Question

State whether the following statements are true or false.
An undifferentiated plant callus in tissue culture is stimulated to differentiate by the relative amounts of auxin and cytokinin present.

Answer 1

Callus is the undifferentiated mass of cells which is obtained in the micropropagation of plants in plant tissue culture. From the callus depending on the phytohormones we provide, changes can be brought.

Complete answer:
A differentiated callus is dependent upon the concentration of phytohormones auxin and cytokinin. Auxin is a phytohormone synthesized at the tip of the stem (above the region of elongation) that endorses cell elongation. Five major types of auxins that are endogenous are indole-3-acetic acid, 4-chloroindole-3-acetic acid, phenylacetic acid, indole-3-butyric acid, and indole-3-propionic acid. Auxin promotes the growth of root and cell elongation in plants.
Cytokinins are other types of phytohormones which help in the formation of shoot and multiplication of cells. In the absence of plant growth regulators, a callus will only continue to divide cells and will stop after a particular time when nutrients are not provided. The presence of auxin and cytokinin in the specific ratio will differentiate the cells of the callus.
So, the correct statement is 'True'.

Note: -Auxin develops at the tip of the stem. Its movement is largely basipetal. Auxin travels towards the shadier side of the plant making the cells in that region grow longer than the other cells on the brighter side of the plant.
-Formation of callus is done in sterile lab conditions only because the media which provides growth for callus is rich in nutrients, which can turn into a growing ground for bacteria and contaminate callus.
-When auxin comes into contact with plant cells, it creates drastic changes in the expression of genes. Active research is still going on to know the precise mechanisms by which this occurs, and two auxin signaling pathways are almost completely investigated.