Question

Name the various types of plastids. Where do fat soluble pigments occur.

Answer 1

Plastids are semi-autonomous organelles having DNA and double membrane envelope which store or synthesise various types of organic compounds. Depending upon their colour, plastids are of three main types- leucoplasts, chromoplasts and chloroplasts.

• Leucoplasts: They are colourless plastids which generally occur near the nucleus in non-green cells. They have variable size and form with stored nutrients. Granum is absent.

There are three types of special leucoplasts:

Amyloplast: They are starch-containing leucoplasts, e.g, potato tuber, rice, etc.

Elaioplasts: They store fats and ois, e.g., castor.

Aleuroplasts: They store proteins, e.g., aleurone grains of maize.

• Chromoplasts: These plastids are yellow, orange or reddish in colour because of the presence of carotenoid pigment. Chromoplasts are formed either from leucoplasts or chloroplasts. Change of colour from green to reddish during the ripening of tomato and chilli is due to transformation of chloroplasts to chromoplasts. The orange colour of carrot roots is due to chromoplasts.
• Chloroplasts: They are greenish plastids which possess photosynthetic pigments, chlorophylls and carotenoids and take part in the synthesis of food. Majority of the chloroplasts of the green plants are found in the mesophyll cells of the leaves. They vary in size, shape and number.

Chlorophyll, carotenoids and xanthophylls are the fat soluble pigments. They occur in chloroplasts.