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Abstract
High light intensities raise photosynthetic and plant growth rates but can cause damage to the photosynthetic machinery. The likelihood and severity of deleterious effects are minimised by a set of photoprotective mechanisms, one key process being the controlled dissipation of energy from chlorophyll within PSII known as non-photochemical quenching (NPQ). Although ubiquitous, the role of NPQ in plant productivity is important because it momentarily reduces the quantum efficiency of photosynthesis. Rice plants overexpressing and deficient in the gene encoding a central regulator of NPQ, the protein PsbS, were used to assess the effect of protective effectiveness of NPQ (pNPQ) at the canopy scale. Using a combination of three-dimensional reconstruction, modelling, chlorophyll fluorescence, and gas exchange, the influence of altered NPQ capacity on the distribution of pNPQ was explored. A higher phototolerance in the lower layers of a canopy was found, regardless of genotype, suggesting a mechanism for increased protection for leaves that experience relatively low light intensities interspersed with brief periods of high light. Relative to wild-type plants, psbS overexpressors have a reduced risk of photoinactivation and early growth advantage, demonstrating that manipulating photoprotective mechanisms can impact both subcellular mechanisms and whole-canopy function.
Highlights
Photosynthetic efficiency is a limitation to achieving the increases in crop productivity needed to meet the demands of an expanding population
The likelihood and severity of deleterious effects are minimised by a set of photoprotective mechanisms, one key process being the controlled dissipation of energy from chlorophyll within PSII known as non-photochemical quenching (NPQ)
The fastest component of NPQ is qE, or energy-dependent quenching, and is triggered by the generation of a pH gradient across the thylakoid membrane (Krause, 1974; Horton et al, 2005; Zulfugarov et al, 2007). qE is known to be modulated by the carotenoid zeaxanthin and the protein PSII subunit S (PsbS), which act as allosteric regulators to alter the structure of the membrane and antenna conformation in order to enhance the affinity for protons, facilitating qE formation and relaxation (Niyogi et al, 2005; Johnson and Ruban, 2010, 2011; Kereïche et al, 2010; Murchie and Niyogi, 2011; Goral et al, 2012; Harbinson, 2012; Roach and Krieger-Liszkay, 2012; Ruban, 2012, 2016, 2017; Zaks et al, 2012; Sacharz et al, 2017)
Summary
Photosynthetic efficiency is a limitation to achieving the increases in crop productivity needed to meet the demands of an expanding population. We lack an understanding of how canopy structure and internal biochemistry combine to determine the absorption and utilization of light, within the field setting.The within-canopy light environment is highly dynamic, with up to a 50-fold difference in light intensity reaching leaves at the top of the canopy compared with those at the bottom (Niinemets and Keenan, 2012).This is further confounded by changes in canopy architecture, such The fastest component of NPQ is qE, or energy-dependent quenching, and is triggered by the generation of a pH gradient across the thylakoid membrane (Krause, 1974; Horton et al, 2005; Zulfugarov et al, 2007). qE is known to be modulated by the carotenoid zeaxanthin and the protein PSII subunit S (PsbS), which act as allosteric regulators to alter the structure of the membrane and antenna conformation in order to enhance the affinity for protons, facilitating qE formation and relaxation (Niyogi et al, 2005; Johnson and Ruban, 2010, 2011; Kereïche et al, 2010; Murchie and Niyogi, 2011; Goral et al, 2012; Harbinson, 2012; Roach and Krieger-Liszkay, 2012; Ruban, 2012, 2016, 2017; Zaks et al, 2012; Sacharz et al, 2017)
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