Instantaneous switching between different modes of non-photochemical quenching in plants. Consequences for increasing...

Photosynthetic productivity usually saturates far below the maximum solar light intensity, meaning that in those conditions many absorbed photons and the resulting electronic excitations of the pigment molecules can no longer be utilized for photosynthesis. To avoid photodamage, various protection mechanisms are induced that dissipate excess excitations, which otherwise could lead to the formation of harmful molecular species like singlet oxygen. This Non-Photochemical Quenching (NPQ) of excitations can be monitored via a decrease of the chlorophyll fluorescence. There is consensus that in plants 1) there are at least two major NPQ (sub)processes and 2) NPQ (de)activation occurs on various time scales, ranging from (tens of) seconds to minutes. This relatively slow switching has a negative effect on photosynthetic efficiency, and Kromdijk et al. demonstrated in 2016 (Science 354, 857) that faster switching rates can lead to increased crop productivity. Very recently, we were involved in the discovery of a new NPQ process that switches off well within a millisecond (Farooq et al. (2018) Nat. Plants 4, 225). Here we describe the current level of knowledge regarding this process and discuss its implications.