Organelles of plant cells, with variable structure and function depending on the cell type.

Plastids are for example responsible for photosynthesis in leaf cells (green chloroplasts), and for the storage of starch in the cells of storage organs (amyloplasts).

Plastids contain the genes for some of their proteins, and the enzymatic equipment to use these genes. This observation indicates that the organelles have evolved by endosymbiosis from formerly independent, photosynthetic bacteria.