Introduction

With the continuous improvement of the living standards of people throughout China, the consumption of sweet corn has also been increasing annually within the country. To meet this surging market demand, breeders are developing varieties with high sugar content. However, high sugar content in sweet corn inevitably reduces seed vitality, which leads to slow growth and development of the canopy and an inability to cope with increasingly fierce weed competition in the field1,2. Therefore, using herbicides to control weeds in the field is an inevitable management technique for sweet corn production. Nicosulfuron (NIF) is a sulfonylurea herbicide. Since 1999, nicosulfuron has been approved as a post-emergent sweet corn herbicide in some areas of the United States, but serious damage to different sweet corn varieties caused by NIF been reported frequently3,4. Therefore, determining means to enhance the tolerance of sweet corn to NIF is a critical objective in sweet corn production.

NIF, as a sulfonylurea herbicide, can reduce the synthesis of branched chain amino acids by inhibiting the activity of acetolactate synthase (ALS), affecting critical physiological processes in plants, such as photosynthesis and respiration, and ultimately leading to plant death5,6. Different-NIF tolerant sweet corn varieties exhibit different metabolic degradation rates of NIF. Compared to sensitive varieties, varieties with strong tolerance have a faster metabolic degradation rate of NIF7. Studies have shown that cytochrome P450 (CYP450) plays an important role in the metabolism of NIF8,9. Fear and Swanson studied the mechanism of resistance to monuron in cotton seedlings, and discovered that P450 in microsomes participated in the metabolism of the herbicide10. Subsequently, a large number of studies have demonstrated that P450 is involved in the metabolism of NIF in microsomes. Persans et al.11 showed that increasing the activity of CYP450 can reduce the damage of NIF to crops. Many studies have demonstrated that the sensitivity of maize to herbicides metabolized by P450 is mainly regulated by a single CYP gene or a group of closely linked CYP genes on the short arm of chromosome 5. However, at present, studies evaluating the P450 protein expression level after spraying sulfonylurea herbicides at the seedling stage and the changes of P450 protein quantity in plants before and after herbicide degradation are equivocal, which may be related to the complexity of the function of P45012,13,14,11. The results of whole genome sequencing of rice revealed 328 P450-related genes and 99 candidate P450-related genes, and the functions of most of these genes were unknown15. In addition, the low abundance of transcripts encoding P450 also makes it more difficult to study16,13,17. Therefore, further in-depth research and exploration are needed to determine how to improve the activity and quantity of CYP450 protein in crops, thereby enhancing the tolerance of corn to NIF.

Among nanomaterials, the use of graphene oxide (GO) has had one of the fastest rates of growth in recent years and has been widely used in many fields such as agriculture, biomedicine, and electronics. The application prospects of GO in agriculture are very broad. In recent years, the application of GO in slow-release fertilizer, plant pest control, and plant growth regulation has become a very active area of research18,19,20,21. Numerous studies have shown that in agricultural applications, high doses of GO exhibit toxic effects on plant growth, while low doses of GO can promote crop growth, consistent with an effect known as hormesis. Ren et al.22 reported that high concentration GO (1000 mg L–1) treatment exacerbated oxidative stress in wheat and inhibited root growth. Similarly, You et al.23 revealed that high concentrations of GO reduced rice uptake of cadmium, but also limited rice growth. In contrast, Guo et al.24 showed that low concentrations of GO (50 and 100 mg L−1) effectively increased the accumulation of dry matter in tomato plants and promoted the growth of tomato plant roots in particular. Sharma et al.25 determined that GO significantly increased the chloroplast activity of spinach leaves, thereby improving electron transfer efficiency and enhancing their photosynthetic capacity.

The application of GO as an adjuvant to increase herbicide safety has not been previously reported. To better achieve the practical application of GO herbicide nanocomposites, this study investigated the effects of GO, NIF, and GO-NIF composite materials on the photosynthesis and chlorophyll fluorescence parameters of a pair of sweet corn sister lines (to minimize the effects of genetic background differences between lines). Biochemical parameters, such as reactive oxygen species (ROS) level and antioxidant enzyme activity of sweet corn seedlings were analyzed. This study provides an empirical basis for understanding the detoxification-promoting effect of GO in NIF applications and analyzing the mechanism of GO-induced allogeneic detoxification in cells. This work also provides broader prospects for the utilization of GO in agriculture.

