This presentation will provide a description about the biosynthesis of plant growth regulator- Cytokinins and gibberalins and their role in plant growth and development

1. BIOSYNTHESIS AND
FUNCTIONS OF CYTOKININS
AND GIBBERALINS:
DR. GURPREET SINGH, Ph.D
Assistant Professor
Post-Graduate Department of Biotechnology
Lyallpur Khalsa College, Jalandhar (INDIA)
EMAIL: singh.gpbio@gmail.com

2. Carlos Miller et al in 1955 isolated a
“cell-division-stimulating factor” from
yeast DNA.
It was named as kinetin because of its
amazing power to stimulate cell
division (cytokinesis) in the presence of
an auxin.

6. CYTOKININS (Natural occurring)

9. methylerythritol phosphate (MEP
mevalonate (MVA) pathway

12. Biosynthesis of Cytokinin
• The first committed step in cytokinin biosynthesis is the addition of
the isopentenyl side chain from DMAPP to an adenosine moiety.
• The plant and bacterial IPT enzymes differ in the adenosine substrate
used; the plant enzyme appears to utilize both ADP and ATP, and the
bacterial enzyme utilizes AMP.
• The products of these reactions (iPMP, iPDP, or iPTP) are converted to
zeatin by an unidentified hydroxylase.

13. • The first committed step in cytokinin biosynthesis is the transfer of
the isopentenyl group of dimphate (DMAPP) to an adenosine moiety.
• In both cases, DMAPP and AMP are converted to
isopentenyladenosine-5′-monophosphate (iPMP).
• As with the free cytokinins, isopentenyl groups are transferred to the
adenine molecules from DMAPP by an enzyme called tRNA-IPT.
Biosynthesis of Cytokinin

14. Cytokinin Biosynthesis
Biosynthetic pathway for cytokinin biosynthesis. The first committed step in cytokinin biosynthesis
is the addition of the isopentenyl side chain from DMAPP to an adenosine moiety. The plant and
bacterial IPT enzymes differ in the adenosine substrate used; the plant enzyme appears to utilize
both ADP and ATP, and the bacterial enzyme utilizes AMP. The products of these reactions (iPMP,
iPDP, or iPTP) are converted to zeatin by an unidentified hydroxylase. The various phosphorylated
forms can be interconverted and free trans-Zeatin can be formed from the riboside by enzymes of
general purine metabolism. trans-Zeatin can be metabolized in various ways as shown, and these
reactions are catalyzed by the indicated enzymes.

25. GIBBERALINS
Gibberellins are tetracyclic diterpenoids made up of four isoprenoid units.
Terpenoids are compounds made up of five-carbon (isoprene) building blocks: joined head to tail.
the

29. STAGE A- which occurs in
plastids, leads to the synthesis
of the tetracyclic hydrocarbon,
ent-kaurene
STAGE B- which occurs in the
endoplasmic reticulum, ent-
kaurene is sequentially oxidized
to yield the first formed GA,
GA12 and its 13-hydroxylated
analog GA53.
STAGE C- which occurs in the
cytosol, GA12 and GA53 are
further oxidized to other C20-
GAs, and C19-GAs.

31. Buchanan, B et al., Biochemistry and Molecular Biology of Plants; chapter 17