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

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

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 24-epiBL: often used Ring A C-2 and C-3 Cis-vicinal glycol function  form Ring B 7-membrane lactone 28-homoBL

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

(CS) (BL)

Dark grown det 2 wild Light grown det 2 mutant wild

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

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