Brassinosteroid



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.[4][5] 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.[4]

BRs have been shown to be involved in numerous plant processes:
  • Promotes cell expansion and cell elongation;[4] works with auxin to do so[6]
  • It has an unclear role in cell division and cell wall regeneration[4]
  • Promotes vascular differentiation; BR signal transduction has been studied during vascular differentiation[7]
  • Is necessary for pollen elongation for pollen tube formation[8]
  • Accelerates senescence in dying tissue cultured cells; delayed senescence in BR mutants supports that this action may be biologically relevant[4]
  • Can provide some protection to plants during chilling and drought stress[4]

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. ^ Clouse SD, Sasse JM. 1998. Brassinosteroids: Essential regulators of plant growth and development. Annu. Rev. Plant Physiol. Plant Mol. Biol. 49:427–51
5. ^ Li JM, Chory J. 1997. A putative leucine rich repeat receptor kinase involved in brassinosteroid signal transduction. Cell 90:929–38
6. ^ Nemhauser et al. 2004. Interdependency of Brassinosteroid and Auxin Signaling in Arabidopsis. PLoS Biology
7. ^ Cano-Delgado A, 2004. BRL1 and BRL3 are novel brassinosteroid receptors that function in vascular differentiation in Arabidopsis. Development 131 :5341-5351
8. ^ 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

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Plant hormones (also known as plant growth regulators (PGRs) and phytohormones) are chemicals that regulate a plant's growth. According to a standard animal definition, hormones are signal molecules produced at specific locations, that occur in very low
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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
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B. napus

Binomial name
Brassica napus
L.

Rapeseed (Brassica napus), also known as Rape, Oilseed Rape, Rapa, Rapaseed
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Phytosterols (also called plant sterols) are a group of steroid alcohol, phytochemicals naturally occurring in plants. They are white powders with mild, characteristic odor, insoluble in water and soluble in alcohols.
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Arabidopsis
Heynh. in Holl & Heynh.

Species

See text.

Arabidopsis (A-ra-bi-dóp-sis, rockcress) is a genus in the family Brassicaceae. They are small flowering plants related to cabbage and mustard.
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Auxins are a class of plant growth substance (often called phytohormones or plant hormones). Auxins play an essential role in coordination of many growth and behavioral processes in the plant life cycle.
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vascular bundle is a part of the transport system in vascular plants. The transport itself happens in vascular tissue, which exists in two forms: xylem and phloem. Both these tissues are present in a vascular bundle, which in addition will include supporting and protective tissues.
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Plant hormones (also known as plant growth regulators (PGRs) and phytohormones) are chemicals that regulate a plant's growth. According to a standard animal definition, hormones are signal molecules produced at specific locations, that occur in very low
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Auxins are a class of plant growth substance (often called phytohormones or plant hormones). Auxins play an essential role in coordination of many growth and behavioral processes in the plant life cycle.
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Cytokinins (CK) are a class of plant growth substances (plant hormones) active in promoting cell division, and are also involved in cell growth, differentiation, and other physiological processes.
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Ethylene (or IUPAC name ethene) is the chemical compound with the formula C2H4. It is the simplest alkene. Because it contains a double bond, ethylene is called an unsaturated hydrocarbon or an olefin.
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jasmonates (JAs) are a group of plant hormones which help regulate plant growth and development. Jasmonates include jasmonic acid and its esters, such as methyl jasmonate (MeJa).
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polyamines are organic compounds having two or more primary amino groups - such as putrescine, cadaverine, spermidine, and spermine - that are growth factors in both eucaryotic and procaryotic cells.

Cyclen is the main representative of a class of cyclic polyamines.
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Salicylic acid (from the Latin word for the willow tree, Salix from whose bark it can be obtained) is a beta hydroxy acid (BHA) with the formula C6H4(OH)CO2H, where the OH group is adjacent to the carboxyl group.
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