Microbodies

Single unit membrane bound, small spherical structures (9.3-1.5 µm in diameter).

On the basis of functions, microbodies are of three types:

1. Spherosomes

Hanstein (1880) first observed them and called as microsomes. Perner (1953) named them spherosomes.

Occur only in plant cells, and are major site of lipid storage and synthesis have lysosome-like activity, so also termed as plant lysosomes.

Sudan stain or osmium tetraoxide is used to stain spherosomes.

2. Peroxisomes or Uricosomes

Discovered by Rhodin and Tolbert

In animal cells peroxisomes are concerned with peroxide metabolism. Urate oxidase, Amino acid oxidase and peroxidase catalyse the oxidation of amino acids producing H₂O₂. Catalase degrade the H₂O₂ into water and oxygen.

In plants, peroxisomes occur in cells of green tissues and are concerned with photorespiration (glycolate pathway) and are also involved in -oxidation of fatty acids.

3. Glyoxysomes

Discovered by Rhodin, Beever and Briedenbach.

Fig. Structure of glyoxysome

Occur only in plants especially in fatty seeds, guard cells of stomata and unripe fruits.

Glyoxylic acid cycle takes place in Glyoxysome which was discovered by Kreb and Kornberg and is a variant of Kreb’s cycle.

Significance of Glyoxylic acid cycle :

(1) Involved in the formation of different organic acids during ripening of fruits.

(2) Converts fats into carbohydrates during germination of fatty seeds.

(3) May convert organic acids into carbohydrates (concerned with mechanism of closing of stomata during night)

(4) Glyoxalate is precursor of two amino acids, glycine and serine.

In addition to enzymes for glyoxylate cycle, the glyoxysomes also contain catalase and H2O2 generating glycolic oxidase. Therefore considered as highly specialised peroxisomes.