The potential for exposure to fluctuating light has necessitated that plants evolve protective mechanisms for when the light intensity exceeds photosynthetic capacity. Under these conditions, reactive oxygen species cause photoinhibition, which hinders photosynthetic efficiency. To counter this loss in photosynthetic efficiency, chloroplasts evolved thioredoxin (Trx) proteins that regulate redox balance within the photosynthetic apparatus and provide a photoprotective function.
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Source: Phys.org