Annual Changes in Responsiveness of Shoot Tip Cultures to Cytokinin in Japanese Persimmon

Abstract

To determine the best season for shoot tip culture of Japanese persimmon, shoot tips were cultured monthly from February 1987 to January 1988 in 1/2N-MS basal medium, Murashige and Skoog′s medium containing half strength nitrogen, with zeatin. No shoot growth was observed in the medium without zeatin. In any month of the year, the shoot growth was enhanced by 10^-5M zeatin. The activity of shoot tips in shoot elongation increased from late April to late June, and shoot length after six weeks of culture was maximum on 22 June. Thereafter, activity decreased until late October and then remained constant until early April. These changes in shoot growth in vitro coincided with the changes of depth of internal dormancy. Leaf number was high in 10^-5M zeatin only on 30 May and 22 June. From principal component analysis using four growth characteristics for the medium with 10^-5M zeatin, the first principal component score in June was the largest of the year. Shoot tip growth in June had, therefore, better shoot elongation, leaf differentiation, callus formation and mortality rate, so the appropriate season for shoot tip culture of Japanese persimmon was considered to be June.