Dormancy and sprouting in onion (Allium cepa L.) bulbs. I. Changes in carbohydrate metabolism

Dormancy and sprouting were studied in two onion cultivars with a clear period of dormancy using a large number of replicates, and single-bulb sampling. Dormancy was evaluated on the basis of sprout leaf elongation. Changes in respiratory activity, ATP and ADP content, sucrose synthase activity, dry matter (DM) content, and the contents of glucose, fructose, sucrose, fructan, and water-soluble carbohydrates (WSC), were determined in sprout leaves, stem plate and bulb scales at weekly intervals. During dormancy, and before sprouting, changes in DM contents and various WSC in different bulb parts suggested mobilisation and translocation of WSC. After a period of dormancy, the sucrose synthase activity and respiratory activity in the centre of the bulb increased, concomitant with initial sprout growth. The demonstrated separation between dormancy and the sprouting period in these cultivars should provide a good starting point for comprehensive studies on dormancy regulation in onion bulbs.