Plant cell vacuoles serve the same vital storage functions for nutrients, water and wastes as those in animal cells but are much larger because they also provide structural stiffness in combination with the plant's cell walls. This is why water-starved plants droop; their cells have essentially deflated. If a living but wilted plant once again receives sufficient water, it regains its former stiffness as the vacuoles refill.
Because of the size of the vacuoles in plant cells, often occupying most of the space in each cell, they are used for many of the functions for which animal cells use other organelles. For instance, plant vacuoles tend to be acidic and contain enzymes that act like those in lysosomes in animal cells. They also contain many compounds important in cell defense. Sometimes, they are even used to trap pathogens and toxic substances. Their importance in plant cells is much greater than in animal cells.
Plant vacuoles have variety beyond the large, water-filled central vacuoles, however. Many fruits and seeds have protein-storing vacuoles, for instance. Some plants even use vacuoles for rapid defensive movements. While plant cell vacuoles differ greatly from animal cell vacuoles, they have several similarities to those in algae and even in yeasts.