Characterization of prolamellar bodies, from dark‐grown seedlings of Scots pine, containing light‐ and NADPH‐dependent protochlorophyllide oxidoreductase

Abstract

Cotyledons of conifers have a light‐independent pathway for chlorophyll biosynthesis. To investigate whether the prolamellar body of Scots pine (Pinus sylveslris L.) is similar to the better known prolamellar body of wheat, etioplast membrane fractions were isolated from cotyledons of dark‐grown Scots pine. Dark‐grown cotyledons contained both chlorophyll and protochlorophyllide, 158 and 10 nmol (g fresh weight)’respectively, and had a chlorophyll a to b ratio of 4.2. The content of glyco‐ and phospholipids was 7.1 μmol (g fresh weight)1. About 40 mol % of these lipids were the specific plastid lipids – monogalactosyl diacylglycerol. digalactosyl diacylglycerol and sulfoquinovosyl diacylglycerol in the relative amounts 50, 35 and 7 mol %. The mol ratio of monogalactosyl diacylglycerol to digalactosyl diacylglycerol was 1.7. Low temperature fluorescence emission spectra of intact cotyledons and homogenate showed maxima at 633, 657, 686, 696 nm and a broad peak at 725–735 nm. The maxima at 633 and 657 nm represented different forms of protochlorophyllide and the other emission maxima represented chlorophyll protein complexes. The 657 nm form of protochlorophyllide was phototransformable both in vivo and in the isolated membranes. The phototransformable protochlorophyllide was substantially enriched in the prolamellar body fraction.The specific activity of light dependent protochlorophyllide oxidoreductase in the prolamellar body fraction was found to be 2 nmol chlorophyllide formed [(mg protein)−1 min−1]. The molecular weight of the enzyme polypeptide was determined as 38 000 dalton with sodium dodecylsulphate‐polyacrylamide gel electrophoresis.