Question

In higher plants, zeatin is the most abundunt cytokinin. In addition, cytokinins can also occur as
(A). Riboside
(B). Thidiazuron
(C). Ribotide
(D). Glycoside
Choose the correct answer from the options given below:

• A. (A) only.
• B. (A), (C) and (D) only.
• C. (A) and (C) only.
• D. (C) and (D) only.

Hint:

Remember that zeatin riboside is the major form transported from the roots to the shoots through the xylem stream.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Cytokinins are adenine-derived plant hormones that promote cell division.
They exist in plant tissues in several interconvertible chemical forms, including free bases, nucleosides, nucleotides, and sugar conjugates.

Step 2: Detailed Explanation:
- Natural cytokinins like zeatin are modified adenine derivatives that exist in plants in several forms:
- Ribosides [A]: Converted by attaching a ribose sugar to the 9-nitrogen of the purine ring (e.g., zeatin riboside). This is the primary transport form of cytokinin in the xylem.
- Ribotides [C]: Cytokinin monophosphates containing a ribose-5-phosphate group at the N9 position. This is the initial form synthesized during de novo cytokinin biosynthesis.
- Glycosides [D]: Storage or inactive forms created by attaching glucose to the N3, N7, or N9 positions of the purine ring, or to the side chain oxygen.
- Thidiazuron (TDZ) [B]: A synthetic diphenylurea derivative with high cytokinin-like activity. It is used in plant tissue culture but does not occur naturally in plant tissues.
Therefore, the naturally occurring forms of cytokinins in plants are ribosides, ribotides, and glycosides.

Step 3: Final Answer:
The natural forms of cytokinin in plants are ribosides, ribotides, and glycosides.