Results

Characterization of GO-NIF nanocomposite

Scanning electron microscopy revealed that GO exhibits layered folds and is relatively dispersed, which may provide more attachment sites for NIF (Fig. 1a and b). NIF was evenly dispersed in GO, and after mixing the two materials loading, GO still maintained its wrinkled state. The contact surface between NIF and GO showed blurred marginalization, which may be the result of mutual infiltration between NIF and GO. SME indicated successful loading of NIF into GO (Fig. 1c and d). The FT-IR spectrum data revealed peaks at 1044, 1224, 1363, 1623, and 1720 cm–1, which correspond to C-O stretching vibration, C–O–C stretching vibration, O–H bending vibration of C–OH groups, GO ring skeleton vibration, and C=O stretching vibration of carboxyl and carbonyl groups, respectively. The observed peaks at 3300–3600 cm–1 correspond to the O–H stretching vibrations of carboxyl, hydroxyl, and interlayer bound water, indicating the presence of GO in the composite material (Fig. 2). After loading, the characteristic peak of NIF was weakened, indicating that NIF participates in complex chemical reactions during the composite process. Thus, the results of FT-IR and SEM confirmed the successful synthesis of GO-NIF.

Fig. 1
figure 1

SEM images of GO(a,b) and GO-NIF (c,d).

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Fig. 2
figure 2

FT-IR spectra of GO, GO-NIF and NIF.

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Photosynthetic characteristics

The different chemical treatments had different effects on the photosynthetic characteristics of the two sweet corn varieties. As the number of days since spraying increased, the different chemical treatments did not significantly affect the A, Gs, and E values of the NIF-resistant sweet corn inbred line HK301. Compared to HK301 under control conditions (HK301-CK), the A, Gs, and E values of HK301 under GO-NIF treatment (HK301-GO-NIF) did not exhibit significant changes. In contrast, there were significant differences in the effects of the different treatments on A, Gs, and E of the NIF-sensitive sweet corn inbred line HK320. GO-NIF treatment significantly improved the A, Gs, and E values of the NIF-sensitive inbred line HK320. At 2, 4, 6, 8, and 10 days after spraying (DAS), the A value of HK320 under GO-NIF treatment (HK320-GO-NIF) significantly increased by 23.08%, 30.36%, 329.75%, 611.50%, and 328.31% compared to HK320 under NIF treatment (HK320-NIF), respectively. As the time since spraying increased, the Gs and E values of HK320-GO-NIF remained at the same level as those of HK320 under control conditions (HK320-CK), with no significant difference observed (Fig. 3). As the time since spraying increased, compared to HK301-CK, GO-NIF had no significant effect on the Ci and Ls of the tolerant sweet corn inbred line HK301, but the Ci and Ls values of the NIF-sensitive sweet corn inbred line HK320 were significantly reduced by GO-NIF treatment compared with HK320-NIF. At 2, 4, 6, 8, and 10 DAS, the Ci of HK320-GO-NIF was reduced by 23.25%, 69.86%, 110.35%, 102.67%, and 136.36%, respectively, compared with HK320-NIF. At 4, 6, 8, and 10 DAS, the Ls of HK320-GO-NIF was significantly reduced by 52.44%, 64.89%, 46.73%, and 33.61%, compared to HK320-NIF, respectively (Fig. 4).

Fig. 3
figure 3

Effects of different chemical treatments on the net photosynthetic rate (A) (A,B), stomatal conductance (Gs) (C,D) and transpiration rate (E) (E,F) in leaves of sweet maize seedlings. HK301-CK: clean water treatment in HK301; HK301-NIF: nicosulfuron 80 mg·kg–1 treatment in HK301; HK301-GO: GO 80 mg·kg–1 treatment in HK301; HK301-GO-NIF: GO-NIF 80 mg·kg–1 treatment in HK301; HK320-CK: clean water treatment in HK320; HK320-NIF: nicosulfuron 80 mg·kg–1 treatment in HK320; HK320-GO: GO 80 mg·kg–1 treatment in HK320; HK320-GO-NIF: GO-NIF 80 mg·kg–1 treatment in HK320; Vertical bars represent the SE (n = 6). The lowercase letters (a, b) represent the difference (P < 0.05) between the values obtained on the same day after different chemical treatments using the Least Significant Difference (LSD) test.

