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Any of a group of steroid derivatives that occur at very low concentrations in plant tissues and are potent plant hormones. Brassins have been found in pollen, leaves, stems, and flowers from various species; the most active form is brassinolide (BL). Extracts behave in a manner similar to auxins, for example stimulating elongation of hypocotyl and epicotyl tissue from seedlings when applied at concentrations as low as 10−7 mol dm−3. Brassins have various physiological effects, such as promoting growth by stimulating cell elongation and cell division. They have been shown to act synergistically with auxins and additively with gibberellins. BL binds to a membrane receptor called BRI1, thereby triggering downstream signal responses and ultimately regulating gene expression.

Subjects: Biological Sciences.

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