When plants wilt they're soft stems and leaves begin to drop what is going on inside the plant cells that causes the plant to drop like this

The cell membranes begin to come apart when there is insufficient water around the cells. The cytoplasm of the cells becomes more concentrated, which slowly poisons the cells. The cell walls become brittle as they dry out, and some of them collapse. The central vacuoles in the cells lose water and can no longer help support the cells.

The central vacuoles in the cells lose water and can no longer help support the cells