Idioblast Oil Cells of Avocado: Distribution, Isolation, Ultrastructure, Histochemistry, and Biochemistry

Abstract

Procedures for the isolation of highly enriched preparations of specialized oil cells of avocado (Persea americana Mill.) fruit and cleating of plant tissues were applied to an examination of the idioblast oil cells of avocado. These cells are present in all organs examined (leaf, fruit, root, and seed cotyledon) and are dispersed throughout the tissues. Histochemical tests indicate the presence in the oil cells of alkaloids and sesquiterpene hydroperoxides and, possibly, other terpenes. Freeze-fracture electron microscopy of oil cells of the fruit (both in situ and in vitro) indicates that some of the components of the oil contained in these cells undergo a phase transition to a crystalline state at 4 C, while the storage lipid in the mesophyll cells, primarily triacylglycerols, does not. Thin-layer chromatography (TLC) of a lipid extract of the isolated oil cell preparation shows at least six different components with a polarity less than phospholipids but greater than tri- or diacylglycerols. The TLC-detectable composition of the lipid in oil cells remained unchanged during fruit maturation and ripening.