Enzymatic catabolism of ascorbate in florets of harvested broccoli [Brassica oleracea italica] during senescence
2001
Nishikawa, F. (Shizuoka Univ. (Japan). Faculty of Agriculture) | Kato, M. | Kamo, T. | Wang, R. | Hyodo, H. | Ikoma, Y. | Sugiura, M. | Yano, M.
Broccoli (Brassica oleracea L. var. italica) florets senesced rapidly after harvest at ambient room temperatures. Whole plants of broccoli were harvested in the field and brought to the laboratory, then the stem was excised from 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 at 12 hr, then decreased gradually. The rate of ethylene production in florets increased gradually after harvest to reach a maximum at 24 hr. A high amount of ascorbate in florets at harvest, just after separation from the stem, rapidly declined to a low level during senescence. However, in the stem tissue including the cut surface, the ascorbate level which was much less than that of florets, remained almost unchanged during the experimental period. Ascorbate peroxidase (APX), which may be responsible for the first step in ascorbate oxidation retained high activity in broccoli florets after harvest, then decreased slightly during senescence. These results suggest that some additional factors (components) besides high APX activity could be involved in the rapid breakdown of ascorbate.
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