Differential presence of oleosins in oleogenic seed and mesocarp tissues in olive (Olea europaea) and avocado (Persea americana)

Olive drupes accumulate triacylglycerol (TAG) in the fleshy mesocarp of the fruit and also in the endosperm and embryo tissue of their seeds. Ultrastructural analysis has shown that, whereas the TAG in the seed tissues is stored in small, relatively regular oil bodies with diameters in the region of 0.5–2.0 μm, it is present in large, irregular oil bodies of 10–20 μm in the mesocarp. The fatty acid profiles of the TAG in oil bodies isolated from seed and mesocarp tissues are very similar, but oil bodies from these tissues differ dramatically in their protein content. Oil bodies from olive seed endosperm and embryo tissues contain about 10% (w/w) protein, whereas no significant protein was detected in oil bodies from mesocarp tissue of olive or avocado. Major polypeptides of 22 kDa and 50 kDa were purified from olive seed oil bodies and antibodies were raised against them. The 22-kDa oil-body protein was demonstrated to be an oleosin, based on its exclusive localisation on the surface of oil bodies of mature seed tissues, as shown by immunogold electron microscopy. It is concluded that oleosins, such as the 22-kDa polypeptide in olive, are present in the long-term storage oil bodies from the embryo and endosperm tissues of the seed and are absent from oil bodies of the mesocarp.