1979 Volume 48 Issue 1 Pages 61-66
In the previous paper (6) it was reported that when hypocotyl segments of lettuce seedlings were precultured for a week on the medium including 2, 4-D and kinetin (KIN), adventitious buds were formed successfully in the hypocotyl segments. The present paper deals with the effects of various concentrations of 2, 4-D and KIN added to the White's basal medium singly and in combination on the formation of adventitious buds. The previously defined terms, i.e., ‘initial’ media and ‘transfer’ media, are conveniently used also in this paper. The results obtained are as follows:
1) For the induction of adventitious buds, favorable concentrations of 2, 4-D and KIN added to the initial medium were estimated to be 0.1 to 1.0mg/l and 0.5 to 5.0mg/l, respectively.
2) For the bud formation, it seemed requisite to supply both 2, 4-D and KIN during the entire course of preculture. In fact, if 2, 4-D was singly added to the initial medium during the first 4 days of the preculture, the formation of adventitious buds was completely inhibited even up to the completion of subsequent subculture. This inhibitory effect caused by 2, 4-D, however, was alleviated by subjecting the cultures to continuous illumination. When 2, 4-D was added to the initial medium during the first 2 days of the preculture, its inhibitory effect was alleviated also by extension of the subsequent subculture period, about 10 days, along with the use of culture media supplemented with both 2, 4-D and KIN.
3) By subculturing on the transfer medium supplemented singly with 0.05 to 0.5mg/l KIN, sufficient numbers of adventitious buds were formed, though addition of 2, 4-D to the transfer medium exerted some inhibitory effects on the bud formation in every combination with different KIN concentrations.
4) KIN exhibited the most pronounced inductive effect on the formation of adventitious buds by its supplementation during the period from the first to the second week of the subsequent subculture.
5) From the results obtained, it is suggested that the processes of the adventitious bud formation in the lettuce hypocotyl segments cultured in vitro consist of three distinctive phases, i.e., (1) bud induction that is brought about when precultured for a week on the initial medium including both 2, 4-D and KIN, (2) bud initiation that occurs during the transition period prior to shifting the cultures to the transfer medium containing KIN alone, and (3) bud development that has been completed on the transfer medium.
