Sprouting rate, change of carbohydrate contents and related enzymes during cold treatment of lily bulblets regenerated in vitro

This study was performed to investigate the effect of low temperature storage on the dormancy of in vitro bulblets of Lilium Oriental hybrid 'Casablanca' and Lilium Asiatic hybrid 'Mona'. All bulblets regenerated in vitro remained dormant, irrespective of cultivar, if they are not subjected to cold treatment. Physiological dormancy was released more rapidly and the highest percentage of sprouting occurred after a 9-week cold treatment at 4 degreesC, as compared with 25 and 10 degreesC. Exposure to low but non-freezing temperatures induced the net breakdown of starch and the accumulation of sucrose and glucose in lily bulblets regenerated in vitro (low temperature sweetening). Bulb sweetening was especially pronounced at 4 C. Analysis of carbohydrate types revealed that sucrose was the dominant soluble carbohydrate in bulblets regenerated in vitro, with glucose and fructose present at significantly lower concentrations. Starch-degrading enzymes alpha- and beta-amylase exhibited higher activities in both cultivars after cold treatment. Varying level of sucrose phosphate synthase, sucrose synthase and invertase activities were also observed after cold treatments. (C) 2002 Published by Elsevier Science B.V.