Brassinosteroid

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Brassinolide appears to be the most common Brassinosteroid.

Brassinosteroids (BAs), or Brassins, are a group of plant hormones. These steroid compounds were first discoved in rapeseed plant (Brassica napus) pollen. The most known example of brassinosteroids is brassinolide shown in the figure on the right.

[edit] Location, Characteristics and Occasions for Synthesis Induction

Released in mature cells (and less so in immature cells) when they have less than enough sugar and oxygen to support both themselves and any dependent cells
Released in response to root environmental, pest, or disease stress

May work in concert with gibberellin or be part of the hormone effect cascade
Is visually similar to the animal hormone cortisol and may function in a similar manner, raising phloem sugar levels to deal with short term environmental stress just like cortisone.

[edit] Effects

It can inhibits leaf abscission, the metabolism of cells in the root and root growth;
It enhances the rate of stem elongation.
It possibly enhances the production of ethylene indirectly by the causation of root cell senescence while it increases auxin response
Xylem differentiation can be promoted by these compounds in order to transfer resources from cannibalized root cells. Stressed Shoot is resistant to the stress because of rerouting resources from the root to the shoots..
It involves in gravitropism and bending of grass leaves at the sheath or blade joints.
It can acts as an indicator of poor shoot efficiency and low sugar and gases.
Thus all its effects, such as inhibiting root growth, possibly inhibiting root metabolism, possibly releasing stored sugars and gases and promoting shoot growth may be an attempt to increase sugar and essential gases.
For example at night when little light is available to make sugar, there may be high levels of BA.
BAs regulate the expression of numerous genes, impact the activity of complex metabolic pathways, contribute to the regulation of cell division and differentiation, and help control overall developmental programs leading to morphogenesis.
They are also involved in regulating processes more specific to plant growth including photomorphogenesis and skotomorphogenesis
They promote cell expansion in the presence of a potentially growth-limiting cell wall.