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Fig. 4
figure 4

Effects of different chemical treatments on the intercellular CO2 concentrations (Ci) (A,B) and limited stomatal value (Ls) (C,D) in leaves of sweet maize seedlings. HK301-CK: clean water treatment in HK301; HK301-NIF: nicosulfuron 80 mg·kg–1 treatment in HK301; HK301-GO: GO 80 mg·kg–1 treatment in HK301; HK301-GO-NIF: GO-NIF 80 mg·kg–1 treatment in HK301; HK320-CK: clean water treatment in HK320; HK320-NIF: nicosulfuron 80 mg·kg–1 treatment in HK320; HK320-GO: GO 80 mg·kg–1 treatment in HK320; HK320-GO-NIF: GO-NIF 80 mg·kg–1 treatment in HK320; Vertical bars represent the SE (n = 6). The lowercase letters (a, b) represent the difference (P < 0.05) between the values obtained on the same day after different chemical treatments using the Least Significant Difference (LSD) test.

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Chlorophyll fluorescence parameters

After spraying different chemical treatments, there was no significant difference in photosystem II (PSII) photochemical maximum quantum yield (Fv/Fm) between the treatments of the NIF-resistant inbred line HK301 as the days since spraying increased. Compared with the resistant inbred line HK301, the Fv/Fm value of the sensitive inbred line HK320 showed a continuous downward trend after spraying NIF, reaching its minimum value at 10 DAS. After spraying, GO-NIF significantly increased the Fv/Fm of HK320 compared to the NIF treatment. At 10 DAS, the Fv/Fm of HK320-GO-NIF increased by 73.53% compared to HK320-NIF. At 2 and 6 DAS, GO- NIF significantly increased the photochemical quenching coefficient (qp) value of HK320, and compared to HK301 under NIF treatment, the qp of under GO-NIF treatment increased by 9.62% and 13.81%, respectively. As the days since spraying increased, the qp value of HK320 showed a continuous downward trend. In contrast, after spraying GO-NIF, the qp of HK320 was maintained at a high level, with no significant difference compared to control conditions (Fig. 5).

Fig. 5
figure 5

Effects of different chemical treatments on the PSII photochemistry (Fv/Fm). (A,B) and photochemical quenching coefficient (qP) (C,D) in leaves of sweet maize seedlings. HK301-CK: clean water treatment in HK301; HK301-NIF: nicosulfuron 80 mg·kg–1 treatment in HK301; HK301-GO: GO 80 mg·kg–1 treatment in HK301; HK301-GO-NIF: GO-NIF 80 mg·kg–1 treatment in HK301; HK320-CK: clean water treatment in HK320; HK320-NIF: nicosulfuron 80 mg·kg–1 treatment in HK320; HK320-GO: GO 80 mg·kg–1 treatment in HK320; HK320-GO-NIF: GO-NIF 80 mg·kg–1 treatment in HK320; Vertical bars represent the SE (n = 6). The lowercase letters (a, b) represent the difference (P < 0.05) between the values obtained on the same day after different chemical treatments using the Least Significant Difference (LSD) test.

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The electron transfer rate (ETR) of HK301 was lower than the control level at 4 DAS. As the time since spraying increased, it returned to the control level at 10 DAS, and there was no significant difference compared to other chemical treatments. At 2 DAS, the ETR of HK320 began to show a downward trend and reached its minimum value at 8 DAS. In contrast, after GO-NIF treatment, the ETR of HK320 remained at a high level, with no significant difference compared to the control. At 10 DAS, the ETR of HK320-GO-NIF significantly increased by 127.04% compared to HK320 under NIF treatment. After spraying NIF, the nonphotochemical quenching (NPQ) of HK301 was only higher than that of the control at 4 and 6 DAS and then returned to the control level. However, after spraying GO-NIF, there was no significant difference in NPQ between HK301 and the control. After spraying NIF, the NPQ of HK320 showed a continuous upward trend, reaching its maximum at 10 DAS. In contrast, GO-NIF was able to maintain the NPQ value of HK320 at a lower level, which was not significantly different from that of the control. At 2, 4, 6, 8, and 10 DAS, the NPQ value of HK320-GO-NIF was reduced by 22.38%, 32.85%, 78.01%, 104.91%, and 76.06% compared to HK320 under NIF treatment alone (Fig. 6).

