Plastids

A type of sub-cellular organelle found in plants

Plastids are small, semi-independent units scattered throughout the cytoplasm of plant cells. They contain their own DNA and ribosomes (protein factories), which they use to synthesise some of their own essential proteins. Plastids replicate by division.

There are several different types of plastids:

• Chloroplasts: Contain green chlorophyll and carry out photosynthesis
• Proplastids: Undifferentiated plastids found in young, undifferentiated cells (meristem cells)
• Leucoplasts: Primarily serve as sites for the synthesis of starch and oils
• Chromoplasts: Contain pigments - responsible for the colouring of fruits
  

Plastids can change from one type to another depending on the development of the cell.

Researchers are working on genetically modifying plastids. Unlike the DNA harboured in the nuclear genome of plant cells, plastid DNA is excluded from pollen. This could be an important containment strategy for transgenic plants. Plastid DNA accounts for one to 25 percent of the DNA in a plant cell.