Title: Growth Hormone CYTOKININ
1Growth HormoneCYTOKININ
- Course BOT 331Plant Physiology
- March 11, 2009
- Pankaj Jaiswal
- Oregon State University
- Corvallis, OR
1
2Suppresses growth of root by reducing cell size
and cell division
3Regulates 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.
4Crown 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
5Regulates 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
6Cytokinin regulates root growth
Current Biology, Volume 17, Issue 9, R321-R323, 1
May 2007
7Promotes Chloroplast development
8Cytokinin Metabolism
9Cytokinin oxidase regulates rice grain
production.
Science DOI 10.1126/science.1113373
10WUSCHEL controls meristem function by direct
regulation of cytokinin-inducible response
regulators
11shoot meristem activity by a cytokinin-activating
enzyme gene in rice LOG
Nature 445, 652-655(8 February 2007)
12Cytokinin Signal Transduction
13(No Transcript)
14Cytokinin 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