Chapter 24 Brassinosteroids

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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 227 kg of bee-collected rape pollen
? 4 mg bioactive
brassin compound,
named brassinolide
X-ray analysis a polyhydroxylated
steroid,
a steroidal lactone
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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
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Two main bioassays of brassinosteroid 1. Bean
second-internode bioassay
For several days Stem thickening, bending, and
splitting
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Two main bioassays of brassinosteroid 2. The rice
lamina inclination
? amounts of BS
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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
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Brassinosteroids biosynthesis pathways
Why?
? Brz
(CL)
DET2 encode 5a-reductase CPD encodes
Cyto P450 monooxygenase
(CT)
(TE)
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(CS)
(BL)
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Dark grown det 2 wild
Light grown det 2 mutant wild
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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
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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