Submitted to: Phytochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2006
Publication Date: 9/1/2006
Citation: Li, L., Lu, S., Cosman, K., Earle, E., Garvin, D.F., O'Neill, J. 2006. B-carotene accumulation induced by the cauliflower or gene is not due to an increased capacity of biosynthesis. Phytochemistry. 67:1177-1184. Interpretive Summary: Carotenoids play an important role in human nutrition and health. They act as antioxidants in reducing the incidence of certain diseases and serve as the primary source of dietary pro-vitamin A. Vitamin A deficiency is a global problem. It is estimated that more than 250 million children worldwide are at risk. As humans are unable to synthesize vitamin A de novo from endogenous isoprenoid precursors, all vitamin A in our foods can ultimately be traced back to a carotenoid origin. To ultimately increase carotenoid content in plant foods, we need to understand how the carotenoid synthesis and accumulation are regulated in plants. A cauliflower high beta-carotene orange (Or) gene mutation provides a good model to study these regulatory mechanisms. As part of this research, in this paper, we report on a biochemical study of the effect of the Or gene mutation on metabolic flux through the carotenoid biosynthetic pathway. Our results showed that the Or mutation does not increase metabolic flux through the carotenoid pathway, suggesting that other mechanisms are involved in the regulation of high-beta carotene accumulation.
Technical Abstract: The cauliflower (Brassica oleracea L. var. botrytis) Or gene is a rare carotenoid gene mutation that confers a high level of B-carotene accumulation in various tissues of the plant, turning them orange. To investigate the biochemical basis of the Or-induced carotenogenesis, we examined the carotenoid biosynthesis by evaluating phytoene accumulation in the presence of norflurazon, an effective inhibitor of phytoene desaturase. Calli were generated from young seedlings of wild type and the Or mutant plants. While the calli derived from wild type seedlings showed a pale green color, the calli derived from Or seedlings exhibited intense orange color, showing the Or mutant phenotype. Concomitantly, the Or calli accumulated significantly more carotenoids than the wild type controls. Upon treatment with norflurazon, both the wild type and Or calli synthesized significant amounts of phytoene. The phytoene was accumulated at comparable levels and no major difference in the carotenogenic gene expression was observed between the wild type and Or calli. These results suggested that the Or-induced B-carotene accumulation does not result from an increased capacity of carotenoid biosynthesis.