Combinations of plant growth regulators, darkness treatments, and the order of expanding leaves for explants were evaluated for optimizing in vitro shoot regeneration rate of 'Whangkeumbae' pear. In a MS medium, supplemented with 8.88 μ M 6-benzylaminopurine (BA) and 0.49 μM indole-3-butyric acid (IBA), green foci were observed on the surface of the callus 8 days after culture initiation. Some adventitious buds were later induced from those green foci, resulting in the appearance of normal shoots. In a medium containing 22.20 μM BA, the surface of the callus became compact and greenish, and many adventitious buds were formed over the entire area of the callus surface. When comparing BA concentration via histological observation, the section which had been treated with 22.20 μM BA exhibited closer cell aggregation than those with 8.88 μM BA. The darkness treatment enhanced the formation of adventitious shoots for up to 3 weeks. The youngest two expanding leaves, proximal to the shoot apex, were proved to be the most regenerative, and yielded the highest shoot number per regenerating leaf. A fourth strength MS medium, which was supplemented with 0.54 μ M NAA, yielded good quality plantlets, with regard to root number and root length.

ABSTRACT
 Ⅰ. Introduction
 Ⅱ. Materials and Methods
  2.1 Preparation of explants
  2.2 General factors affecting the regenerationprocess
 Ⅲ. Results and Discussion
  3.1 General factors affecting the regenerationprocess
 Literature cited

• Gung-Pyo Lee(Dept. of Applied Plant Science, Chung-Ang Univ.) 교신저자