A NEW CLASS OF ARABIDOPSIS MUTANTS WITH REDUCED HEXADECATRIENOIC ACIDFATTY-ACID LEVELS

Chloroplast glycerolipids in a number of higher-plant species, includi ng Arabidopsis thaliana, are synthesized by two distinct pathways term ed the prokaryotic and eukaryotic pathways. The molecules of galactoli pids produced by the prokaryotic pathway contain substantial amounts o f hexadecatrienoic acid fatty acid. Here we describe a new class of mu tants, designated gly1, with reduced levels of hexadecatrienoic acid. Lipid fatty acid profiles indicated that gly1 mutants exhibited a redu ced carbon flux through the prokaryotic pathway that was compensated f or by an increased carbon flux through the eukaryotic pathway. Genetic and biochemical approaches revealed that the gly1 phenotype could not be explained by a deficiency in the enzymes of the prokaryotic pathwa y. The flux of fatty acids into the prokaryotic pathway is sensitive t o changes in glycerol-3-phosphate (G3P) availability, and the chloropl ast G3P pool can be increased by exogenous application of glycerol to leaves. Exogenous glycerol treatment of gly1 plants allowed chemical c omplementation of the mutant phenotype. These results are consistent w ith a mutant lesion affecting the G3P supply within the chloroplast. T he gly1 mutants may therefore help in determining the pathway for synt hesis of chloroplast G3P.