Cytokinin Biosynthesis

1. CYTOKININ

2. Biosynthesis of Cytokinin
• Cytokinins (CK) are a class of plant growth substances
(Phytohormones) that promote cell division, in plant roots and
shoots.
• The first cytokinin (Kinetin) was isolated in 1955 by Miller
• The first naturally occurring cytokinin (Zeatin) was isolated in 1961 by
Miller..
• All cytokinins have a basic Adenine ring structure
There are two types of Cytokinins:
Adenine type cytokinin (Kinetin, Zeatin and BAP) and phenylurea type
cytokinins (TDZ)

3. Functions of Cytokinin
• Induce cell division in presence of Auxin
• Delay senescence of leaves
• Promote the movement of nutrients
• Promote chloroplast development
• Promote cell expansion in leaves
• Regulate growth of stems and roots

4. Biosynthesis of Cytokins
• An enzyme that synthesise cytokinin is called – Isopentenyl –
pyrophosphate : AMP transferase or cytokinin synthase
• Isopentenyl group of IPP transferred to the AMP with the help of
prenyl transferase
• The product of this reaction is Isopentenyl adenine ribotide
• And is readily converted to Zeatin and other cytokinins

5. Cytokinin Biosynthesis
• Cytokinins can also be produced by recycled tRNAs in plants and
bacteria
• tRNAs with anticodons that start with a uridine and carrying an
already prenylated adenosine adjacent to the anticodon release on
degradation the adenosine as a cytokinin
• The prenylation of these adenines is carried out by tRNA-
isopentenyltransferase.

6. Biosynthesis of cytokinin
• Adenosine phosphate-isopentenyl transferase (IPT) catalyzes the first
reaction in the biosynthesis of isoprene cytokinins.
• It may use ATP,ADP, or AMP as substrates and may use Dimethylallyl
pyrophosphate (DMAPP) or Hydroxy methyl butenyl pyrophosphate
(HMBPP) as prenyl donors.
• This reaction is the rate-limiting step in cytokinin biosynthesis.
• DMADP and HMBDP used in cytokinin biosynthesis are produced by
the methylerythritol phosphate pathway (MEP)

7. In Plants and bacteria
• Cytokinins can also be produced by recycled tRNAs in plants and
bacteria
• tRNAs with anticodons that start with a uridine and carrying an
already-prenylated adenosine adjacent to the anticodon release on
degradation the adenosine as a cytokinin
• The prenylation of these adenines is carriedout by tRNA-
isopentenyltransferase
• Auxin is known to regulate the biosynthesis of cytokinin.

8. Synthesis of ABA
• https://www.slideshare.net/MandeepSaini45/abscisic-acid-
146268515?qid=5890a752-5e49-49e7-a44a-
90a1cbacd691&v=&b=&from_search=10
• Dt. 22-12-2022
• Abs: 12 and 13

9. • Thank you,