Carotenoid Transformations in the Chloroplast Envelope

Abstract

The envelope of the spinach chloroplast is a yellow membrane system with a unique carotenoid composition. Envelopes prepared from dark-treated leaves had a violaxanthin content up to 3.5 times the lutein plus zeaxanthin content, whereas in chloroplast envelopes from illuminated leaves this ratio was only 0.75. Light-catalyzed changes in violaxanthin content also occurred in the thylakoid fraction.The role of this reversible light-catalyzed de-epoxidation of violaxanthin in the function of the envelope of the chloroplast is discussed.In a recent paper by Douce et al. (1) it was reported that violaxanthin constituted a greater proportion of the carotenoids of the chloroplast envelope than of the thylakoids of ordinarily prepared spinach chloroplasts. There is now considerable evidence (2) that the conversion of violaxanthin to zeaxanthin occurs when isolated spinach chloroplasts are illuminated. The biochemical mechanism of this conversion has been studied (3, 4), but its physiological significance remains obscure (2).In this paper we report the recognition of a light-dependent conversion of violaxanthin to zeaxanthin in the envelope of spinach chloroplasts. MATERIALS AND METHODSSpinach obtained from local markets was stored briefly at 40. Whole leaves were washed, placed in water at 20°, and exposed either to white light (1.2 X 108 ergs/cm2 per sec) or to darkness for 2 hr. Chloroplasts were prepared according to the "aqueous" method of Walker (5). The purification of intact chloroplasts-(class I) was carried out by a modification of the method of Leech (6). The chloroplast envelope, thylakoid, and stroma were prepared and characterized as described (1). The membrane fractions isolated by discontinuous sucrose gradient centrifugation were concentrated as pellets by centrifugation.Protein content was determined by the method of Lowry et al. (7)

Molecular aspects of plastid envelope biochemistry

“…3). In all envelope membranes, violaxanthin is the major carotenoid whereas thylakoids are richer in /&carotene [87]. The xanthophyll/P-carotene ratio is about 6 in chloroplast envelope membranes, but only 3 in thylakoids.…”

The Maize Phytoene Synthase Gene Family: Overlapping Roles for Carotenogenesis in Endosperm, Photomorphogenesis, and Thermal Stress Tolerance

“…Early studies provided evidence that an envelopelocalized carotenoid biosynthetic pathway might also exist in chloroplasts. Chloroplast envelope membranes were shown to contain a unique carotenoid profile compared to thylakoid membranes (Jeffrey et al, 1974;Siefermann-Harms et al, 1978); chloroplast envelope membrane extracts also exhibited enzyme activity for conversion of zeaxanthin to violaxanthin (Costes et al, 1979). More recent reports have localized PSY and other pathway enzymes to thylakoid membranes in chloroplasts (Linden et al, 1993;Bonk et al, 1997;Welsch et al, 2000).…”

Modifications of Etioplasts in Cotyledons during Prolonged Dark Growth of Sugar Beet Seedlings (Identification of Etiolation-Related Plastidial Aminopeptidase Activities)

“…SDS-PAGE malysis of proteins was carried out in a Mighty Small I1 (Hoefer, San Francisco, CA) electrophoresis unit with gradient ,gels of 9 to 15% acrylamide in the presence of 0.1% (w/v) SDS, essentially as described by O'Farrell (1975). Carotertoids were determined as described by Jeffrey et al (1974). Total Chl was extracted and measured as described previously (El Amrani et al, 1994).…”