CHANGES IN RESPIRATORY CHARACTERISTICS AND ETHYLENE PRODUCTION IN TULIP BULBS AFTER COLD TREATMENT
Mitochondrial characteristics of transferred bulbs cooled for a long period before transfer differed from those only cooled for a short period. After a long 5°C pretreatment succinate state 3 and RC values showed a decline, in contrast with bulbs only cooled for a short period. Alternative pathway capacity did not show such a relation with the length of the period of cooling.
Parallel to these measurements of mitochondrial respiration the ethylene production of intact bulbs was studied. Ethylene production by tulip bulbs was very low (1–35 nl C2H4 [h]-1 [kg FW]-1). For all 4 series we found a gradual rise in ethylene production during cold storage. At the end of the season more ethylene was produced in control bulbs stored at 17°C than in 5°C bulbs.
To check the effect of the length of the cooling period on flowering, bulbs from all series were planted in a glasshouse after various periods of cooling at 5°C. Within one series, flowerstalks of 11, 12 and 13 weeks 5°C cooled bulbs were comparable in length but this length gradually decreased in the season. In the last series 9 and 16 weeks 5°C bulbs had shorter flowerstalks than 11–13 weeks cooled bulbs. This was in contrast with the first two series where lengths from 9–16 weeks cooled bulbs showed no significant differences.