Control of Plastidic Glycolipid Synthesis and Its Relation to Chlorophyll Formation <sup><a href="#fn1" rid="fn1" class=" fn">1</a></sup>
Abstract
Mechanisms restricting the accumulation of chloroplast glycolipids in achlorophyllous etiolated or heat-treated 70S ribosome-deficient rye leaves (Secale cereale L. cv “Halo”) and thereby coupling glycolipid formation to the availability of chlorophyll, were investigated by comparing [C]acetate incorporation by leaf segments of different age and subsequent chase experiments. In green leaves [C]acetate incorporation into all major glycerolipids increased with age. In etiolated leaves glycerolipid synthesis developed much more slowly. In light-grown, heat-bleached leaves [C]acetate incorporation into glycolipids was high at the youngest stage but declined with age. In green leaves [C]acetate incorporation into unesterified fatty acids and all major glycerolipids was immediately and strongly diminished after application of an inhibitor of chlorophyll synthesis, 4,6-dioxoheptanoic acid. The turnover of glyco- or phospholipids did not differ markedly in green, etiolated, or heat-bleached leaves. The total capacity of isolated ribosome-deficient plastids for fatty acid synthesis was not much lower than that of isolated chloroplasts. However, the main products synthesized from [C]acetate by chloroplasts were unesterified fatty acids, phosphatidic acid, and diacylglycerol, while those produced by ribosome-deficient plastids were unesterified fatty acids, phosphatidic acid, and phosphatidylglycerol. Isolated heat-bleached plastids exhibited a strikingly lower galactosyltransferase activity than chloroplasts, suggesting that this reaction was rate-limiting, and lacked phosphatidate phosphatase activity.
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