Chemical nature of cytokinin:
Chemical nature of cytokinins is based on two types:
1. Adenine-type cytokinins
2. Phenylurea-type cytokinins

Adenine-type: These cytokinins are represented by kinetin, zeatin and 6-benzylaminopurine. Majority of the adenine-type cytokinins are synthesized in the roots. Cytokinin biosynthesis also takes place in the cambium and other actively dividing tissues.

Phenylurea-type: These cytokinins are represented by diphenylurea and thidiazuron (TDZ). Till now there is no evidence that the phenylurea cytokinins occur naturally in plant tissues.

Cytokinins are involved in both local and long distance signaling. Cytokinins are transported within the xylem.

Classes of cytokinin:
There are two classes of cytokinin hormone: They are as follows:}

(i) Natural cytokinin
(ii) Synthetic cytokinins

(i) Natural Cytokinin:

The most common form of naturally occurring cytokinin in plants today is called zeatin which was isolated from corn (Zea mays). Approximately 40 different structures of cytokinin are known. Other naturally occurring cytokinins include dihydrozeatin (DHZ) and isopentenyladenosine (IPA). Figure 7depicts some cytokinins.

Figure 7: Cytokinins