There are two main groups of plastids, the chromoplasts and the leucoplasts. The chromoplasts contain pigment, while the leucoplasts are colourless plastids. Chromoplasts may be photosynthetically active, e.g. chloroplasts, pheoplasts, rhodoplasts and blue- green chromoplasts, or may be without photosynthetic activity.e.g. carotenoids.
Chloroplasts. Most plastids contain the pigments chlorophyll a and b and are called chloroplasts. They are found in green algae and higher plants.
Pheoplasts contain the pigment fucoxanthin, which can absorb light and transfer the energy of chlorophyll. Pheoplasts are brown in colour and are found in brown algae, diatoms and dinoflagellates.
Rhodoplasts contain the pigment phycoerythrin, and are found in the Rhodophyceae (red- algae).
Blue-green chromoplasts contain the pigments phycocyanin, phycoerythrin, chlorophyll a and carotenoids. They are found in the blue-green algae.(now included in the Cyanobacteria).
In photosynthetic bacteria the chromoplasts contain the pigment bacteriochlorophyll. Chromoplasts which have no photosynthetic activity contain carotenoids, but have no chlorophyll. The colour of carrots and tomatoes is due to the pigment present in the chromoplasts.
Plastids without pigment are called leucoplasts. they are found in embryonic and sexual cells, and in regions of the plant not receiving light. Leucoplasts which function in the storage of starch are called amyloplasts. They are found iin endosperm, storage tubers and cotyledons. Leucoplasts which store oil are called elaioplasts, and those storing proteins are called aleuroneplasts.