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'Brassinosteroids' (BR) are a group of steroidal plant hormones. Brassinolide was the first of these steroid compounds discovered in 1973, when it was shown that pollen from ''Brassica napus'' could promote stem elongation and cell divisions and that the biologically active molecule was a steroid that the authors called 'Brassins'.^[1] Since their discovery over 70 BR compounds have been isolated from plants^[2]
The BR is biosynthesised from campesterol, the biosynthetic pathway was elucidated by Japanese researchers and later show to be correct through the analysis of BR biosynthesis mutants in ''Arabidopsis'', tomato and peas.^[3] The sites for BR synthesis in planta have not been experimentally demonstrated. One well-supported hypothesis is that all tissues produce BRs, since BR biosynthetic and signal transduction genes are expressed in a wide range of plant organs, and short-distance activity of the hormones also supports this.Clouse SD, Sasse JM. 1998. Brassinosteroids: Essential regulators of plant growth and development. ''Annu. Rev. Plant Physiol. Plant Mol. Biol.'' 49:427–51^[4] Experiments have shown that long distance transport is possible and flows in an acropetal direction, but it is not known if this movement is biologically relevant.
BRs have been shown to be involved in numerous plant processes:

★ Promotes cell expansion and cell elongation; works with auxin to do soNemhauser et al. 2004. Interdependency of Brassinosteroid and Auxin Signaling in Arabidopsis. ''PLoS Biology''

★ It has an unclear role in cell division and cell wall regeneration

★ Promotes vascular differentiation; BR signal transduction has been studied during vascular differentiation^[5]

★ Is necessary for pollen elongation for pollen tube formation^[6]

★ Accelerates senescence in dying tissue cultured cells; delayed senescence in BR mutants supports that this action may be biologically relevant

★ Can provide some protection to plants during chilling and drought stress

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References

1. Mitchell JW, Mandava NB, Worley JF, Plimmer JR, Smith MV. 1970. Brassins:a new family of plant hormones from rape pollen. ''Nature'' 225:1065–66
2. Bajguz, A. 2007. Metabolism of brassinosteroids in plants. ''Plant Physiology and Biochemistry'' 45: 95-107
3. Fujioka S, Sakurai A. 1997. Biosynthesis and metabolism of brassinosteroids. ''Physiologia Plantarum'' 100:710–15
4. Li JM, Chory J. 1997. A putative leucine rich repeat receptor kinase involved in brassinosteroid signal transduction. ''Cell'' 90:929–38
5. Cano-Delgado A, 2004. BRL1 and BRL3 are novel brassinosteroid receptors that function in vascular differentiation in Arabidopsis. ''Development'' 131 :5341-5351
6. Hewitt FR, et al. 1985. Effect of brassinolide and other growth regulators on the germination and growth of pollen tubes of Prunus avium using a multiple hanging drop assay. Aust. J. Plant Physiol. 12:201–11

External links

★ Brassinosteroid page