Analysis of the changes of electron transfer and heterogeneity of photosystem II in Deg1-reduced Arabidopsis plants

The photosystem-II repair cycle: updates and open questions

MAIN CONCLUSION

The photosystem-II (PSII) repair cycle is essential for the maintenance of photosynthesis in plants. A number of novel findings have illuminated the regulatory mechanisms of the PSII repair cycle. Photosystem II (PSII) is a large pigment-protein complex embedded in the thylakoid membrane. It plays a vital role in photosynthesis by absorbing light energy, splitting water, releasing molecular oxygen, and transferring electrons for plastoquinone reduction. However, PSII, especially the PsbA (D1) core subunit, is highly susceptible to oxidative damage. To prevent irreversible damage, plants have developed a repair cycle. The main objective of the PSII repair cycle is the degradation of photodamaged D1 and insertion of newly synthesized D1 into the PSII complex. While many factors are known to be involved in PSII repair, the exact mechanism is still under investigation. In this review, we discuss the primary steps of PSII repair, focusing on the proteolytic degradation of photodamaged D1 and the factors involved.

StLTO1, a lumen thiol oxidoreductase in Solanum tuberosum L., enhances the cold resistance of potato plants

Cold stress reduces plant photosynthesis and increases the accumulation of reactive oxygen species (ROS) in plants, thereby dramatically affecting plant growth, crop productivity and quality. Here, we report that lumen thiol oxidoreductase 1 (StLTO1), a vitamin K epoxide reductase (VKOR)-like protein in the thylakoid membrane of Solanum tuberosum L., enhances the cold tolerance of potato plants. Under normal conditions, overexpression of StLTO1 in plants promoted plant growth. In addition, potato plants overexpressing StLTO1 displayed enhanced photosynthetic capacity and increased capacity for scavenging ROS compared to StLTO1 knockdown and wild-type potato plants under cold conditions. Overexpression of StLTO1 in potato plants also improved cold-regulated (COR) gene expression after cold stress. Our results suggest that StLTO1 acts as a positive regulator of cold resistance in potato plants.

Metamitron, a Photosynthetic Electron Transport Chain Inhibitor, Modulates the Photoprotective Mechanism of Apple Trees

Chemical thinning of apple fruitlets is an important practice as it reduces the natural fruit load and, therefore, increases the size of the final fruit for commercial markets. In apples, one chemical thinner used is Metamitron, which is sold as the commercial product Brevis^® (Adama, Ashdod, Israel). This thinner inhibits the electron transfer between Photosystem II and Quinone-b within light reactions of photosynthesis. In this study, we investigated the responses of two apple cultivars-Golden Delicious and Top Red-and photosynthetic light reactions after administration of Brevis^®. The analysis revealed that the presence of the inhibitor affects both cultivars' energetic status. The kinetics of the photoprotective mechanism's sub-processes are attenuated in both cultivars, but this seems more severe in the Top Red cultivar. State transitions of the antenna and Photosystem II repair cycle are decreased substantially when the Metamitron concentration is above 0.6% in the Top Red cultivar but not in the Golden Delicious cultivar. These attenuations result from a biased absorbed energy distribution between photochemistry and photoprotection pathways in the two cultivars. We suggest that Metamitron inadvertently interacts with photoprotective mechanism-related enzymes in chloroplasts of apple tree leaves. Specifically, we hypothesize that it may interact with the kinases responsible for the induction of state transitions and the Photosystem II repair cycle.