Graphene Oxide, a Novel Nanomaterial as Soil Water Retention Agent, Dramatically Enhances Drought Stress Tolerance in Soybean Plants

Research Progress and Prospects of Nanozymes in Alleviating Abiotic Stress of Crops

The continuous destruction of the global ecological environment has led to increased natural disasters and adverse weather, severely affecting crop yields and quality, particularly due to abiotic stress. Nanase, a novel artificial enzyme, simulates various enzyme activities, is renewable, and shows significant potential in promoting crop growth and mitigating abiotic stress. This study reviews the classification of nanoenzymes into carbon-based, metal-based, metal oxide-based, and others based on synthesis materials. The catalytic mechanisms of these nanoenzymes are discussed, encompassing activities, such as oxidases, peroxidases, catalases, and superoxide dismutases. The catalytic mechanisms of nanoenzymes in alleviating salt, drought, high-temperature, low-temperature, heavy metal, and other abiotic stresses in crops are also highlighted. Furthermore, the challenges faced by nanoenzymes are discussed, especially in sustainable agricultural development. This review provides insights into applying nanoenzymes in sustainable agriculture and offers theoretical guidance for mitigating abiotic stress in crops.

Metabolomic analyses reveal that graphene oxide alleviates nicosulfuron toxicity in sweet corn

Nicosulfuron can repress the growth and quality of sweet corn (Zea mays), and graphene oxide has been used for sustainable agriculture. However, the underlying mechanism of the toxicity of nicosulfuron that is mediated in sweet corn remains elusive. To explore the potential mechanism of GO-mediated nicosulfuron toxicity in sweet corn in this study, we investigated the effects of graphene oxide on nicosulfuron stress in the sweet corn sister inbred lines of H01 and H20. Furthermore, we performed a metabolomics analysis for the H01 and H20 under different treatments. The results showed that nicosulfuron severely affected the rate of survival, physiological parameters, photosynthetic indicators, and chlorophyll fluorescence parameters of corn seedlings, whereas foliar spraying with graphene oxide promoted the rate of survival under nicosulfuron toxicity. The metabolomics analysis showed that 70 and 90 metabolites differentially accumulated in the H01 and H20 inbred lines under nicosulfuron treatment, respectively. Graphene oxide restored 59 metabolites in the H01 seedlings and 56 metabolites to normal levels in the H20 seedlings, thereby promoting the rate of survival of the sweet corn seedlings. Compared with nicosulfuron treatment alone, graphene oxide resulted in 108 and 66 differential metabolites in the H01 and H20 inbred lines, respectively. A correlation analysis revealed that metabolites, such as doronine and (R)-2-hydroxy-2-hydroxylase-1,4-benzoxazin-3(4-hydroxylase)-1, were significantly correlated with the rate of survival, photosynthetic parameters and chlorophyll fluorescence parameters. Furthermore, metabolites related to the detoxification of graphene oxide were enriched in the flavonoid metabolic pathways. These results collectively indicate that graphene oxide can be used as a regulator of corn growth and provide insights into their use to improve crops in areas that are contaminated with nicosulfuron.

Carbon Nanomaterials in Seed Priming: Current Possibilities

The prevailing agricultural system has become deeply ingrained and insufficient due to outdated practices inherited from the Green Revolution, necessitating innovative approaches for sustainable agricultural development. Nanomaterials possess the potential to significantly improve the efficient utilization of resources while simultaneously encouraging sustainability. Among these, carbonaceous nanomaterials have found diverse applications in agriculture, exhibiting remarkable capabilities in this domain. Notably, using biowaste to produce these materials makes them both cost-effective and environmentally friendly for seed priming. Seed priming is a technique that can potentially enhance germination rates and stress tolerance by effectively regulating gene pathways and metabolism. This review provides a comprehensive summary of recent progress in the field, highlighting the challenges and opportunities of applying carbonaceous materials in seed priming to advance sustainable agriculture practices. The existing reviews provide a general overview of using carbonaceous materials (graphene and derivatives) in agriculture. Yet, they often lack a comprehensive examination of their specific application in seed-related contexts. In this review, we aim to offer a detailed analysis of the application of carbonaceous materials in seed priming and elucidate their influence on germination. Furthermore, the review shows that crop response to carbonaceous nanomaterials is linked to material concentration and crop species.

