A MUTANT OF ARABIDOPSIS WITH INCREASED LEVELS OF STEARIC-ACID

A mutation at the fab2 locus of Arabidopsis caused increased levels of stearate in leaves. The increase in leaf stearate in fab2 varied deve lopmentally, and the largest increase occurred in young leaves, where stearate accounted for almost 20% of total leaf fatty acids. The fatty acid composition of leaf lipids isolated from the fab2 mutant showed increased stearate in all the major glycerolipids of both the chloropl ast and extrachloroplast membranes. Although the stearate content was increased, the fab2 mutant still contained abundant amounts of 18:1, 1 8:2, and 18:3 fatty acids. These results are consistent with the expec tations for a mutation partially affecting the action of the stromal s tearoyl-acyl carrier protein desaturase. Positional analysis indicated that the extra 18:0 is excluded with high specificity from the sn-2 p osition of both chloroplast and extrachloroplast glycerolipids. Althou gh stearate content was increased in all the major leaf membrane lipid s, the amount of increase varied considerably among the different lipi ds, from a high of 25% of fatty acids in phosphatidylcholine to a low of 2.9% of fatty acids in monogalactosyldiacylglycerol.