Asparagine synthetase gene expression increases as sucrose declines in broccoli after harvest

Abstract

Broccoli (Brassica oleracea L.) floral tissues rapidly differentiate and grow before harvest and then senesce rapidly after harvest. The factors regulating this rapid postharvest senescence are currently under investigation. We show that within 6 h of harvest sucrose concentration in florets declines by c. 50%, and between 24 and 72 h asparagine levels increase more than 7‐fold. This increase in asparagine parallels an earlier increase in asparagine synthetase (AS) gene expression in florets. Northern analyses show that AS transcript abundance increases from 2 to 24 h after harvest, and then declines. AS transcript abundance also increases in harvested leaves as they turn yellow, although to a level lower than that seen in florets. In other plant systems, including asparagus, increases in AS gene expression occur as a result of a decline in sucrose status. We note the considerable similarities between broccoli and asparagus postharvest physiology and discuss our results for broccoli AS in terms of possible regulation by sucrose status.

Key words:

• asparagine
• asparagine synthetase
• broccoli
• postharvest
• sucrose