Large changes in the population of cell wall proteins accompany the shift to cell elongation

The expression patterns of cell wall proteins in mung bean hypocotyls both before and during cell elongation have been investigated. The results suggest two clear conclusions. First, it is shown that there is a large population of cell wall-specific proteins (at least 20 abundant ones and perhaps as many as 250 minor ones) detectable on 2-D gels. Second, of these proteins more than half differ markedly in their levels of expression between non-elongating or elongating cells in the hypocotyl tissue. Some are up-regulated while others are down-regulated. Various controls ensure that cytosolic contamination is minimal and that the changes seen represent real switches in cell wall protein expression. The results indicate that this approach provides a sound strategy for the future identification and characterization of cell wall proteins specifically associated with cell elongation.