ASPARAGINE SYNTHETASE GENE-EXPRESSION INCREASES AS SUCROSE DECLINES IN BROCCOLI AFTER HARVEST

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