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Organelles formed by a two-unit membrane envelope internally containing a matrix or stroma, where is a system of flattened saculiform membranes, the tilacoids.
They originate from plastids and contain DNA and ribosomes. They are divided into three major groups:
- chromoplast and
- leukoplast; These, in turn, originate from very small structures, proplastids (which normally already occur in the oosphere, embryonic sac and meristematic systems). When proplastids develop in the absence of light, they have a special system derived from the inner membrane, resulting in tubes that fuse and form the prolamellar body. These plastos are called stioplasts.
Its genome encodes some specific proteins of these organelles; contain chlorophyll and are associated with the light phase of photosynthesis, being more differentiated in the leaves. Its tilacoid system is made up of disc-shaped membrane cells called granus; It is in this system that chlorophyll is found. In the matrix there are carbon dioxide fixation reactions for carbohydrate production, as well as amino acids, fatty acids and organic acids. There may be starch and lipid formation, the latter in the form of globules (plastoglobules).
They carry carotenoid pigments (usually yellow, orange or reddish); They are found in colorful structures such as petals, fruits and some roots. They arise from chloroplasts.
Without pigments; can store several substances:
- Amyloplasts: Store starch. Eg in English potato tubers (Solanum tuberosum).
- proteinoplasts: store proteins.
- elaioplasts: store lipids. Eg avocado (Persea americana).