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

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

Two main bioassays of brassinosteroid

1. Bean second-internode bioassay

For several days

Stem thickening, bending, and splitting

Two main bioassays of brassinosteroid

2. The rice lamina inclination

amounts of [BS]

Biological active brassinosteroids brassinolide (BLs), side chain structure

Ring A C-2 and C-3

Cis-vicinal glycol function

Ring B

7-membrane lactone

24-epiBL: often used

28-homoBL

form

Brassinosteroids biosynthesis pathways

DET2 encode

5α-reductase

CPD encodes

Cyto P450 monooxygenase

Why?

(CL)

(CT)

(TE)

Brz

(CS)

(BL)

Light grown

det 2 mutant wild

Dark grown

det 2 wild

BRs act locally near their sites of synthesis

Reciprocal grafting

wild root

Endogenous BRs do not seem to undergo root-to-shoot (a long-distance) translocation

wild shoot

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