Fig. 6
figure 6

Effects of different chemical treatments on the electron transport rate (ETR) (A,B) and photochemical quenching (NPQ) (C,D) in leaves of sweet maize seedlings. HK301-CK: clean water treatment in HK301; HK301-NIF: nicosulfuron 80 mg·kg–1 treatment in HK301; HK301-GO: GO 80 mg·kg–1 treatment in HK301; HK301-GO-NIF: GO-NIF 80 mg·kg–1 treatment in HK301; HK320-CK: clean water treatment in HK320; HK320-NIF: nicosulfuron 80 mg·kg–1 treatment in HK320; HK320-GO: GO 80 mg·kg–1 treatment in HK320; HK320-GO-NIF: GO-NIF 80 mg·kg–1 treatment in HK320; Vertical bars represent the SE (n = 6). The lowercase letters (a, b) represent the difference (P < 0.05) between the values obtained on the same day after different chemical treatments using the Least Significant Difference (LSD) test.

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ROS content

O2 − production rate

After spraying NIF, the O2− production rate of HK301 first increased and then decreased, significantly increasing by 50.38% and 22.98% compared to the control at 2 and 4 DAS, respectively. After spraying GO-NIF, the O2− production rate of HK301 was only higher than the control at 2 DAS. As the spraying time increased, the O2− production rate of HK301 remained at the control level. After spraying NIF, the O2− production rate of the NIF-sensitive inbred line HK320 showed an upward trend, reaching its maximum value at 10 DAS and reaching a significant difference compared to the other treatments. After spraying GO-NIF, there was no significant difference in the O2− production rate of HK320 compared to the control (Fig. 7A and B).

Fig. 7
figure 7

Effects of different chemical treatments on the O2- production rate (A,B), and H2O2 (C,D) in leaves of sweet maize seedlings. HK301-CK: clean water treatment in HK301; HK301-NIF: nicosulfuron 80 mg·kg–1 treatment in HK301; HK301-GO: GO 80 mg·kg–1 treatment in HK301; HK301-GO-NIF: GO-NIF 80 mg·kg–1 treatment in HK301; HK320-CK: clean water treatment in HK320; HK320-NIF: nicosulfuron 80 mg·kg–1 treatment in HK320; HK320-GO: GO 80 mg·kg–1 treatment in HK320; HK320-GO-NIF: GO-NIF 80 mg·kg–1 treatment in HK320; Vertical bars represent the SE (n = 6). The lowercase letters (a, b) represent the difference (P < 0.05) between the values obtained on the same day after different chemical treatments using the Least Significant Difference (LSD) test.

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H2O2 content

After spraying NIF, the H2O2 content of the NIF-sensitive inbred line HK320 showed a continuous upward trend, reaching its maximum at 10 DAS, which was significantly, by 652.15%, 665.52%, and 707.75%, higher than that of the control, GO, and GO-NIF treatments, respectively. After spraying NIF, the H2O2 content of HK301 was significantly higher than that of the control only at 2 and 4 DAS. As time since spraying increased, the H2O2 content of HK301 returned to the control level (Fig. 7C and D).

Antioxidant enzyme activities

SOD activity

As time since spraying NIF increased, the SOD enzyme activity of the NIF-resistant inbred line HK301 showed a trend of first increasing and then decreasing, but remained significantly higher than that of the control. After spraying GO-NIF, the SOD enzyme activity of HK320 was significantly higher than that of the control, except at 8 DAS. After spraying NIF, as time since spraying increased, the SOD activity of HK320 showed a trend of first increasing and then decreasing. At 6, 8, and 10 DAS, the SOD activity of HK320 was significantly reduced by 26.38%, 75.50%, and 99.69% compared to the control. After spraying GO-NIF, the SOD activity of HK320 reached its maximum at 8 DAS, followed by a downward trend, but was still significantly higher than that of the control throughout the course of the experiment. Compared to HK320-NIF, the SOD activity of HK320-GO-NIF increased by 24.69%, 50.18%, 187.55%, and 209.83% at 4, 6, 8, and 10 DAS, respectively (Fig. 8A and B).

