20. According to the current model of alternative oxidase regulation, the following factors cause induction of atternative oxidase
(A) significant increase on the ubiquitin pool in the cytosol.
(B) Presence of a-keto acids (like pyruvate and glyoxylate.
(C) cold stress.
(D)  increase in cytosolic ATP concentration.
Which one of the following combinations of above statements is true?
(1) (A) and (D)                               (2) (B) and (C)
(3) (A) and (B)                               (4) (A) and (C)

Introduction

Alternative oxidase (AOX) is a crucial protein in plant mitochondria that facilitates cyanide-resistant respiration. Its regulation is essential for maintaining metabolic flexibility and stress adaptation, particularly under environmental and physiological triggers.

Explanation of Each Option

(A) Significant increase in the ubiquitin pool in the cytosol.

• Incorrect. Ubiquitin-mediated protein degradation does not directly induce AOX expression.

(B) Presence of a-keto acids (like pyruvate and glyoxylate).

• Correct. These metabolites act as positive effectors, enhancing AOX activity by stabilizing the enzyme’s reduced active form.

(C) Cold stress.

• Correct. Cold stress is known to induce AOX expression as part of plant stress response mechanisms.

(D) Increase in cytosolic ATP concentration.

• Incorrect. Elevated ATP generally signals energy sufficiency, which represses AOX induction.

Why Option (2) (B) and (C) Is Correct

AOX induction is stimulated by metabolites like a-keto acids and environmental stresses such as cold. This allows plants to optimize respiration and mitigate reactive oxygen species during stress conditions.

This understanding is valuable for researchers and students studying plant stress physiology and mitochondrial function.