The impact of single and combined amendment of elemental sulphur and graphene oxide on soil microbiome and nutrient transformation activities

Background

Sulphur (S) deficiency has emerged in recent years in European soils due to the decreased occurrence of acid rains. Elemental sulphur (S0) is highly beneficial as a source of S in agriculture, but it must be oxidized to a plant-accessible form. Micro- or nano-formulated S0 may undergo accelerated transformation, as the oxidation rate of S0 indirectly depends on particle size. Graphene oxide (GO) is a 2D-carbon-based nanomaterial with benefits as soil amendment, which could modulate the processes of S0 oxidation. Micro-and nano-sized composites, comprised of S0 and GO, were tested as soil amendments in a pot experiment with unplanted soil to assess their effects on soil microbial biomass, activity, and transformation to sulphates. Fourteen different variants were tested, based on solely added GO, solely added micro- or nano-sized S0 (each in three different doses) and on a combination of all S0 doses with GO.

Results

Compared to unamended soil, nano-S0 and nano-S0+GO increased soil pH(CaCl2). Micro-S0 (at a dose 4 g kg-1) increased soil pH(CaCl2), whereas micro-S0+GO (at a dose 4 g kg-1) decreased soil pH(CaCl2). The total bacterial and ammonium oxidizer microbial abundance decreased due to micro-S0 and nano-S0 amendment, with an indirect dependence on the amended dose. This trend was alleviated by the co-application of GO. Urease activity showed a distinct response to micro-S0+GO (decreased value) and nano-S0+GO amendment (increased value). Arylsulfatase was enhanced by micro-S0+GO, while sulphur reducing bacteria (dsr) increased proliferation due to high micro-S0 and nano-S0, and co-amendment of both with GO. In comparison to nano-S0, the amendment of micro-S0+GO more increased soluble sulphur content more significantly.

Conclusions

Under the conditions of this soil experiment, graphene oxide exhibited a significant effect on the process of sulphur oxidation.

Effect of graphene on soybean root colonization by Bradyrhizobium strains

Legume crops such as soybean obtain a large portion of their nitrogen nutrition through symbiotic nitrogen fixation by diazotrophic rhizobia bacteria in root nodules. However, nodule occupancy by low-capacity nitrogen-fixing rhizobia can lead to lower-than-optimal levels of nitrogen fixation. Seed/root coating with engineered materials such as graphene-carrying biomolecules that may promote specific attraction/attachment of desirable bacterial strains is a potential strategy that can help overcome this rhizobia competition problem. As a first step towards this goal, we assessed the impact of graphene on soybean and Bradyrhizobium using a set of growth, biochemical, and physiological assays. Three different concentrations of graphene were tested for toxicity in soybean (50, 250, and 1,000 mg/l) and Bradyrhizobia (25, 50, and 100 mg/l). Higher graphene concentrations (250 mg/l and 1,000 mg/l) promoted seed germination but slightly delayed plant development. Spectrometric and microscopy assays for hydrogen peroxide and superoxide anion suggested that specific concentrations of graphene led to higher levels of reactive oxygen species in the roots. In agreement, these roots also showed higher activities of antioxidant enzymes, catalase, and ascorbate peroxidase. Conversely, no toxic effects were detected on Bradyrhizobia treated with graphene, and neither did they have higher levels of reactive oxygen species. Graphene treatments at 250 mg/l and 1,000 mg/l significantly reduced the number of nodules, but rhizobia infection and the overall nitrogenase activity were not affected. Our results show that graphene can be used as a potential vehicle for seed/root treatment.

Unveiling the Effects of Carbon-Based Nanomaterials on Crop Growth: From Benefits to Detriments

To systematically assess the impact of typical CNMs on the growth effects of cereal crops, we conducted a meta-analysis of 48 independent studies worldwide. The pooled results showed that shoot weight (13.39%) and antioxidant metabolite content (SOD: 106.32%, POD: 32.29%, CAT: 22.63%) of cereal crops exposed to the presence of CNMs were significantly increased, but phytohormones secretion (17.84%) was inhibited. The results of subgroup analysis showed that there were differences in the results of different CNM types with the same exposure concentration on growth effects. Short-term exposure adversely affected the root and photosynthetic capacity of the crop, but prolonged exposure instead showed a promoting effect. Multiple linear regression analysis showed that the concentration of CNMs and cereal variety variables were significantly associated with changes in multiple growth effect values. This work could offer references and fresh perspectives for investigating how nanoparticles and crops interact.