Fig. 8
figure 8

Effects of different chemical treatments on the SOD (A,B) and POD (C,D) in leaves of sweet maize seedlings. HK301-CK: clean water treatment in HK301; HK301-NIF: nicosulfuron 80 mg·kg–1 treatment in HK301; HK301-GO: GO 80 mg·kg–1 treatment in HK301; HK301-GO-NIF: GO-NIF 80 mg·kg–1 treatment in HK301; HK320-CK: clean water treatment in HK320; HK320-NIF: nicosulfuron 80 mg·kg–1 treatment in HK320; HK320-GO: GO 80 mg·kg–1 treatment in HK320; HK320-GO-NIF: GO-NIF 80 mg·kg–1 treatment in HK320; Vertical bars represent the SE (n = 6). The lowercase letters (a, b) represent the difference (P < 0.05) between the values obtained on the same day after different chemical treatments using the Least Significant Difference (LSD) test.

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POD activity

Compared to the control, both NIF and GO-NIF treatments significantly increased the POD activity of HK301. Except at 8 DAS, the POD activity under NIF treatment was significantly higher than that under GO-NIF treatment on all other evaluated days. The POD activity of HK301-NIF was 20.31%, 51.46%, 34.52%, 8.15%, and 43.82% higher than that of HK301-GO-NIF, respectively. After spraying NIF, the POD activity of HK320 showed a trend of first increasing and then decreasing and was significantly lower than that of the control at 6, 8, and 10 DAS. After spraying GO-NIF, the POD activity of HK320 showed a continuous upward trend, reaching its maximum at 10 DAS. Compared to HK320-NIF, the POD activity of HK320-GO-NIF increased by 60.08%, 60.93%, 450.00%, 421.43%, and 765.28% at 2, 4, 6, 8, and 10 DAS, respectively (Fig. 8C and D).

CAT activity

At 4 DAS NIF, the CAT activity of the NIF-resistant inbred line HK301 showed a continuous upward trend and was significantly higher than that of the other treatments. After 2 DAS with GO-NIF, the CAT activity of HK301 showed a continuous upward trend. Compared to HK301-CK, the CAT activity of HK301-GO-NIF increased by 36.29%, 50.74%, 89.69%, and 62.73% at 4, 6, 8, and 10 DAS, respectively. At 2 DAS NIF, the CAT activity of the NIF-sensitive inbred line HK320 reached its maximum value, followed by a decrease, and reached its minimum value at 10 DAS. In comparison, after spraying GO-NIF, the CAT activity of HK320 showed an upward trend, reaching its maximum at 6 DAS and remained at a relatively high level over time. At 4, 6, 8, and 10 DAS, the CAT activity of HK320-GO-NIF increased by 19.15%, 215.90%, 309.71%, and 550.53%, respectively, compared to HK320-NIF (Fig. 9A and B).

Fig. 9
figure 9

Effects of different chemical treatments on the CAT (A,B) and APX (C,D) in leaves of sweet maize seedlings. HK301-CK: clean water treatment in HK301; HK301-NIF: nicosulfuron 80 mg·kg–1 treatment in HK301; HK301-GO: GO 80 mg·kg–1 treatment in HK301; HK301-GO-NIF: GO-NIF 80 mg·kg–1 treatment in HK301; HK320-CK: clean water treatment in HK320; HK320-NIF: nicosulfuron 80 mg·kg–1 treatment in HK320; HK320-GO: GO 80 mg·kg–1 treatment in HK320; HK320-GO-NIF: GO-NIF 80 mg·kg–1 treatment in HK320; Vertical bars represent the SE (n = 6). The lowercase letters (a, b) represent the difference (P < 0.05) between the values obtained on the same day after different chemical treatments using the Least Significant Difference (LSD) test.

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APX activity

After spraying NIF, as time since spraying increased, the APX activity of HK301 showed a trend of first increasing and then decreasing, but was significantly higher than that of the control at each time point assayed. After spraying GO-NIF, the APX activity of HK301 showed a continuous increasing trend, and at 6, 8, and 10 DAS with NIF, the APX activity of HK301 was significantly higher than that of the control. At 6 DAS NIF, the APX activity of HK320 showed a decreasing trend and was significantly lower than that of the control. At 6 DAS GO-NIF, the APX activity level of HK320 reached its maximum value and subsequently remained at a high level of APX activity. Compared to HK320-NIF, the APX activity level of HK320-GO-NIF increased by 159.43%, 453.43%, 590.51%, and 693.43% respectively at 4, 6, 8, and 10 DAS (Fig. 9C and D).

