Farmacognosia

Disponível somente no TrabalhosFeitos
  • Páginas : 23 (5635 palavras )
  • Download(s) : 0
  • Publicado : 18 de abril de 2013
Ler documento completo
Amostra do texto
PHYTOCHEMISTRY Phytochemistry 67 (2006) 1177–1184 www.elsevier.com/locate/phytochem

b-Carotene accumulation induced by the cauliflower Or gene is not due to an increased capacity of biosynthesis
Li Li
a

a,b,*

, Shan Lu a,c, Kelly M. Cosman a, Elizabeth D. Earle b, David F. Garvin d, Jennifer O’Neill a

d

USDA-ARS, Plant, Soil and Nutrition Laboratory, Cornell University, Ithaca, NY14853, USA b Department of Plant Breeding and Genetics, Cornell University, Ithaca, NY 14853, USA c Department of Plant Biology, Cornell University, Ithaca, NY 14853, USA USDA-ARS, Plant Science Research Unit, University of Minnesota, St. Paul, MN 55108, USA Received 1 December 2005; received in revised form 2 March 2006

Abstract The cauliflower (Brassica oleracea L. var. botrytis) Or gene is arare 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 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 seedlingsof wild type and 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 significantamounts of phytoene. The phytoene accumulated at comparable levels and no major differences in carotenogenic gene expression were observed between the wild type and Or calli. These results suggest that Orinduced b-carotene accumulation does not result from an increased capacity of carotenoid biosynthesis. Ó 2006 Elsevier Ltd. All rights reserved.
Keywords: Brassica oleracea var. botrytis;Cauliflower; Brassicaceae; Or gene mutation; Carotenoids; Norflurazon

1. Introduction Carotenoids are a diverse group of pigments widely distributed in nature. They fulfill many functions in plants such as in light harvesting and photoprotection (Demmig-Adams and Adams, 1996; Frank and Cogdell, 1996); in providing precursors for the biosynthesis of the plant hormone, abscisic acid (ABA) (Schwartz et al.,1997), and for production of the volatile fruit flavor/aroma (Simkin et al., 2004). In addition, carotenoids play an important role in human nutrition and health as the primary dietary source of pro-vitamin A (Combs, 1998) and in reducing

*

Corresponding author. Tel.: +1 607 255 5708; fax: +1 607 255 1132. E-mail address: ll37@cornell.edu (L. Li).

the incidence of certain diseases(Giovannucci, 1999; Krinsky et al., 2003). In plants, carotenoids are synthesized de novo within plastids (Fig. 1). The first committed step in carotenoid biosynthesis is condensation of two molecules of geranylgeranyl pyrophosphate (1) to produce phytoene (2). A series of desaturations and isomerizations converts phytoene (2) to lycopene (4). The latter is cyclized to yield a- and b-carotene (5) and (6).Subsequent oxygenation of these carotenes via addition of hydroxyl, epoxy or keto groups results in formation of xanthophylls, including lutein (7) from a-carotene (5), and zeaxanthin (8), violaxanthin and neoxanthin from b-carotene (6) (Cunningham and Gantt, 1998; Hirschberg, 2001; Fraser and Bramley, 2004). Lutein (7), b-carotene (6), violaxanthin and neoxanthin are the most abundant carotenoids ingreen tissue of many higher

0031-9422/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.phytochem.2006.05.013

1178

L. Li et al. / Phytochemistry 67 (2006) 1177–1184

GGPP 1
2x norflurazon 9 PSY PDS

phytoene 2 ζ-carotene 3
ZDS LCYe LCYb CHYe CHYb CRTISO

lycopene 4
LCYb

α-carotene 5 β-carotene 6
CHYb

lutein 7

zeaxanthin 8

Fig. 1. An...
tracking img