Direct interaction between glyoxysomes and lipid bodies in cotyledons of the Arabidopsis thaliana ped1 mutant

During germination and subsequent growth of fatty seeds, higher plants obtain energy from the glyconcogenic pathway in which fatty acids are converted to succinate in glyoxysomes, which contain enzymes for fatty acid beta -oxidation and the glyoxylate cycle. The Arabidopsis thaliana peril gene encodes a 3-ketoacyl-CoA thiolase (EC 2.3.1.16) involved in fatty acid beta -oxidation. The peril mutant shows normal germination and seedling growth under white light. However, etiolated cotyledons of the peril mutant grow poorly in the dark and have small cotyledons. To elucidate the mechanisms of lipid degradation during germination in the peril mutant, we examined the morphology Of the peril mutant. The glyoxysomes in etiolated cotyledons of the peril mutant appeared abnormal, having tubular structures that contained many vesicles. Electron microscopic analysis revealed that the tubular structures in glyoxysomes are derived from invagination of the glyoxysomal membrane. By immunoelectron microscopic analysis, acyl-CoA synthetase (EC 6.2.1.3), which was located on the membrane of glyoxysomes in wildtype plants, was located on the membranes of the tubular structures in the glyoxysomes in the ped1 mutant. These invagination sites were always in contact with lipid bodies. The tubular structure had many vesicles containing substances with the same electron density as those in the lipid bodies. From these results, we propose a model in which there is a direct mechanism of transporting lipids from the lipid bodies to glyoxysomes during fatty acid beta -oxidation.