Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): Callus proliferates from the internodal segments of tobacco stems only if the nutrient medium is supplemented with extracts of vascular tissues, yeast extract, coconut milk or DNA, in addition to auxins. Reason (R): These supplements provide cytokinesis-promoting active substances which are require

Step-by-step solution

Assertion (A) is correct because F. Skoog and his co-workers observed that auxin alone is insufficient for callus proliferation from tobacco stem internodes; it requires supplementation with specific extracts like yeast extract, coconut milk, or DNA. Reason (R) is correct and correctly explains the assertion because these supplements are sources of cytokinins (cytokinesis-promoting active substances like kinetin). Cytokinins and auxins act synergistically to promote cell division and callus growth in tissue culture