21. Which of the following staternents with respect to altenate oxidase activity on cyanide- resistant respiration in plants. is not correct?
(1) Alternate oxidase accepts electrons directly from cytochrorre C
(2) Some plants exhibit thermogenesis during inflorescence development.
(3) Transcription of alternate oxidase gene is often induced by various abiotic stresses.
(4) When electrons pass to alternate oxidase, two sites of proton pumping are bypassed.
Introduction
Alternate oxidase (AOX) plays a pivotal role in cyanide-resistant respiration in plants, providing a bypass for the mitochondrial electron transport chain. This pathway is critical for stress response and thermogenesis, allowing plants to maintain respiration under inhibitory conditions.
Explanation of Each Option
(1) Alternate oxidase accepts electrons directly from cytochrome c.
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Incorrect. AOX accepts electrons from ubiquinol (the reduced form of ubiquinone) rather than cytochrome c, which is part of the classical electron transport chain.
(2) Some plants exhibit thermogenesis during inflorescence development.
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Correct. Plants like Saummatum guttatum generate heat in their inflorescences by upregulating AOX activity to attract pollinators.
(3) Transcription of alternate oxidase gene is often induced by various abiotic stresses.
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Correct. AOX gene expression increases under stresses like cold, drought, and pathogen attack to modulate ROS and maintain respiration.
(4) When electrons pass to alternate oxidase, two sites of proton pumping are bypassed.
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Correct. AOX allows electrons to bypass complexes III and IV, reducing ATP synthesis efficiency but avoiding excess reactive oxygen species.
Why Option (1) Is Not Correct
AOX’s true electron donor is ubiquinol, not cytochrome c. This distinction is crucial for understanding its role in the mitochondrial electron transport chain and its contribution to alternative respiration.
This knowledge is essential for plant biology students and researchers focusing on bioenergetics and stress physiology.
