科研之友
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摘要
Broccoli (Brassica oleracea var. italica) kept at ambient temperatures after harvest senesce rapidly and sucrose levels decrease. However, if exogenous sucrose is supplied back to the plant, senescence symptoms can be delayed for up to 48 h. Acid invertase enzyme activity increases after harvest in broccoli stored at 20 degreesC and an investigation was undertaken to see if this enzyme has a role in the senescence process. Soluble acid invertase enzyme was extracted from fresh broccoli (0 h) and after 96 h of storage. There were two peaks of invertase activity, one at pH 5-5.5 and the other at pH 8. Broccoli stored in water and sucrose had reduced levels of acid invertase enzyme activity after 48 h compared to those stored dry. Similarly, broccoli kept in a controlled atmosphere (CA) of 10% CO(2) and 5% O(2) senesced at a slower rate and had significantly less acid invertase enzyme activity than air controls after 48 h. Two broccoli acid invertase cDNAs (BoINV1 and BoINV2) were isolated and these had 85 and 90% identity at the nucleotide and amino acid level. RNA blot analysis with BoINV1 and BoINV2 showed that transcripts of approximately 2.3 kb accumulated during senescence of the broccoli florets. The accumulation pattern was similar for both acid invertases but the level of accumulation was greater for the BoINV2 encoded transcript. The accumulation of these transcripts was delayed by water, sucrose and CA treatments compared to the controls. Southern analysis experiments demonstrated that the two cloned acid invertases are part of a small gene family. These findings suggest that acid invertase may be one of the key enzymes responsible for the reduction in sucrose levels that accompanies the rapid deterioration of harvested broccoli.
- 出版日期2003-4
