They are separated from the hyaloplasm by a double plastid membrane, made up of a smooth outer plastid membrane, a 60 Å chamber, and an inner plastid membrane (both 75 Å) that has ramifications towards the interior of the chloroplast called lamellae, where some flat discoidal saccules (thylakoids) that group together to form pimples. The membrane of the lamellae is called the thylakoid membrane.
Plastids, like mitochondria, have their own genetic information. All plastids come from small organelles, the proplasts, which appear in meristematic cells and evolve when the adult cell differentiates, giving rise to one or another type of plast.
There are two main types of plastids:
- Leukoplasts. They are plastics that are colorless (they do not have pigments) and are responsible for storing substances, such as starch (amyloplasts), fats (oleoplasts) and proteins (proteoplasts). They are located in the plant cells that form the cotyledons, the first leaves that appear on the stem and in some parts of the root.
- Chromoplasts. They are plasts that contain a pigment that gives them color, such as chlorophyll (green color) and are called chloroplasts, and phycoerythrin (red color), called rhodoplasts.