Types of Plastids

There are two main groups of plastid, the chromoplasts and the leucoplasts are colorless plastids. Chromoplasts may be photosynthetically active, e.g. chloroplasts, pheoplasts, rhodoplasts and blue-green chromoplasts or may be without photosynthetic activity, e.g., carotenoids.

1. Chromoplasts

Chloroplasts. Most plastids contain the pigments chlorophyll a and b 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 the color, and are found in brown algae, diatoms and dinoflagellats.

Rhodoplasts contains the pigment phycoerythrin, and are found in the Rhodophyceac (red-algae).

Blue-green chromoplasts contain the pigments phycocyanin, phycoerytherin, chloroplyll a and carotenoids. They are found in the blue-green algae (now included in the Cyanobacteria.
In photosynthetic activity contain carotenoids, but have no chlorophyll. The color of carrots and tomatoes is due to the pigment present in the chromoplasts.

2. Leucoplasts

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 in endosperm, storage tubers and cotyledons. Leucoplasts which store oil are called elaioplasts, and those storing proteins are called aleuroneplasts.