"Until now, our hypothesis that there was movement of the Short-Root protein between cells was based on a discordance between where the protein acted and where it was originally made, which was in a different cell," said Benfey. "However, very little was known about how or whether this movement was controlled."
The scientists theorized that the protein moved from cell to cell through channels called plasmodesmata that exist between plant cells. Once it reaches its target cell, the protein migrates to the cell's nucleus -- the site of the cell's genetic material -- where it exerts its effects. Similar channels, called "nanotubes," have only recently been discovered in animal cells.
The question, said Benfey, was whether the movement of the Short-Root protein was simple random diffusion between the two cells' cytoplasm -- their liquid interior -- or whether transport occurred via a controlled process.
To follow the transport of the protein, Benfey and his colleagues used a tracer molecule that enabled them to pinpoint the Short-Root protein in living root cells. These studies indicated that in the cells from which the protein moves, it exists in the cytoplasm not associated with any molecular complex. However, the tracer did not reveal that the protein was moving from one cell to another.
The researchers also found that they could disrupt normal movement of the protein by genetically mutating its gene at only a single point. This discovery implied that the protein required a transport machinery to move from one cell to the other. The mutation presumably disrupted the protein's ability to dock with that machinery.
"So, we believe we've shown that there is an active process that recognizes signals, and it's not just a matter of the protein being cytoplasmically localize
Contact: Dennis Meredith