Cytokinins are plant hormones that influence various physiological functions, synthesized primarily in roots and transported to shoots. They regulate processes like cell division, shoot and root initiation, and play a significant role in leaf senescence. The document discusses the biosynthesis, transport, and physiological effects of cytokinins, highlighting their complex interactions with other hormones such as auxins.

1. Cytokinins
Dr. Emasushan Minj
Assistant Professor
Department of Botany
St. Xavier’s College,
Mahuadanr, Latehar
Nilamber Pitamber University

2. Introduction
• Cytokinins are that have
diverse effects on important physiological functions in plants.
• Naturally occurring cytokinins are adenines, which possess
either an isoprenoid or aromatic side chain at the N6
position.
• The first cytokinin was isolated from autoclaved herring
sperm in .
• This compound was named kinetin because of its ability to
promote cytokinesis.
• The first naturally occurring cytokinin was isolated from corn
by independently and it was called
Zeatin.

3. Biosynthesis and transport
 The common active cytokinins
are-
 Cytokinins are generally found
in
 They are believed to be
synthesized in the roots and
translocation via the xylem to
shoots.
 Its biosynthetic pathway takes
place through the
.

4. Physiological effects
 Cytokinin is involved in the formation, maintenance and growth of
the shoot apical meristem.
 They are positive regulators - for cell division in the shoot apical
meristem
and negative regulators -for cell division in the .
 They are involved in the .
 Direct application of cytokinins to axillary buds -
in the many
species, dominant the inhibitory effect of the shoot apex.

5.  Cytokinin and auxin stimulate morphogenesis (shoot and root
initiation) in the callus.
 When is present alone or if the ratio of auxin to cytokinin is
high- callus will initiate root formation.
 Likewise if is present in high concentration- promotes
shoot formation.
 Equal amount of both hormones results- the proliferation of
undifferentiated callus.
 Example- crown gall formation in Agrobacterium tumefaciens.

6.  Cytokinins promote the
through stimulation of chlorophyll synthesis.
 Dark-grown seedlings are said to be etiolated.
 The internodes of etiolated seedlings are more elongated and
chloroplasts do not mature.

, which contain
protochlorophyll instead of the chloroplast thyllakoid system
and do not synthesize most of the enzymes and structural
proteins for the formation of chloroplast thylakoid system and
photosynthesis machinery.

7.  Senescence is an essential process of the plant’s growth and
development.
 It is an
which leads to organ death.
 Hormones are key signal molecules that accelerate or delay the
timing of leaf senescence. Some hormones are positive regulators of
senescence, while others act as negative regulators.
 Same hormones can also act as both depending on the age of the
leaf.
 Positive senescence regulators -
 Negative senescence regulators–

8. Thankyou