Photorespiration does not act as a photoprotective electron sink under unstressed conditions.

Fractional metabolic poise toward photorespiration is the largest determinant of long-lived downregulation of light harvesting at photosystem II, but this downregulation does not correlate with D1 loss.

• Why it matters: The work addresses whether photorespiration functions as a photoprotective electron sink that prevents electron-transport damage and preserves photosystem II activity under unstressed conditions.
• What they did: Using chlorophyll a fluorescence coupled to gas exchange, the authors probed electron-transport responses across a wide range of metabolic poise controlled by O2 and CO2 gas mixing.
• The result: The observed long-lived downregulation is linked to photorespiratory metabolic poise rather than D1 loss, contradicting a photoprotective electron-sink role and showing that O2 also affects downregulation independently of metabolic poise.

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