Question

The combination of auxin and cytokinin, which is likely to induce shoot differentiation in tobacco callus is
(A) Lower concentration of cytokinin and Higher concentration of auxin
(B) Higher concentration of cytokinin and lower concentration of auxin
(C) only auxin
(D) only cytokinin

Answer 1

Hint: A developing mass of disorganised plant parenchyma cells is known as a plant callus. Callus cells are the cells that cover a plant wound in live plants. Callus development is generated in vitro from plant tissue samples (explants) following surface sterilisation and plating into tissue culture media in biological research and biotechnology. To begin callus development or somatic embryogenesis, the culture media is supplied with plant growth regulators such as auxin, cytokinin, and gibberellin. For all main families of terrestrial plants, callus initiation has been described.

Complete Step By Step Answer:
Auxins are a group of plant hormones (also known as plant growth regulators) that have morphogen-like properties. Auxins are necessary for plant body development and play a critical role in the coordination of numerous growth and behavioural processes in plant life cycles. The (dynamic and environment-responsive) pattern of auxin distribution inside the plant is a critical element in plant growth, environmental response, and, especially, plant organ development (such as leaves or flowers). It is accomplished by the so-called polar auxin transport system, which involves the complicated and well-coordinated active movement of auxin molecules from cell to cell throughout the plant body.
Cytokinins are a group of plant hormones that stimulate cytokinesis (cell division) in plant roots and shoots. They have a role in cell proliferation and differentiation, as well as apical dominance, axillary bud development, and leaf senescence. Many plant functions, such as cell division and shoot and root development, are influenced by cytokinins. Axillary bud development and apical dominance are known to be regulated by them. These effects, according to the "direct inhibition theory," are caused by the cytokinin-to-auxin ratio.
A callus is a clump of cells that is undifferentiated and contains totipotent cells. A high ratio of auxin-to-cytokinin or cytokinin-to-auxin drives root and shoot regeneration, respectively, whereas an intermediate ratio of auxin and cytokinin favours callus formation. It's been employed extensively in the spread of economically significant characteristics and the insertion of transgenes, for example.
Hence option B is correct.

Note:
Plant hormones are signal molecules generated by plants and found in extremely low amounts in the environment. Plant hormones regulate every element of plant development and growth, from embryogenesis through organ size regulation, pathogen defence, stress tolerance, and reproductive development.