Discussion

NIF has been widely used as a post-emergent herbicide for weed control in maize fields. Although NIF has been applied for nearly 30 years, some waxy and especially sweet corn varieties are still frequently reported to be damaged by NIF26,27,4. Improving the safety of NIF application in sweet corn cultivation is a key focus of researchers. In the present study, the combination of graphene oxide (GO) as a protective adjuvant and NIF was able to effectively improve the resistance of sweet corn, which indicates the promising possibility for the safe use of NIF in sweet corn cultivation. Many herbicides, including NIF, act as photosynthetic inhibitors by interfering with electron transfer, causing obvious yellowing and ultimately necrosis of plant leaves28,29,30. A similar effect occurs when plant leaves are treated with atrazine. When atrazine binds to the D1 protein of PSII, electron transfer is blocked31,28. Although NIF is intended to target specific regions of plants, there is evidence that NIF also significantly reduces the plant’s photosynthetic rate, contents of photosynthetic pigments, and photosynthetic associated protein activity31,2. In our study, as the days since spraying increased, compared with the NIF-resistant inbred line HK301, NIF treatment significantly reduced A, Gs, and E values of the NIF-sensitive inbred line HK320, while Ci and Ls both significantly increased. In contrast, GO-NIF treatment was able to significantly increase the A, Gs, and E values of HK320 and keep the Ci and Ls values of HK320 at a relatively low level. This indicates that GO, as a protective adjuvant against the damage caused by NIF, can effectively reduce non-stomatal limiting factors, enabling the NIF-sensitive HK320 to maintain its strong photosynthetic capacity.

Various herbicide types (such as atrazine and diazuron) have action sites in PS II within the photoreaction center36. Chlorophyll fluorescence is an effective means of evaluating the PSII system in photo-reactions, which can clearly demonstrate the efficacy of such herbicides32. In our study, compared to HK301, NIF treatment significantly reduced the Fv/Fm, qP, and ETR of HK320, while NPQ significantly increased. In contrast, GO-NIF treatment significantly improved the Fv/Fm, qP, and ETR values of HK320, while NPQ did not significantly increase. These findings indicated that GO can effectively alleviate the damage caused by herbicides to plants, allowing the light energy absorbed by chloroplasts to dissipate quickly in the PSII system without being converted into heat. This further demonstrates that the mechanism of interaction between light and herbicides is indirect, and in PS II, i.e., light does not directly act on the herbicide target. Herbicides that inhibit electron flow in PS II have been shown to competitively bind to D1 proteins. This competition causes the PSII-QB site to be replaced from its binding site by herbicide, which prevents electrons from flowing through PSII33,34. Our study further demonstrated that after spraying NIF, the ETR of the NIF-sensitive inbred line HK320 significantly decreased compared to that of the NIF-resistant inbred line HK301, while GO-NIF treatment was able to significantly increase the ETR of HK320. Zhou et al.35 shows that in the presence of GO, the plant displayed a better ability to regulate the photosynthetic electron transfer at PSII receptor side, and their light energy conversion efficiency and photosynthetic performance were enhanced. Our study indicates that GO can effectively reduce the competitive binding between herbicides and D1 protein, and its mechanism of action will be the focus of our future research.

Under natural and stress conditions, the photosystem I, PSII, and mitochondrial mediated electron transport in maize are the main sites of ROS production. Accordingly, the presence of the abiotic stress factor NIF uses the same electron transport system to increase ROS production and thus accelerate physiological and biochemical damage in maize36,6. Our study shows that compared to NIF treatment, GO-NIF treatment significantly reduced the O2− production rate and H2O2 content of HK320. It has been shown that the content of O2− and H2O2 in maize seedlings significantly increased after spraying NIF and isoproturon30,37. Our experimental results demonstrate that GO can effectively slow ROS production, thereby reducing the damage to sweet corn seedlings caused by NIF. The antioxidant system plays an important role in clearing ROS in plants and preventing plant cell damage caused by herbicide stress. In the antioxidant system, SOD completes the catalytic reaction of O2− to H2O237. Subsequently, H2O2 decomposes into H2O through the main H2O2 scavenging enzymes CAT and POD as well as APX in the ascorbate–glutathione cycle pathway38,39. In our study, GO-NIF treatment maintained the stability of ROS in plants by increasing the SOD, POD, CAT, and APX activities of HK320, thereby enabling the balance of redox reactions in plants. These findings suggest that the clearance rate of ROS by antioxidant enzymes under GO treatment is greater than the accumulation rate of ROS itself, thus reducing the damage caused by ROS to the PSII reaction center in chloroplasts, ensuring the integrity of the chloroplast structure, and greatly improving the photochemical catalytic efficiency of the NIF-sensitive variety.

