NOVEL MUTATIONS AFFECTING LEAF STEARATE CONTENT AND PLANT SIZE IN ARABIDOPSIS

The fab2-1 mutant of Arabidopsis is an extreme dwarf as a direct resul t of an increase in the levels of stearate (18:0) in membrane lipids. We isolated a series of lines in which second-site suppressor mutation s partly alleviate the dwarf phenotype. In all four of the suppressor lines examined, restoration of more normal morphology is accompanied b y decreases in leaf 18:0 content. Three of the isolated suppressors su ppress the high stearate phenotype in both leaves and seeds. The effec ts of one of the suppressors, TW2-1, is limited to the leaves. A secon d allele at the fab2 locus, fab2-2, was also identified and plants hom ozygous for this allele where intermediate in both plant size and 18:0 content between wild-type Arabidopsis and fab2-1 mutants. The alleles at fab2 and the suppressor mutations provided a total of nine genotyp es which were analyzed to demonstrate a clear-cut relationship between leaf 18:0 content (0.7-19.6% of total leaf fatty acids) and reduction s in plant size (24-4 mm). These results illustrate the utility of sup pressor analysis for addressing problems in biochemistry and plant bio logy. They also indicate that the genetic control of plant lipid compo sition is more complex than previously appreciated.