Formation of Polar Lipids and Isoprenoid Compounds in Heat-Treated 70S Ribosome-Deficient Rye Leaves

The chloroplast-specific glycolipids monogalactosyldiacylglycerol, digalactosyldiacylglycerol, sulfoquinovosyldiacylglycerol and the prenylquinones α-tocopherol, plastoquinone-9 and phylloquinone were formed in the 70S ribosome-deficient leaf tissue of rye seedlings grown at a non-permissive temperature of 32°C. In light 32°-grown 70S ribosome-deficient leaves were chlorotic. Etiolated 32°-grown leaves contained about 50% of the protochlorophyll(ide) content of control leaves from permissive growth conditions (22°C). As in chloroplasts, monogalactosyldiacylglycerol and digalactosyldiacylglycerol were the predominating polar lipids in isolated bleached ribosome-deficient plastids. Sulfoquinovosyldiacylglycerol and the phospholipids phosphatidylcholine, phosphatidylglycerol and phosphatidylinositol were also present. The 32°-grown 70S ribosome-deficient leaves contained the same molecular species of monogalactosyldiacylglycerol and digalactosyldiacylglycerol as 22°-grown control leaves. As under permissive conditions linoleic and linolenic acid were the prevailing fatty acids of the galactolipids from 70S ribosome-deficient leaves. All enzymes of the biosynthesis of protochlorophyll(ide) and of the chloroplast glycolipids and prenylquinones must be synthesized on cytoplasmic 80S ribosomes. In accord with the reduction of the thylakoid system the ratio of monogalactosyldiacylglycerol to digalactosyldiacylglycerol was lower in 70S ribosome-deficient than in normal green leaves. In etiolated leaves grown at either 32°C or 22°C the amounts of the glycolipids and prenylquinones did not differ markedly. However, in light the glycolipid and prenylquinone contents remained almost as low in the bleached 70S ribosome-deficient leaves as in darkness, while several-fold increases accompanied greening of normal leaves in light. The data suggest that the light-mediated increase of glycolipids and prenylquinones depends on the availability of chlorophyll. The contents of steroidal saponins in oat leaves were slightly higher in light than in darkness and showed no specific relationship to the presence of etioplasts. They did not notably differ in 22°- or 32°-grown leaves.