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Growth Hormone CYTOKININ

Growth Hormone CYTOKININ Course: BOT 331Plant Physiology March 11, 2009 Pankaj Jaiswal Oregon State University Corvallis, OR 1 Suppresses growth of root by reducing cell size and cell division Regulates Cell Cycle

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Growth Hormone CYTOKININ

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  1. Growth HormoneCYTOKININ Course: BOT 331Plant Physiology March 11, 2009 Pankaj Jaiswal Oregon State University Corvallis, OR 1

  2. Suppresses growth of root by reducing cell size and cell division

  3. Regulates Cell Cycle Regulates the cell cycle/cell division (therefore, the name "cytokinins) – especially by controlling the transition from G2 phase of mitosis. This effect is moderated by cyclin-dependent protein kinases (CDK's) and their subunits, cyclins.

  4. Crown gall formation • tumor-like mass of undifferentiated cells that typically occurs near the crown (junction of root and stem) of the plant • caused by the bacterium Agrobacterium tumefaciens • carries a plasmid (Ti plasmid; a plasmid is a small loop of non-chromosomal DNA) with loci/genes for auxin production (tms), zeatin production (tmr) and opines (are nitrogen-containing molecules that provide food for the bacteria). • upon infection, the plasmid is incorporated into the plant cell genome which begins to overproduce auxin and cytokinin • stem forms an undifferentiated tumor (crown gall) • as predicted, if the tms genes (auxin production) are deleted from the plasmid, which would increase the cytokinin/auxin ratio, the resultant crown gall is "shooty". If the tmr genes are deleted the gall is "rooty". http://www.youtube.com/watch?v=L7qnY_GqytM

  5. Regulates morphogenesis • In plant tissue cultures, cytokinin is required for the growth of a callus. Callus is an undifferentiated, tumor-like mass of cells. Meristematic tissue properties): • callus + auxin + no cytokinin→little growth of callus • callus + auxin + cytokinin →callus grows well, undifferentiated • ratio of cytokinin and auxin are important in determining the fate of the callus: • callus + low [cytokinin/auxin]→callus grows well, forms roots • callus + high [cytokinin/auxin] →callus grows well, forms meristem & shoots • some tissues become habituated during repeated cell culture – loose the requirement for cytokinin in the growth medium

  6. Cytokinin regulates root growth Current Biology, Volume 17, Issue 9, R321-R323, 1 May 2007

  7. Promotes Chloroplast development

  8. Cytokinin Metabolism

  9. Cytokinin oxidase regulates rice grain production. Science DOI: 10.1126/science.1113373

  10. CLV3 WUS CLV1 WUSCHEL controls meristem function by direct regulation of cytokinin-inducible response regulators

  11. shoot meristem activity by a cytokinin-activating enzyme gene in rice LOG Nature 445, 652-655(8 February 2007)

  12. Cytokinin Signal Transduction

  13. Cytokinin: Things to Remember • Regulates morphogenesis • Suppresses growth of root by reducing cell size and cell division • Crown gall formation • Regulates cell cycle • Promotes Plastid/chloroplast development • They are Adenine derivatives. • Important first step of biosynthesis is committed by iso-pentenyl transferase • Cytokinin oxidase contributes to cytokinin catabolism • WUSCHEL controls meristem function by direct regulation of cytokinin-inducible response regulators • cytokinin-activating enzyme regulates shoot meristem activity • Cytokinin activity promotes Shot apical meristem activity also by abundant Nitrogen availability • Cytokinin signal transduction involves two-component signaling system

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