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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

Growth HormoneCYTOKININ

Course: BOT 331Plant Physiology

March 11, 2009

Pankaj Jaiswal

Oregon State University

Corvallis, OR

1

regulates cell cycle
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.

crown gall formation
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

regulates morphogenesis
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
slide6

Cytokinin regulates root growth

Current Biology, Volume 17, Issue 9, R321-R323, 1 May 2007

slide9

Cytokinin oxidase regulates rice grain production.

Science DOI: 10.1126/science.1113373

slide10

CLV3

WUS

CLV1

WUSCHEL controls meristem function by direct regulation of cytokinin-inducible response regulators

shoot meristem activity by a cytokinin activating enzyme gene in rice log
shoot meristem activity by a cytokinin-activating enzyme gene in rice LOG

Nature 445, 652-655(8 February 2007)

cytokinin things to remember
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