1. Chapter 24 Brassinosteroids
novel growth-promoting substances in pollen
1970 Mitchel et al the pollen of rape plant (Brassica napus L.)
in the organic solvent fraction
physiological tests:
cell elongation, division, bending, swelling,
splitting of the second internode,
also increased total biomass and seed yield
1979 Grove et al kg of bee-collected rape pollen
 4 mg bioactive brassin compound,
named brassinolide
X-ray analysis: a polyhydroxylated steroid,
a steroidal lactone

2. the broadleaf evergreen tree Dystillium racemosum, a mixture of
1982 Yokota et al
chestnut galls purified castasterone, the precursor of brassinolide
1992 Abe and Yokota
the broadleaf evergreen tree Dystillium racemosum, a mixture of
biologically active brassinolide-like substance
1998 Clouse and Sasse
involved shoot growth, root growth, vascular differentiation,
fertility, and seed germination
Brassinosteroids have been identified in
27 families of seed plants, one pteridophyte, one bryophyte,
and one green alga
 ubiquitous plant hormone

3. Two main bioassays of brassinosteroid
1. Bean second-internode bioassay
For several days
Stem thickening, bending, and splitting

4. Two main bioassays of brassinosteroid
2. The rice lamina inclination
 amounts of [BS]

5. Biological active brassinosteroids
 brassinolide (BLs), side chain structure
24-epiBL: often used
Ring A C-2 and C-3
Cis-vicinal glycol function
 form
Ring B
7-membrane lactone
28-homoBL

6. Brassinosteroids biosynthesis pathways Why?
 Brz
(CL)
DET2 encode
5α-reductase
CPD encodes
Cyto P450 monooxygenase
(CT)
(TE)

7. (CS)
(BL)

8. Dark grown
det wild
Light grown
det 2 mutant wild

9. BRs act locally near their sites of synthesis
Reciprocal grafting
wild shoot
Endogenous BRs do not seem to undergo root-to-shoot (a long-distance) translocation
wild
root

10. BRs: effects on growth and development
fiber development in cotton
development of lateral roots
maintenance of apical dominance
vascular differentiation
male sterility (pollen tube growth)
plant defense (resistance to infection)
seed germination
leaf senescence
Small- scale studies and large-scale trials using BRs
 are bound to emerge,
is most beneficial to growth under stress conditions