Plastids are double membrane bounded semi autonomous cell organelle responsible to synthesise and store various types of organic compounds.

On the basis of structure, pigments and function, the plastids can be categorized into three types:

1) Chloroplasts

2) Chromoplasts

3) Leucoplasts

However, one form of plastid can change into another form. For example: In tomato the young ovary contains Leucoplasts which change into chloroplasts in young fruits and finally into Chromoplasts as food ripens.

As detailed description about chloroplasts have been provided in previous notes let us discuss about Chromoplasts over here .

Chromoplasts 

• It is a coloured plastid which contains variety of pigments other than green.


• They are found in petals, ripe fruits, leaf of some plants, carrot root etc.


• It contains carotenoids (carotenes and xanthophyll)


• They are formed either from chloroplasts by the replacement of chlorophyll with other pigments pigments (eg:red pigment lycopene in tomatoes and chillies) or from Leucoplasts by the development of some pigments (eg: carotenes in carrot roots).


• They are structurally similar with chloroplast but lamella or thylakoid degenerate completely or partially. 

Types of Chromoplasts (based on colouring pigments)

1) Phaeoplast (Gr: phaeo: dark or brown; plast: living)

They contain brown pigments  (Xanthophyll and fucoxanthin). Eg: Brown algae, Diatoms.

2) Rhodoplasts 

They contain red pigment  (R-phycoerythrin, R- phycocyanin. They are found in red algae.

3) Chromatophores

They are found in blue green algae and contain c- phycocyanin, c- phycoerythrin and Chlorophyll-a. They are also found in purple photosynthetic bacteria.

Functions 

• It provides colour to flower and fruits which makes them attractive to attract insects and other animals who help in pollination and seed dispersal.


• 
  It is a site of phospholipid synthesis