How Scarification, GA3 and Graphene Oxide Influence the In Vitro Establishment and Development of Strelitzia

The propagation of strelitzia plants can be carried out in vitro as an alternative to combine the aseptic conditions of the culture medium with the use of strategies to promote germination and controlled abiotic conditions. However, this technique is still limited by the prolonged time and low percentage of seed germination, which is the most viable explant source, due to dormancy. Thus, the objective of this study was to evaluate the influence of chemical and physical scarification processes of seeds combined with gibberellic acid (GA₃), as well as the effect of graphene oxide in the in vitro cultivation of strelitzia plants. Seeds were subjected to chemical scarification with sulfuric acid for different periods (10 to 60 min) and physical scarification (sandpaper), in addition to a control treatment without scarification. After disinfection, the seeds were inoculated in MS (Murashige and Skoog) medium with 30 g L^-1 sucrose, 0.4 g L^-1 PVPP (polyvinylpyrrolidone), 2.5 g L^-1 Phytagel^®, and GA₃ at different concentrations. Growth data and antioxidant system responses were measured from the formed seedlings. In another experiment, the seeds were cultivated in vitro in the presence of graphene oxide at different concentrations. The results showed that the highest germination was observed in seeds scarified with sulfuric acid for 30 and 40 min, regardless of the addition of GA₃. After 60 days of in vitro cultivation, physical scarification and scarification time with sulfuric acid promoted greater shoot and root length. The highest seedling survival was observed when the seeds were immersed for 30 min (86.66%) and 40 min (80%) in sulfuric acid without GA₃. The concentration of 50 mg L^-1 graphene oxide favored rhizome growth, while the concentration of 100 mg L^-1 favored shoot growth. Regarding the biochemical data, the different concentrations did not influence MDA (Malondialdehyde) levels, but caused fluctuations in antioxidant enzyme activities.

The combination of graphene oxide and preservatives can further improve the preservation of cut flowers

It is reported that the use of nanomaterials can extend the vase life of fresh-cut flowers. Graphene oxide (GO) is one of these nanomaterials that aid in promoting water absorption and antioxidation during the preservation of fresh-cut flowers. In this investigation, the three mainstream brands of preservatives commercially available on the market ("Chrysal," "Floralife," and "Long Life") in combination with low concentrations of GO (0.15 mg/L) were used to preserve fresh-cut roses. The results showed that the three brands of preservatives had different degrees of freshness retention. Compared to the preservatives used alone, the combination of low concentrations of GO with the preservatives, especially in the L+GO group (with 0.15 mg/L GO added in the preservative solution of "Long life"), further improved the preservation of cut flowers. L+GO group showed less level of antioxidant enzyme activities, lower ROS accumulation and cell death rate, and higher relative fresh weight than the other groups, implying a better antioxidant and water balance abilities. GO attached to the xylem duct of flower stem, and reduced the blockage of xylem vessels by bacteria, which were determined by SEM (scanning electron microscopy) and FTIR (Fourier transform infrared) analysis. XPS (X-ray photoenergy spectra) analysis results proved that GO could enter the interior of flower stem through xylem duct, and when combined with "Long Life," the anti-oxidation protection ability of GO was enhanced, thus delaying ageing, and greatly extending the vase life of fresh-cut flowers. The study provides new insights into cut flower preservation using GO.

The combined effect of graphene oxide and elemental nano-sulfur on soil biological properties and lettuce plant biomass

The impact of graphene oxide (GO) nanocarbon on soil properties is mixed, with both negative and positive effects. Although it decreases the viability of some microbes, there are few studies on how its single amendment to soil or in combination with nanosized sulfur benefits soil microorganisms and nutrient transformation. Therefore, an eight-week pot experiment was carried out under controlled conditions (growth chamber with artificial light) in soil seeded with lettuce (Lactuca sativa) and amended with GO or nano-sulfur on their own or their several combinations. The following variants were tested: (I) Control, (II) GO, (III) Low nano-S + GO, (IV) High nano-S + GO, (V) Low nano-S, (VI) High nano-S. Results revealed no significant differences in soil pH, dry plant aboveground, and root biomass among all five amended variants and the control group. The greatest positive effect on soil respiration was observed when GO was used alone, and this effect remained significant even when it was combined with high nano-S. Low nano-S plus a GO dose negatively affected some of the soil respiration types: NAG_SIR, Tre_SIR, Ala_SIR, and Arg_SIR. Single GO application was found to enhance arylsulfatase activity, while the combination of high nano-S and GO not only enhanced arylsulfatase but also urease and phosphatase activity in the soil. The elemental nano-S probably counteracted the GO-mediated effect on organic carbon oxidation. We partially proved the hypothesis that GO-enhanced nano-S oxidation increases phosphatase activity.