Growth Hormone CYTOKININ

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?vL7qnY_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
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
(No Transcript)
14
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