I can't seem to find the answer to this. Not even Wikipedia could help- it mentioned bacteria and fungi that have cellulases but not plants. Using my own reasoning, I would think that
- On the one hand it is better if plant cells do not have cellulases so that they do not break down the cell wall. Although maybe it doesn't matter because the cellulases would not reach the cell wall without being actively transported out of the plasma membrane.
- Perhaps it might be useful for plants to have cellulase. I don't know if plants have any sort of immune system like humans, but plants also get bacterial and parasitic infections in their cells. Maybe plants should have some mechanism to destroy an unhealthy cell? In that case, the destroying cells would need to use cellulase, would they not?