Pyridinic Nitrogen Doped Carbon Dots Supply Electrons to Improve Photosynthesis and Extracellular Electron Transfer of Chlorella pyrenoidosa.

Optimizing photosynthesis is imperative for providing energy and organics for all life on the earth. Here, carbon dots doped with pyridinic nitrogen (named lev-CDs) are synthesized by the one-pot hydrothermal method, and the structure-function relationship between functional groups on lev-CDs and photosynthesis of Chlorella pyrenoidosa (C. pyrenoidosa) is proposed. Pyridinic nitrogen plays a key role in the positive effect on photosynthesis caused by lev-CDs. In detail, lev-CDs act as electron donors to supply photo-induced electrons to P680+ and QA+ , causing electron transfer from lev-CDs to the photosynthetic electron transport chain in the photosystems. In return, the recombination efficiency of electron-hole pairs on lev-CDs decreases. As a result, the electron transfer rate in the electron transport chain, the activity of photosystem II, and the Calvin cycle are enhanced. Moreover, the electron transfer rate between C. pyrenoidosa and external circumstances enhanced by lev-CDs is about 50%, and electrons exported from C. pyrenoidosa can be used to reduce iron(III). This study is of great significance for engineering nanomaterials to improve photosynthesis.

Carbon dot based sensing platform for real-time imaging Cu2+ distribution in plants and environment.

Divalent copper is a double-edged sword for plants, excess or shortage of copper ions will cause adverse reactions in plants. Currently, Cu2+ sensor for plants is still underdeveloped and new technology is urgently required for realizing one-step and real-time detection of Cu2+ in plants. Herein, a home-made and low-cost sensing platform is constructed by using carbon dots (CDs) as the optical probe, electronic devices for image acquisition, and a built-in algorithm program for image processing, which allows the dynamic monitoring of Cu2+ distribution in different plant species with high spatial and temporal resolution. We found that the detection limit of R-CDs for Cu2+ in water sample was 0.375 nM, and 11.7 mg/kg or even less Cu2+ in plants can be visually observed and accurately detected by the sensing platform. Moreover, this sensing platform has also been employed for reporting the spatial distribution of Cu2+ in the external environment of plants, demonstrating its applicability for monitoring Cu2+ both in living plants and the surrounding environment. This study provides a smart sensing platform for precise detection in plant internal and external environments, offering a promising strategy for precision agriculture in real-time and remote-control manners.

Dose-Dependent Effect of ZnO Quantum Dots for Lettuce Growth.

As the cadmium-free semiconductor quantum dots, ZnO quantum dots (ZnO QDs) have wide potential applications in agriculture. However, the effects of ZnO quantum dots on crop growth and nutritional quality have not been fully studied. In this work, the lettuce was sprayed with different concentrations of ZnO QDs from 50 to 500 mg·L-1 to evaluate their influence on lettuce antioxidant, biomass, and nutritional quality. The results showed that ZnO QDs existed in the lettuce in the form of Zn2+. Lettuce treated with 500 mg·L-1 ZnO QDs would produce a large amount of reactive oxygen species (ROS), which adversely affected the absorption of nutrients, soluble protein content, and chlorophyll content, thus reducing plant biomass. When the concentrations range from 50 to 200 mg·L-1, the antioxidant enzyme systems of lettuce were triggered to counteract the damage caused by excessive ROS. Moreover, ZnO QDs at this level promoted Ca, Mg, Fe, Mn, Zn, and B absorption and accumulation; increased soluble sugar content; and improved the lettuce biomass and nutritional quality.

Crosstalk between auxin and gibberellin during stalk elongation in flowering Chinese cabbage.

Plant growth and development are tightly regulated by phytohormones. However, little is known about the interaction between auxin and gibberellin acid (GA) during flower stalk elongation and how it is directly related to organ formation. Therefore, the effects of indole acetic acid (IAA) and GA3 treatments and their interaction on flower stalk elongation in flowering Chinese cabbage were investigated. The growth of flowering Chinese cabbage is regulated by IAA and GA3, and the opposite results were observed after treatments with uniconazole (GA synthesis inhibitor) and N-1-naphthylphthalamic acid (NPA) (auxin transport inhibitor). Anatomical analysis of the pith region in stalks revealed that IAA promoted expansion via signal transduction and transport pathways. GA3 regulated the elongation of flower stalks by controlling GA synthesis and partially controlling the IAA signaling pathway. GA3 also had a stronger effect on stalk elongation than IAA. The results of qRT-PCR and histological analysis revealed that GA3 and IAA induced the expansion of cell walls by activating the expression of genes encoding cell wall structural proteins such as Expansin (EXP). These findings provide new insights into the mechanism of stalk formation regulated by the combination of IAA and GA3.

Nitrogen and Sulfur Co-doped Carbon Dots Enhance Drought Resistance in Tomato and Mung Beans.

Drought stress is widespread worldwide, which severely restricts world food production. The antioxidant property of carbon dots (CDs) is promising for inflammation and disease treatment. However, little is known about the functions of CDs in the abiotic stress of plants, especially in drought-resistant fields. In this study, CDs were synthesized using cysteine and glucose by the hydrothermal method. The in vitro antioxidant capacity of CDs and the reactive oxygen species (ROS) scavenging capacity were evaluated. We speculate on the antioxidant mechanism of CDs by comparing size distribution, fluorescence spectra, elements, and surface functional groups of CDs before and after oxidation. Besides, we evaluated the effects of CDs on seed germination and seedling physiology under drought stress. Also, the responses of antioxidant CDs to long-term drought stress and subsequent recovery metabolism in tomato plants were evaluated. The results show that CDs accelerated the germination rate and the germination drought resistance index by promoting the water absorption of seeds. CDs enhanced the drought resistance of seedlings by improving the activity of peroxidase (POD) and superoxide dismutase (SOD). Moreover, CDs can activate the antioxidant metabolism activity and upregulate the expression of aquaporin (AQP) genes SlPIP2;7, SlPIP2;12, and SlPIP1;7. All of these results render tomato plants distinguished resilience once rewatering after drought stress. These results facilitate us to design and fabricate CDs to meet the challenge of abiotic stress in food production.