Enzymatic catabolism of ascorbate in florets of harvested broccoli during senescence

Broccoli (Brassica oleracea L. var. italica) florets senesced rapidly after harvest at ambient room temperatures. Whole plants of broccoli were harves ted in the field and brought to the laboratory, then the stem was excised f rom the root. Ethylene production in the first cross-sectional layer (2 mm thick) initially increased markedly from a trace amount at 0 hr to a peak a t 12 hr, then decreased gradually. The rate of ethylene production in flore ts increased gradually after harvest to reach a maximum at 24 hr. A high am ount of ascorbate in florets at harvest, just after separation from the ste m, rapidly declined to a low level during senescence. However, in the stem tissue including the cut surface, the ascorbate level which was much less t han that of florets, remained almost unchanged during the experimental peri od. Ascorbate peroxidase (APX), which may be responsible for the first step in ascorbate oxidation retained high activity in broccoli florets after ha rvest, then decreased slightly during senescence. These results suggest tha t some additional factors (components) besides high APX activity could be i nvolved in the rapid breakdown of ascorbate.