Is electron transport to oxygen an important mechanism in photoprotection? Contrasting responses from Antarctic vascular plants

Photoreduction of oxygen by the photosynthetic electron transport chain has been suggested to be an important process in protecting leaves from excess light under conditions of stress; however, there is little evidence that this process occurs significantly except when plants are exposed to conditions outside their normal tolerance range. We have examined the oxygen dependency of photosynthetic electron transport in the two vascular plants found growing in Antarctica - Colobanthus quitensis and Deschampsia antarctica. Photosynthetic electron transport in C. quitensis is insensitive to changes in oxygen concentration under non-photorespiratory conditions, indicating that electron transport to oxygen is negligible; however, it has a substantial capacity for non-photochemical quenching (NPQ) of chlorophyll fluorescence. In contrast, D. antarctica has up to 30% of its photosynthetic electron transport being linked to oxygen, but has a substantially lower capacity for NPQ. Thus, these plants rely on contrasting photoprotective mechanisms to cope with the Antarctic environment. Both plants seem to use cyclic electron flow associated with PSI, however, this is activated at a lower irradiance in C. quitensis than in D. antarctica.