Starch content of freeze-dried anthers and α-amylase activity of their extracts as criteria that dry-stored bulbs (Tulipa gesneriana, L.) cultivar ‘Apeldoorn’ have been exposed to 5°C

Starch and sucrose were estimated selectively in freeze-dried anthers from tulip bulbs pre-cooled at 5°C for 12 weeks and from a control batch maintained at 17°C. α-Amylase activity in anther extracts was also estimated. Based on data from our own trials (1981, 1982 and 1983) and from 18 batches from typical bulb-producing regions in The Netherlands (year 1983), sucrose was discarded as indicator. The following tentative criteria are proposed for detecting whether dry bulbs cultivar ‘Apeldoorn’ have been exposed to 5°C: starch content of freeze-dried anthers should exceed 10% and specific activity of α-amylase should be below 0.16 (arbitrary unit per mg protein). These criteria are not indicative of the duration of the 5°C period.