Question

First natural cytokinin was discovered by
A. Miller
B. Letham
C. Calvin
D. Haberlandt

Answer 1

Cytokinin is a plant hormone. Therefore, just like the hormones of the human body, plant hormones influence the growth of the plant. They are also called plant growth regulators or phytohormones. Apart from cytokinin other important plant hormones include ethylene, auxin, gibberellins, and abscisic acid. While ethylene and abscisic acid are growth inhibitors, the other three promote plant growth.

Complete answer:
Dr. Letham in 1963 isolates zeatin which is a naturally occurring cytokinin from immature corn kernels. Melvin Calvin is an American biochemist who discovered calvin cycle in plants. Haberlandt was a Austrain botanist who is the first person to study plant tissue culture.

The natural cytokinin was discovered by Folke Karl Skoog and Carlos Miller. They noted that the cells of the internodal region of the tobacco stem showed cell division only when some other substances were present in addition to auxin. Those substances that brought about cell division were either an extract of the vascular tissue, coconut milk, yeast cells, or DNA extracts. All these substances had something that contributed to cell division. This substance was isolated from herring sperm DNA and named it Kinetin.

It was later renamed cytokinins. It is a chemical name is $6$- furfurylaminopurine. It is as the name suggests a purine and can be derived from adenine. They are usually synthesized in the roots; however, any other actively dividing region can also synthesize this hormone. After being synthesized in the roots the hormone can move to the xylem and from there to the leaves and fruits.

Hence, the correct answer is option (A)

Note: Cytokinins cannot work alone; they can influence plant growth only in the presence of other plant hormones. For example, an equal concentration of both auxin and cytokinin can produce callus (that can give rise to other parts of the plant) because this combination will lead to the formation of cells that are not differentiated. This is useful in tissue culture.