Phytochromobilin

Phytochromobilin is a tetrapyrrole chromophore that is involved in the photosensory perception of plants. It is a linear tetrapyrrole and is synthesized from heme in the plastids of plant cells.

Structure and Function

Phytochromobilin is a linear tetrapyrrole that is synthesized from heme in the plastids of plant cells. It is the chromophore of phytochrome, a protein that is involved in the photosensory perception of plants. Phytochromobilin absorbs light in the red and far-red regions of the spectrum, and this absorption triggers a conformational change in the phytochrome protein that leads to changes in gene expression.

Phytochromobilin is covalently attached to the phytochrome protein via a thioether bond to a cysteine residue. The attachment of phytochromobilin to phytochrome is a post-translational modification that is catalyzed by the enzyme phytochromobilin:protein lyase.

Biosynthesis

The biosynthesis of phytochromobilin begins with the oxidation of heme to biliverdin IXα by the enzyme heme oxygenase. Biliverdin IXα is then reduced to 3Z-phytochromobilin by the enzyme phytochromobilin:ferredoxin oxidoreductase. This reaction is unique to plants and algae, and it is the final step in the biosynthesis of phytochromobilin.

Role in Plant Development

Phytochromobilin plays a crucial role in plant development. It is involved in the regulation of seed germination, stem elongation, leaf expansion, chloroplast development, and flowering time. The absorption of light by phytochromobilin triggers changes in gene expression that lead to these developmental responses.

See Also

• Phytochrome
• Chromophore
• Tetrapyrrole
• Heme
• Biliverdin IXα
• 3Z-phytochromobilin