CHARACTERIZATION OF SEED OIL BODIES AND THEIR SURFACE OLEOSIN ISOFORMS FROM RICE EMBRYOS

Plant seeds store triacylglycerols in discrete organelles called oil b odies, An oil body stores a matrix of triacylglycerols surrounded by p hospholipids and alkaline proteins termed oleosins. Oil bodies in rice seeds ape present in embryos and aleurone layers, They do not coalesc e in crowded environments, as observed on electron microscopy. The det ected isoelectric point of purified rice oil bodies is pH 6.2, This im plies that rice oil bodies possess a negatively charged surface at neu tral PH The suspension of rice oil bodies in pH 6.5 buffer induces agg regation, Presumably, the negatively charged surface causes electrosta tic repulsion Chat maintains rice oil bodies as discrete organelles, R ice oil bodies lose their integrity on trypsin treatment, Undoubtedly, oleosins play an important role in the stability of oil bodies, There are two oleosin isoforms in rice oil bodies, Antibodies raised agains t these two homologous isoforms do not cross-recognize each other. Bot h isoforms are restricted to oil bodies, as detected on immuno-assayin g. Partial amino acid sequences of these two isoforms were obtained, a nd compared with the deduced sequences of two maize and two rice oleos in genes, The comparison confirmed that the two major proteins in rice oil bodies ape the two oleosin isoforms.