Ultrastructure and Differentiation of Protein-storing Cells in Secondary phloem of Hevea brasiliensis Stem

The ultrastructure and differentiation of the protein-storingcells in secondary phloem of terminal branchlets of Hevea brasiliensisMull. Arg. were studied using electron microscopy. The cellsare parenchyma tissue in the axial system and characterizedby the presence of a large amount of proteinaceous fibrils inthe central vacuole. The fibrils of the protein-storing cellsare straight, about 9 nm in diameter and arranged in a directionroughly parallel to the longitudinal axis of the stem. At theearly differentiation stage of the protein-storing cells, amass of proteinaceous fibrils appears in the cytoplasm, thenis separated from the peripheral cytoplasm by the endomembranesystem derived from endoplasmic reticulum, resulting in theformation of the central vacuole with the fibrils inside asthe vacuolar content The peripheral cytoplasm may continue toproduce proteinaceous fibrils with which the fibrils of thecentral vacuole is supplemented after the protein-storing cellsare formed. Hevea brasiliensis, storage protein, proteinaceous fibrils, vacuole, secondary phloem