Simultaneous determination of coenzyme Q and plastoquinone redox states in the coral–Symbiodinium symbiosis during thermally induced bleaching

Coenzyme Q (CoQ; ubiquinone) and plastoquinone (PQ) are metabolic electron carriers that, in their reduced state, are powerful antioxidants for cellular protection against oxidative damage. Although damage resulting from generation of reactive oxygen species (ROS) is strongly implicated in the initiation of symbiotic dysfunction that leads to coral bleaching, very little is known about the redox state of these two prenylquinone pools during the stress response. Here we describe a quantitative liquid chromatography–mass spectrometry (LC–MS) method that permits simultaneous measurement of the physiological redox state of both CoQ and PQ in whole corals. The application of this method indicates that the CoQ and PQ pools in the coral–Symbiodinium symbiosis are maintained predominantly in their reduced (antioxidant) forms, and it is the coral CoQ redox state that is most affected by acute thermal stress.