Drug that binds to tubulin molecules of plant cells and prevents the cells from assembling spindle microtubules would most likely cause the resulting plants or plant cells to have: .

More than two complete sets of the chromosomes (polyploidy).

Explanation:

Assembly of spindle microtubules assist the chromosomes to arrange in the equator of the cell during metaphase. This is followed by the splitting of centromere and segregation of sister chromatids towards the opposite poles of the cell to ensure equal distribution of chromosomes among the daughter cells.

Any drug that prevents the assembly of the spindle apparatus would not allow the alignment of the chromosomes in the cell's equator. This would prevent the anaphasic segregation of daughter chromosomes to the opposite poles.  

Some of the resulting daughter cells are most likely to have more than two sets of chromosomes.