Flavodiiron-mediated O2 photoreduction at photosystem I acceptor-side provides photoprotection to conifer thylakoids in early spring

Generally, net O-2 consumption becomes dominant when photosynthesis is suppressed at night in green organisms. Here, Bag et al. show that Scots pine and Norway spruce needles display strong O-2 consumption when extremely low temperatures coincide with high solar irradiation during early spring. Green organisms evolve oxygen (O-2) via photosynthesis and consume it by respiration. Generally, net O-2 consumption only becomes dominant when photosynthesis is suppressed at night. Here, we show that green thylakoid membranes of Scots pine (Pinus sylvestris L) and Norway spruce (Picea abies) needles display strong O-2 consumption even in the presence of light when extremely low temperatures coincide with high solar irradiation during early spring (ES). By employing different electron transport chain inhibitors, we show that this unusual light-induced O-2 consumption occurs around photosystem (PS) I and correlates with higher abundance of flavodiiron (Flv) A protein in ES thylakoids. With P700 absorption changes, we demonstrate that electron scavenging from the acceptor-side of PSI via O-2 photoreduction is a major alternative pathway in ES. This photoprotection mechanism in vascular plants indicates that conifers have developed an adaptative evolution trajectory for growing in harsh environments.

Automated summary

This study reveals that Scots pine and Norway spruce needles exhibit strong oxygen consumption during early spring when extremely low temperatures coincide with high solar irradiation. The light-induced oxygen consumption occurs around photosystem I and is correlated with the abundance of flavodiiron A protein. This photoprotection mechanism suggests that conifers have evolved to adapt to harsh environments.