Vacuolar sorting behaviors of 11S globulins in plant cells.

Plant seed cells amass storage proteins that are synthesized on the endoplasmic reticulumn (ER) and then transported to protein storage vacuoles (PSVs). Many dicotyledonous seeds contain 11S globulin (11S) as a major storage protein. We investigated the accumulation behaviors of pea and pumpkin 11S during seed maturation and compared them with soybean 11S biogenesis (Mori et al., 2004). The accumulation of pea 11S in seeds was very similar to that of soybean 11S at all the development stages we examined, whereas pumpkin 11S condensed in the ER. The determinant of accumulation behavior might be the surface hydrophobicity of 11S. Further, we examined the accumulation of 11Ss in tobacco BY-2 cells to analyze behavior in the same environment. 11Ss expressed in BY2 cells were all observed in precursor form (pro11S). Pro11S with high surface hydrophobicity might be transported to vacuoles in a multivesicular body-mediated pathway when the expression level remains low.