repressioni concept has since received general acceptance (1). It would seem possible that the entry into the dorm-iant state mlav be a conisequence of synthetic evenits programmiiiied in the genome. If this is true, the inistructions for the onset of dormancy nmay require transcription into RNA and translatioii into proteins. Our experiments with Begonia reveal that the entry into dormancy can be prevented by a wide ranige of inhibitors of nucleic acid and protein synthesis. Tubers of Begonia evansiano Andr. are especially convenient for this type of experiment since they are induced to become dormant by exposure to relatively brief periods of low temperature and red light (5). Aerial tubers were obtained from plants grown in the greenhouse under short photoperiods (9 hr). Tubers were harvested at about the half-growvn condition (stage 5 to 7 of Esashi, 4) at whiclh stage they are not dormant. The standard treatmenit uised to induce dormancy vas to place the tubers on iuioist filter paper in Petri dishes for 20 days in a chamiber at 150 under a red light (60 w tungsten lamp behind ruby glass filter transmitting above 560 mju), after which germinability was determined over an additional 50 days in a growth chamber (1000 ft-c, 16 hr photoperiod, 250). The tubers (25 per treatment) were supplied with the various inhibitors in the solution used to moisten the filter paper. After the 20 days of dormancy induction, the tubers were rinsed and placed on paper moistened with water. The effectiveness of the dormancy inducing treatments is illustrated in Fig. 1, showing the progress