Abstract
Light is the driving force of plant growth, providing the energy required for photosynthesis. However, photosynthesis is also vulnerable to light-induced damage caused by the production of reactive oxygen species (ROS). Plants have therefore evolved various protective mechanisms such as non-photochemical quenching (NPQ) to dissipate excessively absorbed solar energy as heat; however, photoinhibition and NPQ represent a significant loss in solar energy and photosynthetic efficiency, which lowers the yield potential in crops. To estimate light capture and light energy conversion in rice, a genotype with pale green leaves (pgl) and a normally pigmented control (Z802) were subjected to high (HL) and low light (LL). Chlorophyll content, light absorption, chloroplast micrographs, abundance of light-harvesting complex (LHC) binding proteins, electron transport rates (ETR), photochemical and non-photochemical quenching, and generation of ROS were subsequently examined. Pgl had a smaller size of light-harvesting chlorophyll antenna and absorbed less photons than Z802. NPQ and the generation of ROS were also low, while photosystem II efficiency and ETR were high, resulting in improved photosynthesis and less photoinhibition in pgl than Z802. Chlorophyll synthesis and solar conversion efficiency were higher in pgl under HL compared to LL treatment, while Z802 showed an opposite trend due to the high level of photoinhibition under HL. In Z802, excessive absorption of solar energy not only increased the generation of ROS and NPQ, but also exacerbated the effects of increases in temperature, causing midday depression in photosynthesis. These results suggest that photosynthesis and yield potential in rice could be enhanced by truncated light-harvesting chlorophyll antenna size.
Highlights
Global agriculture is facing unprecedented challenges, with a predicted increase in primary foodstuffs of 85% required by 2050, relative to 2013 (Ray et al, 2013)
Compared with low light (LL) treatment, the chlorophyll content of Zhefu 802 (Z802) decreased by 22% under HL
The ratio of chlorophyll a to b (Chl a/b) were greatly improved absorptance was comparable between LL and HL treatment, with leaves adapted to LL absorbing more photons than those adapted to HL
Summary
Global agriculture is facing unprecedented challenges, with a predicted increase in primary foodstuffs of 85% required by 2050, relative to 2013 (Ray et al, 2013). To protect PSII from excess radiation, plants dissipate excessive energy as heat via the xanthophyll cycle, which involves de-epoxidase-induced catalysis of the xanthophyll pigment violaxanthin to zeaxanthin This photoprotection process is referred to as NPQ of chlorophyll fluorescence (Niyogi et al, 1998; Miyake et al, 2005; Yamori and Shikanai, 2016), and represents a significant loss of solar energy (Ort et al, 2015). If plants had fewer light-harvesting pigments (e.g., chlorophyll and carotenoids) per photosystem, solar energy conversion efficiency could be greatly improved (Melis, 2009; Ort et al, 2011, 2015; Long et al, 2015). The results would provide valuable insight into the mechanisms of photoprotection and increased photosynthetic efficiency with truncated light-harvesting chlorophyll antenna size, helping development of strategies for improved grain yield potential in rice
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