Leucoplast

What are Leucoplasts

Leucoplasts are a type of plastids, which are cellular organelles exclusively found in plant cells. Unlike other plastids, they are colorless, i.e., they do not contain any pigments. So, they have been named leucoplasts, as ‘leukos’ in Greek means ‘white’ and ‘plastos’ stands for ‘formed or molded’.

They are usually found in non-photosynthetic tissues such as endosperm, tubers, roots, bulbs, and seeds. They specialize in storing starch, protein, and lipids in plants. Leucoplasts may also perform biosynthetic functions such as synthesizing fatty acids, amino acids, and various other compounds.

Structure: What does it Look like

Leucoplasts are smaller than chloroplasts and have variable morphology, like oval, rod-like, or filamentous. They are bound by a double membrane and contain their own DNA and protein-synthesizing machinery. Their ground matrix is called stroma, which is less dense than chloroplasts stroma. They also lack grana and any pigments.

In epidermal cells of roots, hypocotyls, and petals, leucoplasts remain interconnected by extensive networks of stromules (stroma-filled tubules). During the development of certain cell types, leucoplasts cluster around the nucleus with stromules extending to the cell periphery.

Types with Functions

Based on the substance stored, leucoplasts are of three types:

1) Amyloplast

Amyloplasts convert glucose to starch and store it in tubers, seeds, stems, and fruit. They also synthesize transitory starch for photosynthetic parts. After synthesis, the starch is stored temporarily in chloroplasts and broken down at night to release energy when photosynthesis does not occur.

Stratoliths are special amyloplasts that involve the sensing of gravity in plants. They are exclusively found in plant roots. Here, the stored starch granules are denser than the cytoplasm and therefore are affected by gravity. This induces the growth of the root in a downward direction.

2) Elaioplast

These leucoplasts, also called oleosomes, synthesize fatty acids and store lipids in lipid-filled microcompartments called plastoglobuli. They play a key role in the development of pollen grains.

3) Proteinoplast

Also known as aleuroplasts, these leucoplasts store protein and are commonly found in seeds.

Difference between Leucoplast, Chloroplast, and Chromoplast

Characteristics	Leucoplast	Chloroplast	Chromoplast
1. Color	Colorless	Colored	Colored
2. Pigment	Does not contain pigments	Contains chlorophyll	Contains pigments, such as orange carotene, yellow xanthophylls, and various other red pigments
3. Occurrence	Found in roots, bulbs, and seeds	Found in green parts of plant, such as green leaves, and young stem	Found in the exposed parts of the plant including fruits, flowers, and stressed or injured leaves
4. Lamellae	Lamellae absent	Grana and stroma lamellae present	Lamellae absent
5. Relation with other plastids	Give rise to chromoplast and chloroplast	Change into chromoplast	Do not change into other types of plastids
6. Function	Store proteins, starch, and fats	Synthesizes carbohydrate by photosynthesis	Gives different colors to plant leaves, flowers, and fruits and help in attracting pollinators