CHARACTERISTICS OF PROTEIN-STORING CELLS ASSOCIATED WITH A 67 KDA PROTEIN IN HEVEA-BRASILIENSIS

The protein-storing cells (PSCs) in Hevea brasiliensis were studied by using light-and electron-microscopy and SDS-PAGE. The cells were foun d in stem and root where secondary phloem was developed. They are a sp ecial kind of phloem parenchyma cell which accumulate in their central vacuoles large amounts of protein, fibril-like under an electron micr oscope, and have few plastids with very small starch grains. Their dis tribution is strictly restricted to the secondary phloem axial system where they exactly sequestered in functional phloem or slightly over i t. A 67 kDa protein was always found in the tissues where the PSCs wer e observed. During the first seasonal growth flush, the 67 kDa protein in the terminal branchlet exhibits marked quantitative fluctuation wh ich is consistent with the change of the vacuole protein inclusion of the PSCs in the branchlet. These facts suggested that the 67 kDa prote in might be the major part of the vacuole protein of the PSCs. Conside ring the differences between the PSCs in Hevea and the PSCs in the oth er trees studied, we define two types of PSCs: Hevea-type, which are t he cells specialized for protein storage and Populus-type, which are o rdinary parenchyma cells accumulating protein and starch.