Abstract
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).
Highlights
To add to the above, high light can be potentially deleterious
This rather dull name belies an elegant and fascinating mechanism, ubiquitous among plants, that regulates the level of excitation within the pigment bed of the thylakoid membrane and partly determines the amount of excitation energy available for photosynthesis (Horton et al 1996; Demmig-Adams et al 2014)
With NPQ at zero, light energy absorbed by chlorophyll within Light Harvesting Complexes (LHC) is transferred efficiently to reaction centres via resonance transfer, and the quantum yield of photosynthesis is at a maximum (Fig. 1)
Summary
To add to the above, high light can be potentially deleterious. Light energy that is harvested by chlorophyll in the Light Harvesting Complexes (LHC) of photosystem II (PSII) is used by the reaction centres of PSII to split water via the oxygen evolving complex, using the resultant electrons and protons in the thylakoid membrane to generate ATP and reducing power for CO2 assimilation. One of the most well studied is the controlled dissipation of excitation energy from chlorophyll which is measured as nonphotochemical quenching or NPQ. With NPQ at zero, light energy absorbed by chlorophyll within LHCs is transferred efficiently to reaction centres via resonance transfer, and the quantum yield of photosynthesis is at a maximum (Fig. 1).
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