Carbon Dots and Single-walled Carbon Nanotubes Enhances Maize Shading Stress Tolerance

Low sunlight availability/shading stress is one of the major abiotic stresses, limiting plant photosynthesis and biomass production. Maize is a C4 species and requires more sunshine for efficient photosynthesis rate. Thus, maize is a highly shade-sensitive species. We used carbon dots (CDs) and single-walled carbon nanotubes (SWCNTs) as a foliar application to enhance maize photosynthesis under no-shading and shading stress. The results revealed that under shading stress, the higher concentration of CDs and SWCNTs reduced the MDA (Malondialdehyde) content and increased the expression level of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) genes. Moreover, under shading stress, CDs and SWCNTs increased the average thickness of leaf lamina, vascular bundle, mesophyll, and epidermis. CDs and SWCNTs reduced the damaging effects of shading stress on the chloroplast (Ch) formation. CDs and SWCNTs upregulated Rubisco and related genes under shading stress. The chlorophyll fluorescence parameters, including the efficiency of quantum yield of photosystem II (Fv/Fm), electron transport rate (ETR), non-photochemical quenching coefficient (NPQ), and photochemical quenching coefficient (qP) were improved with the foliar application of CDs and SWCNTs under shading stress. Higher stomatal conductance, intercellular CO2 concentration, transpiration, and net photosynthesis were observed in maize plants treated with CDs and SWCNTs under shading stress. The results of our study suggest that using higher concentrations of CDs and SWCNTs can enhance plant growth and photosynthesis under shading stress conditions. However, to avoid nanotoxicity, great care is recommended when selecting different concentrations of nanomaterials based on the growing conditions.