The effects of cold temperature on the activity of α-amylase and on carbohydrate composition were investigated in the bulb scales of tulip plants (Tulipa gesneriana). Some bulbs were stored at 15℃ for 3 weeks from August 30, 1991, and subsequently at 2℃ for 8 weeks. Another group of control bulbs was stored at room temperature during the same period. Both groups of bulbs were planted in a green house at about 20℃ from October 30, 1991. The α-amylase activity in cold-stored bulb scales increased gradually during the cold-storage period and the degradation of starch and the concomitant accumulation of sucrose and fructans were observed. After planting, the α-amylase activity of cold-treated bulbs increased dramatically and the degradation of starch was accelerated. On the other hand, the α-amylase activity also increased in control bulbs, although starch degradation did not occur. After separated by isoelectric focusing gel electrophoresis, α-amylase isozyme patterns were compared between cold-treated and control bulbs. The same two a-amylase isozymes occurred in bulbs receiving both treatments during the cold storage period. Starch was stained with iodine solution and the distribution of starch in the scales was observed microscopically. In control bulb scales, no starch was observed in the few cell layers immediately below the epidermis, but starch granules were filled in the inner cells. In cold-treated bulb scales, some inner cells lost their starch granules. By in situ observation of α-amylase activity by starch-film method and by the separate measurement of α-amylase activity in the outer and inner cells of scales, it was suggested that outer cells without starch contained higher activity of α-amylase both in control and cold-treated bulbs. The activity was also detected in the inner cells of cold-treated bulbs, but not in the inner cells of the control bulbs. Based on the results obtained, it was suggested that low temperature treatment induces α-amylase activity in inner cells which store a large amount of starch. Although control bulb scales also had high α-amylase activity, it was restricted to a few layers of outer cells and did not occur in the inner cells.
