Safety conscious or living dangerously: what is the ‘right’ level of plant photoprotection for fitness and productivity?

Due to their sessile nature, plants could be perceived to be relatively slow and rather un-reactive. However, a plant scientist will tell you that the inability to run away (tropism notwithstanding) actually demands a highly sophisticated physiological response to the environment. Light presents an extreme case: cloud cover and wind-induced motion can lead to irradiance changes of several orders of magnitude over timescales of seconds and minutes. Being autotrophic organisms and having evolved to harvest light, plants need to dynamically regulate their biochemistry so that it operates efficiently during these fluxes, maintaining plant fitness but minimising the risk of damage.Photosynthesis is driven at a rate that depends on the amount of available light, as shown by the schematic photosynthesis-light response curves of C3 species (Fig. 1). In nature, CO2 assimilation can go from being light-limited to being light-saturated within a very short period of time. To maximise CO2 uptake, photosynthesis should ‘track’ light levels accurately inducing and removing photoprotective processes accurately. Being able to measure photoprotection precisely in naturally fluctuating settings is difficult; however, a paper in this volume of Plant, Cell and Environment proposes a significant advance (Tietz et al. 2017).