Abstract

Seedlings of larch, pine and spruce were grown in darkness and some of them were later illuminated for 24 or 48 hours. Chloroplast differentiation in cotyledons of these seedlings was investigated by electron microscopy. In the larch the dark-formed chloroplasts have immature lamellar systems with minute grana formed by 2-3 thylakoids. In the pine the diameters of the grana are much larger but they are still formed by only 2-4 thylakoids. Corresponding spruce chloroplasts have advanced larnellar systems with large grana containing up to about 10 thylakoids. Chloroplasts of larch and pine have a few large prolamellar bodies with a more or less narrow spacing of their structural units, while spruce chloroplasts have many small prolamellar bodies with narrow or wide spacing or a combination of both. All three species have large starch grains in their chloroplasts. After 48 hours of illumination the conifer seedlings possess mature chloroplasts with many prominent grana. Prolamellar bodies are only found in a small fraction of the larch chloroplasts. Chloroplast starch grains are common in the spruce, but rare or absent in the other two species.