Respiration of mitochondria isolated from tulip bulbs stored at 5 and 17°C

For the production of good quality flowers, tulip ( Tulipus gesneriana L.) bulbs need a period of low temperature. In cultivar Apeldoom a treatment of 12 weeks at 5 C can be used. In the bulb scales the respiratory metabolism has to adjust to this low temperature. Mitochondria isolated from the bulb scales are able to use succinate. NADH and pyruvate as respiratory substrates. Respiratory characteristics of these mitochondria changed after transfer of the bulbs to 5°C and the adaptation was complete within 2 weeks. Both state 3 respiration and respiratory control increased. Alternative pathway capacity was constitutively present at both 5°C and 17°C: it was low and substrate dependent at both temperatures. During the following weeks of the treatment no significant changes took place. However, when bulbs were transferred to 17°C after storage at 5°C. various responses could be demonstrated. In bulbs only cooled for a short period no readjustment to this higher temperature occurred. In bulbs stored for longer periods the change depended on the duration of the 5°C treatment. The nature of the re-adaptation is discussed