Cytokinins - Structure, Functions and Uses

Aug 24, 2023, 16:45 IST

Plants are different in many aspects despite arising from a single unit- the zygote. The changes in the growth, habitat, appearance, and composition of plants are brought about by plant hormones. Several classes of plant growth regulators (PGRs) like auxins, gibberellins, cytokinin’s, abscisic acid, and ethylene are known to influence the development of plants. Cytokinins especially have distinct effects on cytokinesis or cell division in plants.

Introduction

Cytokinins were first identified as kinetin, a modified form of the purine base ‘adenine’ derived from the DNA of autoclaved herring sperm. Plants do not produce kinetin naturally. Kinetin is a synthetic form of cytokinins which is chemically named as 6-Furfuruyl amino-purine. It was discovered by Miller in 1955.

Lethan discovered Zeatin in 1964. This natural cytokinin was extracted by isolating it from coconut milk and corn kernels during the search for naturally occurring compounds with cytokinin-like properties.

After zeatin was discovered, other naturally occurring cytokinins as well as some synthetic substances have been found that promote cell division.

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Synthesis

Natural cytokinins are produced in areas where cell division happens quickly, such as the apices of roots, growing shoot buds, early fruits, etc. It promotes the growth of lateral shoots, chloroplasts, and the production of adventitious roots. Apical dominance wherein the primary axis elongates but checks the growth of the other plant parts, can be prevented by using cytokinins. They encourage the mobility of nutrients, which helps to postpone the senescence of leaves. Cytokinins act in the opposite action to auxins. They move in a basipetal and polar manner.

Natural cytokinins- zeatin, isopentenyl adenine

Synthetic cytokinins- Kinetin, thidiazuron (TDZ), diphenylurea, benzyl adenine.

Structure

The term "cytokinin" was first proposed by three scientists named Strong, Miller, and Skoog. It is a substance that causes cytokinesis, or cell division, in the different plant organs grown on media with an ideal auxin concentration. This Plant growth regulator was first given the name "kinin" but later renamed cytokinin. All of the cytokinins that are found in nature have substituted purines. A cytokinin is typically named by expressing it as an N6-substituted adenine or a substituted 6-amino purine. Lethan isolated 6,4-hydroxy-3-methyl but-trans-2-enoyl amino purine from young Zea mays kernels and named it Zeatin.

The Function of Cytokinins

1. The hormones cytokinins are crucial for plants as they control the size of the shoot meristem and the growth of the leaf and shoot by encouraging cell division besides generating leaf primordium.
2. These PGRs can promote axillary bud differentiation and expansion. The cytokinins can facilitate the liberation of the axillary bud from apical dominance.
3. Cytokinins act in contrast to auxins and prevent the development of lateral roots in the root system of the plant.
4. Cytokinins also regulate the intake of minerals, the transport of nutrients, and the morphogenesis of vascular tissues (xylem and phloem) in the roots.
5. Cytokinins are necessary for the formation of chloroplasts and hence, are crucial in regulating the rate of photosynthesis.
6. They can also encourage flower primordia differentiation, prevent seed or bud dormancy, and postpone the senescence or aging of leaves and flowers.

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Cytokinin’s FAQs

Q1. What are Plant Growth Regulators or PGRs?

Ans. Plant Growth Regulators are those hormones that influence the growth and development of plant parts. Some essential PGRs include auxins, cytokinins, abscisic acid, gibberellins, and ethylene.

Q2. What are Cytokinins?

Ans. Cytokinins are those plant hormones that affect cell division or cytokinesis in plant cells. They promote cell proliferation in the root and shoot systems and act contrary to auxins.

Q3. Give the names of some naturally occurring cytokinins.

Ans. The first natural cytokinin was discovered from immature kernels of Zea mays by Lethan in 1955. It was named Zeatin. Another natural cytokinin is isopentenyl adenine.

Q4. Give the names of some synthetically produced cytokinins.

Ans. The first synthetic cytokinin was produced by Miller in 1964 by autoclaving DNA present in the sperms of herring. It was named Kinetin. Other synthetic cytokinins are thidiazuron (TDZ), diphenylurea, and benzyl adenine.

Q5. List three functions of cytokinins.

Ans.

1. The hormones cytokinins are crucial for plants as they control the size of the shoot meristem and the growth of the leaf and shoot by encouraging cell division besides generating leaf primordium.
2. These PGRs can promote axillary bud differentiation and expansion. The cytokinins can facilitate the liberation of the axillary bud from apical dominance.
3. Cytokinins also regulate the intake of minerals, the transport of nutrients, and the morphogenesis of vascular tissues (xylem and phloem) in the roots.

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