brassinolide

Brassinolide is a plant hormone. The first isolated brassinosteroid, it was discovered when it was shown that pollen from rapeseed (Brassica napus) could promote stem elongation and cell division. The biologically active component was isolated and named brassinolide.

== Biosynthesis == The production of brassinolide begins with a closely related sterol called campesterol, which is found in the cell membrane. Initially, it is reduced by an enzyme called DET2. This is followed by a series of oxidation reactions, facilitated by cytochrome P-450 enzymes, which add hydroxyl groups to the molecule. The most biologically significant of these reactions is the C6 oxidation, where a ketone is formed at the C6 carbon position. This single reaction increases the biological activity of the molecule by a factor of 200. Depending on when this C6 oxidation occurs, it is referred to as either the early or late C6 oxidation pathway. Both of these synthetic pathways have been observed in Arabidopsis seedlings. It appears that the late C6 oxidation pathway predominates when the seedlings are exposed to light, while the early pathway is active in the absence of light. If the plant cannot perform C6 oxidation, it results in the "Dwarf phenotype," characterized by severe growth deficits.