Pigment and acyl lipid composition of photosystem I and II vesicles and of photosynthetic mutants in barley

Abstract

The pigment and acyl lipid composition of photochemically active stroma lamellae and inside-out photosystem II vesicles have been investigated. Mechanical disruption followed by phase partitioning in an aqueous two phase system resulted in a clean separation of the photosystems. A qualitative and quantitative determination of the pigment content was achieved using reversed-phase high performance liquid chromatography. A single chromatographic separation provided adequate resolution of neoxanthin, violaxanthin, lutein, chlorophyllb, chlorophylla, and β-carotene and was completed in 22 min. For each molecule ofP700, the stroma lamellae contained 166 molecules of chlorophylla, 14 molecules of chlorophyllb, 0 molecules of neoxanthin, 3 molecules of violaxanthin, 7 molecules of lutein, and 13 molecules of β-carotene. For each molecule ofP680 the photosystem II vesicles contained 250 molecules of chlorophylla, 100 molecules of chlorophyllb, 7 molecules of neoxanthin, 7 molecules of violaxanthin, 22 molecules of lutein, and 4 molecules of β-carotene. The pigment content of three photosynthetic mutantschlorina-f2, viridis-zb 63 andviridis-zd 69 was determined. On a chlorophyll basis, these mutants generally showed a reduced carotenoid content, except thatchlorina-f2 had an increased level of β-carotene andviridis-zd 69 an unaltered level of lutein. The acyl lipid composition of stroma lamellae, photosystem II vesicles and lamellar systems was also determined. Although the photochemical activities of the stroma lamellae and photosystem II vesicles were enriched compared to the parent lamellar system, more than 50% of the acyl lipids in the subchloroplastic membranes were degraded or severely modified resulting in a drastically reduced content of monogalactosyldiglyceride and digalactosyldiglyceride in the stroma lamellae and photosystem II vesicles. Due to the lipolytic degradation the level of saturation in the galactolipids was higher in stroma lamellae and photosystem II vesicles compared with the lamellar system. Stroma lamellae do not contain the light-harvesting chlorophylla/b-protein, but were enriched in phosphatidylglycerol and trans-3-hexadecenoic acid.