Shoot primordia of annual Haplopappus gracilis (2n=4) propagating vegetatively in vitro provided a new possibility for freeze preservation. The method of freeze preservation was as follows. Subcultured shoot primordia were precultured in an MS medium supplemented with 5% DMSO for 3 days. They were cooled at a velocity of -0.5°C/min down to -40°C in a programming freezer, and then stored in liquid nitrogen immediately. The frozen shoot primordia were thawed quickly in a water bath at 37°C, and recultured. The recovered shoot primordia were highly stable in the chromosome number and karyotype, which were the same as in the original plant and in the control shoot primordia without the freezing treatment. In comparison with a method using shoot tips, the above method is advantageous of being possible to store a large number of pieces of shoot primordia more easily, and also to mass-propagate plantlets clonally.
The Genetics Society of Japan