JXB Advance Access originally published online on September 25, 2003
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Journal of Experimental Botany, Vol. 54, No. 392, pp. 2439-2448,
November 1, 2003
© 2003 Oxford University Press
Ascorbate metabolism in harvested broccoli
Received 7 July 2003; Accepted 21 July 2003
1 The United Graduate School of Agricultural Science, Gifu University (Shizuoka University), Yanagido, Gifu, 501-1193 Japan
2 Department of Biological Sciences, Faculty of Agriculture, Shizuoka University, 836 Ohya, Shizuoka, 422-8529 Japan
3 Department of Citriculture, National Institute of Fruit Tree Science, Okitsu, Shimizu, 424-0292 Japan
* To whom correspondence should be addressed. Fax: +81 54 2373028. E-mail: w1611012{at}ipc.shizuoka.ac.jp
The ascorbate content declined rapidly in broccoli (Brassica oleracea L. var. italica) florets, but not in the stem tissue, during post-harvest senescence. Ascorbate peroxidase (APX), ascorbate oxidase (AO), L-galactono-1,4-lactone dehydrogenase (GLDH), monodehydroascorbate reductase (MDAR), dehydroascorbate reductase (DHAR), and glutathione reductase (GR) were investigated in gene expression after harvest in both florets and the stem tissue of broccoli. Cytosolic gene expressions (BO-APX 1, BO-APX 2, BO-AO, BO-MDAR 2, and BO-GR) were stimulated actively in broccoli florets after harvest. By contrast, it was observed that mRNA levels of chloroplastic APX, BO-sAPX and BO-tbAPX, had decreased by 12 h after harvest in broccoli florets, suggesting that the active oxygen species (AOS) scavenging system in chloroplasts was largely abolished in florets during the early hours of the post-harvest period. In addition, gene expressions in GLDH and other chloroplastic enzymes such as BO-MDAR 1 and BO-DHAR decreased rapidly within 24 h after harvest. Ethylene treatment had no effect on the ascorbate level and the expression of all genes investigated. The expressions of BO-GLDH and chloroplastic genes (BO-sAPX, BO-tbAPX, BO-MDAR 1, and BO-DHAR) mRNA were suppressed by treatment with methyl jasmonate (MJ) and abscisic acid (ABA) and were accompanied by the acceleration of ascorbate degradation. These data suggest that ascorbate metabolism tends to be inactivated in chloroplasts by transcriptional regulation, but not in the cytosol, when ascorbate decreases under stress conditions.
Key words: Active oxygen species, ascorbate, Brassica oleracea, gene expression, harvest.
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