Anyone tell me what effect colchicine has on cells in metaphase and why?

Colchicine inhibits the formation of mitotic spindle, which effectively shuts down mitosis and cell division.

 

During metaphase, mitotic spindle is used to move the chromosomes onto the metaphase plate. If colchicine is present, the spindle doesn't form, and the chromosomes cannot line up in the center of the cell, so the cell never ends up dividing.

To be more specific it causes the depolimerization of microtubles. (mitotic spindels being microtubles.)

Well... you're right. Cholchicine binds to the tubulin dimers, which prevents them from polymerizing. Actually, it also shuts down cell movement because cilia/flagella are composed of microtubules (which is why cholchicine is used to treat gout, since it shuts down movement and division of white blood cells)

Thanks very much! thats helped a lot:D