Q.28 Determine the correctness or otherwise of the following Assertion (a) and Reason (r).
Assertion: Immobilization of plant cells can enhance secondary metabolite production during
bioreactor cultivation.
Reason: Immobilization protects the plant cells from shear forces in the bioreactor.
(A) Both (a) and (r) are true and (r) is the correct reason for (a).
(B) Both (a) and (r) are true but (r) is not the correct reason for (a).
(C) (a) is true but (r) is false.
(D) (a) is false but (r) is true.
Correct Answer: (A) Both (a) and (r) are true and (r) is the correct reason for (a). Immobilization boosts secondary metabolite production by shielding plant cells from bioreactor shear, enabling stable, high-density cultures for sustained biosynthesis.
Assertion-Reason Analysis
Plant cells in suspension cultures suffer shear damage from agitation and aeration in bioreactors, limiting secondary metabolite yields like alkaloids and flavonoids. Immobilization via entrapment in alginate or polyurethane protects cells while promoting differentiation and product secretion.
Why Both Are True
Assertion (a): Immobilized plant cells achieve 2-10 fold higher secondary metabolite production (e.g., taxol from Taxus, rosmarinic acid from Coleus) due to prolonged viability and elicitor responsiveness in continuous bioreactors.
Reason (r): Bioreactor impellers generate shear rates >10,000 s⁻¹, rupturing fragile plant cells; immobilization matrices (gels, hollow fibers) absorb forces, reducing lysis by 80-90% and stabilizing non-growth-associated metabolism.
Option Breakdown
Option (B): Incorrect—protection from shear directly enables long-term cultivation, the primary mechanism for enhanced production over free cells.
Option (C): Incorrect—reason holds true; shear protection is well-documented in airlift and stirred-tank bioreactors for plant cells.
Option (D): Incorrect—assertion is true; studies confirm immobilization outperforms suspensions for anthraquinones, ajmalicine, and berberine.
Bioprocess Engineering Insights
Immobilized systems use fluidized/fixed-bed bioreactors for continuous operation, overcoming feedback inhibition via two-phase cultures. This scales sustainable production of pharmaceuticals, reducing reliance on wild harvesting.
