Plant Physiology - Musienko M.M. 2001

Chemical and molecular composition, structure, and functions of the plant cell
Microbodies

In many Cells, small (about 2 µm), spherical microbodies bounded by their own membrane are found, containing various sets of Enzymes. Microbodies are specialized oval intracellular Organelles with a diameter of 0.2–1.5 µm, bounded by a single membrane and performing specific metabolic Functions. Their matrix has a finely granular Structure where specific enzymes or enzyme groups are localized. Among them are, for example, Lysosomes (cytosomes), which primarily contain hydrolytic enzymes. Enzymes that catalyze The breakdown of organic matter are concentrated within lysosomes, thereby remaining isolated from the rest of the Cytoplasm. Lysosomes remain intact until these enzymes come into contact with The Cell contents. However, even minor damage that causes their rupture releases the enzymes. As a result, biochemical processes involving lysosomes occur in The plant cell, which can sometimes be detrimental and at other times beneficial to the cell. For instance, they can be utilized to combat pathogens, specifically Viruses, Bacteria, or Fungi infecting the cell.

However, the most typical among them are Peroxisomes and glyoxysomes.

Peroxisomes are found in the photosynthetic leaf cells of higher plants, where they account for approximately one-third of the chloroplast content and half the mitochondrial content, maintaining close contact with these organelles (Photo 2).

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Photo 2. Interorganelle connections of a peroxisome (1) with a mitochondrion (2) and a chloroplast (3)

They contain A number of oxidative enzymes (catalase, glycolate oxidase) and are considered cellular compartments for detoxifying H₂O₂. Peroxisomes host specific stages of Photorespiration, which will be discussed in the chapter "Photosynthesis".

Another type of microbodies, glyoxysomes, is found in the Cells of the endosperm and cotyledons of fat-storing seeds. They were first isolated from the endosperm of germinating castor bean seeds in 1967. It was discovered that glyoxysomes appear only during germination and persist in cells as long as plant growth relies on reserve Lipids. Once the cotyledons emerge above the soil surface, fat utilization ceases, glyoxysomes disappear, and typical leaf peroxisomes emerge. This process is light-regulated.

Glyoxysomes are closely associated with fat-storing oval particles known as sphaerosomes. The primary function of glyoxysomes is to facilitate The conversion of stored fats into CARBOHYDRATES via Respiration during seed germination. Thanks to glyoxysomes, acetyl-CoA produced during the Oxidation of Fatty acid residues from reserve fats is not oxidized to CO₂ in the Krebs cycle, but is instead channeled into carbohydrate synthesis. Microbodies lack their own genetic mechanisms for formation; therefore, it is likely that other subcellular structures, such as The Endoplasmic reticulum, participate in their development. Microbody enzymes may be synthesized by Ribosomes of the rough ER, while their membranes differentiate and bud off from ER membranes.