To find out the formation time of stone cell, drought stress, isolated from water by plastic house, was inflicted on pear trees at 30 days before full bloom, full bloom stage, 30 days after full bloom and 60 days after full bloom during 30 days, respectively. Adhesiveness, gumminess, cohesiveness and chewiness increased suddenly in fruits contained stone cell more then 28.0mg/g in flesh and hardness was higher in pear fruit with higher stone cells, but the changes of the springiness as contents of the stone cells showed no difference. By optical microscope, stone cell observed first from 14 days after full bloom. The adjacent cells to stone cell was first showed spherical type on initial forming stage but showed radial form at 90 days after full bloom. The shape of stone cell inspected by SEM was like a cluster and its size was various. By using TEM, components of stone cell, such as nucleus and vacuole, and secondary cell wall thickening were observed, so it could consider that the stone cell is living thing. The largest amount of stone cell clusters existed beneath fruit skin. The stone cell in flesh enlarged by drought stress compared to control, and then stone cell per areas was the largest at 30 days after full bloom. Therefore, it seems that the drought stress became a cause of inducing stone cell. The stone cell was decreased by the application of calcium chloride 0.5 %, on 30 days after full bloom. Also, fruit firmness was increased compared to control on harvest time. Calcium chloride application showed a possibility for the inhibition of stone cell formation
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