Abstract
1. A study was carried out to investigate changes of respiratory mechanism of onion bulbs in relation to the dormancy, from last stage of bulb development to sprouting period of Senshu-nakate (Yellow Danvers) onions.
2. The amount of gaseous metabolism of onion bulbs decreased rapidly in the last stage of bulb development to reach too a minimum rate, and remained approximately constant at the minimum rate for a considerable period after the harvest, and commenced to rise gradually toward the sprouting period. This tendency was observed similarly both in the disk part (bottom part), which is considered to have important role on the physiology of onion bulbs, as well as in the whole bulb.
3. In the disk part of onion bulb, it seems that sugars might be decomposed completely through EMBDEN-MEYERHOF's pathway followed by TCA cycle. The unity value of respiratory quotient was observed throughout the experimental period.
4. Dehydrogenases, connected with TCA cycle in the disk tissue of the onion bulb, were found to have very low activity during the rest period, and then activated sharply in the middle or late of August, which period roughly corresponds to that of respiratory rise.
5. It was also observed that the addition of uncoupler of oxidative phosphorylation (DNP) resulted to introduce relatively little effect on the respiration of disk tissue during the rest period, but it caused remarkable increase of oxygen uptake at the critical period mentioned above, suggesting that the qualitative change of respiratory mechanism had occurred.
6. There was no influence of moisture condition on rooting and/or sprouting of onion bulbs for a considerable period after the harvest, notwithstanding the bulbs began rooting rapidly in the middle of August when they were placed on the moist sand.
7. These experimental results suggest that the accurate rest period of “Senshu-nakate” onion bulbs under the ordinary storage conditions would have been terminated by the middle or end of August, two months or more earlier than the visual sprouting period.
8. The variance in respiratory rate due to the. difference of variety was also measured. The respiration in the disk tissue of onion bulbs which belong to early-ripe varieties was lower than that of the late varieties at the last stage of bulb development, however, the reverse tendency was found from the rest period through pre-sprouting period. It seems, therefore, that early-ripe onions should go into the rest earlier than the onions of late varieties, but, they possibly lose more amount of substrates than the latter during the storage. Greater energy generation in early-ripe onions at pre-sprouting period might be favorable to induce earlier sprouting.
