title: Glycerolipid-fatty-acid desaturase deficiencies in chloroplasts from fruits of Capsicum annuum L.
abstract: Chloroplasts from fruits and leaves of Capsicum annuum cv. 'Bell Tower' were purified on sucrose gradients, and the lipids were separated by column and thin-layer chromatography. The glycerolipids mono- and digalactosyldiacylglycerol (MGDG, DGDG), sulfoquinovosyldiacylglycerol (SQDG), and phosphatidylglycerol (PG) were quantified, and the fatty-acid composition at the 1 and 2 positions of the glycerol moiety (sn-1 and sn-2) was determined after hydrolysis with position-specific lipases. In fruit chloroplasts, Δ (3)-trans hexadecenoate (trans-3-16∶1) was absent and replaced by palmitate (16∶0) at sn-2 of PG, and Δ (7,10,13)-hexadecatrienoate (16∶3) at sn-2 of MGDG was greatly reduced and largely replaced by linoleate (18∶2). The ratio of 18∶2 to linolenate (18∶3) was consistently greater in glycerolipids from fruit compared with leaf chloroplasts. The lower percentage of C-16 fatty acids at sn-2 indicated that "prokaryotic" molecular species were reduced by ≤15% in DGDG, ∼40% in SQDG, and ∼90% in MGDG, in fruit compared with leaf chloroplasts. The MGDG∶DGDG ratios in fruit and leaf chloroplasts were 1.2∶1 and 2.2∶1, respectively. Taken together, the data indicate that chloroplasts in Capsicum fruit are deficient in three desaturases: those that convert 1) 16∶0 to Δ (3)-trans-16∶1 at sn-2 of PG, 2) 16∶0 to Δ (7)-cis-16∶1 at sn-2 of MGDG, and 3) 18∶2 to 18∶3 at both sn-1 and sn-2 of various chloroplast glycerolipids.
authors.affiliation: U.S. Department of Agriculture, Agricultural Research Service, Horticultural Crops Quality Laboratory, Beltsville Agricultural Research Center-West, 20705-2350, Beltsville, MD, USA.
authors.forename: B D
authors.initials: BD
authors.lastname: Whitaker