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This research first verified that prokaryotic algae are more sensitive to toxicity of CuO nanoparticles (CuO NPs) than eukaryotic algae and that CuO NPs damaged photosynthesis of prokaryotic algae (Arthrospira sp.) but had no effect on respiration. The Cu2+ released by CuO NPs caused a bending deformation of the thylakoid, which was an important cause of the decline in photosynthetic capacity. In addition, the D1 protein was the most susceptible site to CuO NPs. The degradation of D1 protein reduced photosynthetic electron transport, which enhanced the excess excitation energy to cause the accumulation of reactive oxygen species (ROS) to further result in oxidative stress on algae. Dissolved organic matter (DOM) increased the toxicity of CuO NPs to photosynthesis of Arthrospira sp. The damage of photosynthesis caused by CuO NPs is an important reason why CuO NPs have a serious toxicity to algae. [ABSTRACT FROM AUTHOR]

Highlights • The link between biochemical factors and programmed cell death and scald severity is unknown. • Changes in these factors at various temperatures and durations were studied. • During low-temperature storage, scald developed quickly. • Scald increases in proportion with storage time. • Scald is closely associated with conjugated trienols and programmed cell death. Abstract Superficial scald is a physiological disorder affecting apple fruit during cold storage. Previous studies have reported that multiple factors, such as α-farnesene, ethylene, conjugated trienols (CTols), reactive oxygen species (ROS), and programmed cell death (PCD) are associated with superficial scald. However, the correlation between the factors and scald severity under different storage durations has rarely been reported. In this study, we analyzed how these factors change over time (0 d, 7 d, 30 d, 60 d and 90 d) in association with the incidence of scald in 'White Winter Pearmain' apples at low-temperature (5 °C). The results showed that the time for scald to development is short and the incidence of scald increases with storage time. The highest level of α-farnesene was observed after 7 d, whereas, the production rate of CTols, O 2 −, H 2 O 2, and ethylene gradually increased with time. In addition, specific expression profiling of MdDAD1 , MdLSD1 and MdDND1 suggested that PCD was involved with scald development. The correlation analysis showed that content of CTols, the production rate of ethylene, and the expression of MdAFS , MdHMGR2 , MdACS1 , MdACO1 , MdDAD1 , and MdLSD1 were strongly associated with superficial scald, whereas, α-farnesene and ROS were weakly associated. These results suggest that CTols and PCD are associated with scald development and that their role is more prominent than ROS. This is a novel perspective on the cause of scald that-can help develop potential solutions to inhibit scald development. [ABSTRACT FROM AUTHOR]

Little is known regarding the detailed mechanism of CuO NPs' toxicity to microalgal primary metabolism pathway. Photosynthesis and respiration are the most important primary metabolism and the main sources of production of reactive oxygen species (ROS), but the effect of CuO NPs on both of them has not been systematically studied to date. Our research demonstrated that long-term treatment with CuO NPs significantly inhibited activities of photosynthesis and respiration in microalgae, and the photosynthesis was more sensitive to the toxicity of CuO NPs than respiration. CuO NPs could be absorbed by microalgae and be converted into Cu2O NPs concentrated in chloroplast. The internalized Cu, regardless of whether the exposure was Cu2+ or CuO NPs had the same capacity to damage chloroplast structure. The result also shows that the oxygen-evolving complex (OEC) in the photosynthetic electron transport chain was the most sensitive site to CuO NPs and Cu2+-treated microalgae had the same damage site as that of CuO NPs, which may be related to the Mn cluster that is dissociated by Cu ions released from CuO NPs. The damage of OEC inhibited photosynthetic electron transport to increase excess excited energy, which caused the accumulation of ROS in chloroplast. The accumulation of ROS damaged the structure of cell membrane and aggravated the PSII photoinhibition, further decreasing the efficiency of light energy utilization. In conclusion, the Cu ionic toxicity of photosynthetic apparatus by CuO NPs resulted in the carbon starvation and the accumulation of ROS to inhibit the growth of microalgae. [ABSTRACT FROM AUTHOR]