Samenvatting Plant physiology H8: Brassinosteroids
Introduction:
• Plant steroids = flat sterol-like molecule consisting of 4 ring structures with no
endocyclic double bounds & a hydroxylation at position 3
• Hydrophilic & hydrophobic region
• Special bioassay with blades & sheets bending due to sclerenchyma cells
• Big diversity → C27-29 → C28 most active (brasinolide)
Brassinosteroids Biosynthesis:
• Starts with terpenoid biosynthesis again → terpenoid squalene is precursor of steroid
cycloartenol
• You then have 3 BR sterol precursors after that
o Cholesterol C27
o Campesterol C28 (preferred)
They share enzymes
o Sitosterol C29 (most abundant)
, • Metabolic grid model → different routes to get to the active brassinolide
o Contains different enzymes
▪ DWF4 = CYP90B/C/D1 → brassinazole (BRZ) as inhibitor
▪ DET2 = C-5--reductase activity
▪ CYP85A1/2 = C-2, C-6, C-7 oxidation → Last enzyme that in the last
step converts the active castasterone precursor BR into brassinolide
which is the most active BR
o Expression of BR happens everywhere in the plant
o The CYP proteins are ER localized → BR production in the ER & affinity for lipid
bilayers
• Metabolization of castasterone & brassinolide → different ways in different species
Introduction:
• Plant steroids = flat sterol-like molecule consisting of 4 ring structures with no
endocyclic double bounds & a hydroxylation at position 3
• Hydrophilic & hydrophobic region
• Special bioassay with blades & sheets bending due to sclerenchyma cells
• Big diversity → C27-29 → C28 most active (brasinolide)
Brassinosteroids Biosynthesis:
• Starts with terpenoid biosynthesis again → terpenoid squalene is precursor of steroid
cycloartenol
• You then have 3 BR sterol precursors after that
o Cholesterol C27
o Campesterol C28 (preferred)
They share enzymes
o Sitosterol C29 (most abundant)
, • Metabolic grid model → different routes to get to the active brassinolide
o Contains different enzymes
▪ DWF4 = CYP90B/C/D1 → brassinazole (BRZ) as inhibitor
▪ DET2 = C-5--reductase activity
▪ CYP85A1/2 = C-2, C-6, C-7 oxidation → Last enzyme that in the last
step converts the active castasterone precursor BR into brassinolide
which is the most active BR
o Expression of BR happens everywhere in the plant
o The CYP proteins are ER localized → BR production in the ER & affinity for lipid
bilayers
• Metabolization of castasterone & brassinolide → different ways in different species
