Composition and role of tapetal lipid bodies in the biogenesis of the pollen coat of Brassica napus

The composition of the two major lipidic organelles of the tapetum of Brass ica napus L. has been determined. Elaioplasts contained numerous small (0.2 -0.6 mu m) lipid bodies that were largely made up of sterol esters and tria cylglycerols, with monogalactosyldiacylglycerol as the major polar lipid, T his is the first report in any species of the presence of non-cytosolic, st erol ester-rich. lipid bodies. The elaioplast lipid bodies also contained 3 4- and 36-kDa proteins which were shown by N-terminal sequencing to be homo logous to fibrillin and other plastid lipid-associated proteins. Tapetosome s contained mainly polyunsaturated triacylglycerols and associated phosphol ipids plus a diverse class of oleosin-like proteins. The pollen coat, which is derived from tapetosomes and elaioplasts, was largely made up of sterol esters and the C-terminal domains of the oleosin-like proteins, but contai ned virtually no galactolipids, triacylglycerols or plastid lipid-associate d proteins, The sterol compositions of the elaioplast and pollen coat were almost identical, consisting of stigmasterol > campestdienol > campesterol > sitosterol much greater than cholesterol, which is consistent with the ma jority of the pollen coat lipids being derived from elaioplasts. These data demonstrate that there is substantial remodelling of both the lipid and pr otein components of elaioplasts and tapetosomes following their release int o the anther locule from lysed tapetal cells, and that components of both o rganelles contribute to the formation of the lipidic coating of mature poll en grains.