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DISCOVERY OF CYTOKININS
• SEARCH FOR CELL DIVISION FACTORS THAT WOULD ALLOW
PLANT TISSUES TO DIVIDE IN TISSUE CULTURE
• CELL DIVISION ACTIVITY IDENTIFIED IN COCONUT MILK
•CELL DIVISION ACTIVITY ALSO FOUND IN VASCULAR TISSUES
•ADENINE FOUND TO BE SLIGHTLY ACTIVE
• OLD BOTTLE OF DNA FOUND TO HAVE STRONG ACTIVITY, BUT
NOT NEW BOTTLE
• KINETIN IDENTIFIED AS DEGRADATION PRODUCT OF DNA
KINETIN (6-furfurylaminopurine)
(Discovered
as a cell
division
factor)
STRUCTURE OF BENZYLADENINE (BA) - ANOTHER
SYNTHETIC CYTOKININ
trans-Zeatin
(The Naturally Occurring Cytokinin)
Biological isoprene
unit
(active form)
CYTOKININ DEGRADATION
EFFECT OF
CYTOKININ
DEFICIENCY
ON GROWTH
OF TOBACCO
PLANTS
Tobacco plants
overexpressing
gene for cytokinin
oxidase
WILD TYPE
Wild-type Tobacco
Tobacco overexpressing cytokinin oxidase
Wild-type
CO
Overexpressor
Wildtype root
tip
CO
Overexpressor
root tip
 Cytokinin
inhibits root
growth
INCREASING CK CONCENTRATION
INCREASING IAA CONCENTRATION
OVEREXPRESSION OF Cyclin D3 (CYCD3) BYPASSES
THE CYTOKININ REQUIREMENT FOR CELL DIVISION
Crown gall tumor on tomato
stem
(Agrobacterium tumefaciens)
• TWO MAJOR
OPINES
FOUND IN
CROWN GALL
TUMORS
• GENES FOR
OPINE
SYNTHESIS
PRESENT ON
T-DNA FROM
AGROBACTE
RIUM
Witches’ broom on
balsam fir
(Corynebacterium
fascians)
Protonemal filaments of the moss, Funaria. (Control)
Protonemal filaments of the moss, Funaria. (Treated with
Benzyladenine)
BUD FORMATION IN THE MOSS, Funaria
EFFECT OF CYTOKININ ON LEAF SENESCENCE
CYTOKININTREATED
CYTOKININ CAUSES CELLS TO BECOME SINKS
CYTOKININ
INHIBITS
SENESCENCE
CYTOKININ PROMOTES EXPANSION OF RADISH COTYLEDONS
CYTOKININ SIGNALING INVOLVES A TWOCOMPONENT SYSTEM