14. Certain plant species produce cyanogenic glycosides to protect them from pathogens. A researcher has identified a variant of such a plant that has higher level of cyanogenic glycoside yet it is highly susceptible to a specific fungal pathogen. To interpret this counter. intuitive observation, the researcher hypothesizes that the fungal pathogen has higher level of
    A. β-glucosidase activity
    B. formamide hydrolyase activity
    C. cytochrorne P-450 enzyme
    D. cyanide-resistant, alterative oxidase activity
    Which one of the following combinations of the above hypotheses is correct?
    (1) A and B
    (2) B and C
    (3) C and D
    (4) B and D

    Correct answer: (4) B and D

    Explanation:

    • Cyanogenic glycosides release hydrogen cyanide (HCN) when hydrolyzed by β-glucosidase, which is often present in the plant or pathogen.

    • The fungal pathogen’s high formamide hydrolyase activity can detoxify cyanogenic compounds by degrading cyanide derivatives, reducing the effectiveness of the plant’s cyanogenic defense.

    • The presence of a cyanide-resistant alternative oxidase (AOX) allows the fungal pathogen to bypass cyanide inhibition of respiration, thereby tolerating cyanide toxicity.

    • Cytochrome P-450 enzymes are involved in many metabolic pathways but are not specifically implicated in cyanide detoxification or cyanogenic glycoside resistance.

    Option-wise:

    • (1) A and B — β-glucosidase would increase toxicity, making susceptibility less likely; thus β-glucosidase alone does not explain susceptibility.

    • (2) B and C — C is unlikely to explain cyanide resistance.

    • (3) C and D — C unlikely.

    • (4) B and D — explains pathogen detoxification and cyanide resistance.

Certain fungal pathogens can overcome plant cyanogenic glycoside defenses by producing formamide hydrolyase that detoxifies cyanide derivatives and using cyanide-resistant alternative oxidase to maintain respiration, explaining increased susceptibility in plants with high cyanogenic glycosides.