ALTERED BODY MORPHOLOGY IS CAUSED BY INCREASED STEARATE LEVELS IN A MUTANT OF ARABIDOPSIS

A mutant of Arabidopsis thaliana, fab2 in which a profound developmental phenotype, miniature growth, is caused by an increase in the level of the membrane fatty acid, stearate has been characterized. Miniature growth in faba results from changes in cell expansion and maturation processes. Leaf anatomy of fab2 is characterized by cell-specific changes in expansion growth, by a lack of differentiation in the cells of the leaf blade, and by the absence of air spaces. Leaves of fab2 lack the basipetal gradient in cellular development which is ubiquitous in higher plants. These cellular changes occur without distorting the chronology of development, or destroying the biological integrity of the organism. A second site suppressor mutation, shs, substantially restores both normal fatty acid composition and normal body size, causally linking the two phenotypes. Growth of the fab2 mutant at high temperature substantially corrects the miniature phenotype without altering the fatty acid composition, suggesting a role for membrane structure in the production of the aberrant morphology.