Cytokinins are plant growth hormones that promote cell division. They were first isolated in the 1950s and have an adenine ring structure. There are two main types: adenine-type cytokinins like kinetin and zeatin, and phenylurea-type cytokinins like TDZ. Cytokinins induce cell division, delay senescence, promote nutrient movement and chloroplast development. They are synthesized by the enzyme isopentenyltransferase, which transfers an isopentenyl group to AMP. Cytokinins can also be produced through the degradation of tRNAs in plants and bacteria.

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,