Journal of Lipid Research, Vol. 9, 513-524, July 1968
Copyright © 1968 by Lipid Research, Inc.

Lipid biosynthesis in chloroplast mutants of barley

Lars-Ak°e Appelqvist , John E. Boynton , Knud W. Henningsen , P. K. Stumpf , and Diter Von Wettstein

Department of Biochemistry and Biophysics, Department of Genetics, University of California, Davis, California 95616, and Institute of Genetics, University of Copenhagen, Copenhagen, Denmark

The capacity of leaf slices from light-grown seedlings of wild type barley and 10 xantha mutants at six different gene loci to incorporate acetate-¹⁴C into various lipids has been investigated. The fatty acid composition of the leaf lipids in these lethal mutants was similar to that of the wild type, but the fatty acid labeling pattern in the individual lipid classes can be drastically altered by these mutations, which affect chloroplast differentiation. A genetic block in chlorophyll synthesis, caused by mutations in the xan-f locus, leads to a repression of the formation of chloroplast membranes and of acetate incorporation into phospho-, sulfo-, and galacto-lipids (the acetate being preferentially channeled into a lipid fraction containing steroids and free fatty acids). Two leucine "auxotrophs" at different loci, which in the absence of leucine in the growth medium produce giant grana and accumulate some chlorophyll, differed considerably in the amount of labeling of their polar lipids during incubation.

Leaves of xan-a¹¹, containing plastids with little chlorophyll, highly disorganized membrane systems, and large bodies with osmiophilic deposits, were nonetheless equal to wild type in their capacity to incorporate acetate-¹⁴C into phospho-, sulfo-, and galacto-lipids. The mutants at the xan-m locus have plastids with undispersed prolamellar bodies and osmiophilic packages of grana-like membranes associations. Leaf slices of these mutants synthesized considerably more linolenic acid-¹⁴C, which was incorporated into monogalactosyl diglycerides, than did slices of the wild type. This led to a labeling pattern of the fatty acids in the monogalactolipids which was remarkably similar to their endogenous fatty acid composition.

Supplementary key words barley • xantha mutants • chloroplast structure • acetate incorporation • lipid biosynthesis • monogalactosyl diglyceride • digalactosyl diglyceride • steroids • radio-gas chromatography • linolenic acid

Submitted on February 1, 1968
Accepted on March 26, 1968

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