Conclusion

Our research revealed that spraying low concentrations of GO alone had no effect on the growth of a pair of sweet corn inbred seedlings. However, compared to NIF treatment alone, the application of GO, as a protective adjuvant for the use of NIF, was able to significantly enhance the resistance of the NIF-sensitive sweet corn inbred line HK320 to NIF. Compared to NIF treatment alone, GO-NIF treatment was able to effectively maintain the A, E, Gs, Fv/Fm, qP, and ETR values of the NIG-sensitive inbred line HK320, while also maintaining its strong photosynthetic capacity and its high PSII activity. Compared with NIF treatment alone, GO-NIF treatment significantly reduced the ROS level of HK320, which was owing to the fact that GO-NIF mobilized the antioxidant system, improved the activity of antioxidant enzymes to clear ROS in HK320, and maintained the redox reaction balance in sweet corn seedlings. This study provides a valuable empirical basis for understanding both the detoxification promoting effect of GO in herbicides and the mechanism of GO-induced cell heterologous detoxification, while also providing broader prospects for the application of nano pesticides and new strategies for weed control in sweet corn cultivation.

Material and methods

Plant material

The experimental plant materials were a pair of sweet corn sister lines developed by the special corn breeding team of Hebei Normal University of Science and Technology (HNUST) Qinhuangdao, Hebei, China; these lines differed in their tolerance to NIF. Wu et al.2 and Xu et al.40 conducted herbicide concentration screening experiments in the early stage, when the NIF spraying concentration was 80 mg kg–1, HK301 could grow normally, while HK320 ultimately withered and died. This indicates that sweet corn inbred line HK301 showed tolerance to NIF, while sweet corn inbred line HK320 was sensitive to NIF.

Experimental design and herbicide treatment

In 2022–2023, a field test was conducted at Changli Experimental Station (40°4′N, 118°95′E) of HNUST. The area is located in the east of Hebei Province, China, which has a warm temperate and semi humid continental climate. The soil type of the test site is medium loam. The soil organic matter content was 18.47 g kg–1, the total nitrogen content was 1.51 g kg–1, alkaline hydrolyzed nitrogen content was 109.32 mg kg–1, available phosphorous was 17.32 mg kg–1, and available potassium was 74.35 mg kg–1. The experiment adopted a randomized block design with three replicates. The length of each test plot was 5 m, with 10 rows and a plot area of 30 m2. In order to ensure an appropriate number of seedlings, three seeds were planted at each point.

In 2021–2022, GO, NIF, and GO-NIF concentration screening tests were conducted at HNUST, Qinhuangdao (39°25′N, 118°45′E), Hebei Province, China; at Zhejiang Academy of Agricultural Sciences in Dongyang (28°63′N, 120°31′E), Zhejiang Province; and at Zhejiang Province South Breeding Experimental Base in Sanya (18°34′N, 108°42′E), Hainan Province. NIF solutions of different concentrations (0, 20, 40, 80, and 120 mg kg–1) were prepared by diluting the stock solution. The GO powder was dissolved using deionized water and then ultrasonically treated for 40 min to prepare a stock solution. GO solutions of different concentrations (0, 20, 40, 80 and 120 mg kg–1) were prepared by diluting the stock solution. The five different concentrations of GO solutions in a 1:1 ratio (V:V) were added to different concentrations of NIF solutions to form treatment solutions, as follows: 0 mg kg–1 = 0 GO + 0 NIF, 20 mg kg–1 = 20 GO + 20 NIF, 40 mg kg–1 = 40 GO + 40 NIF, 80 mg kg–1 = 80 GO + 80 NIF, 120 mg kg–1 = 120 GO + 120 NIF. An electric backpack sprayer was used to treat corn seedlings with the water (control), GO, NIF and GO-NIF treatments. The survival rate during the four-leaf one-heart stage of seedlings was evaluated. This screening revealed that when the NIF concentration was 80 mg kg−1, HK320 seedlings sprayed with GO-NIF were able to survive normally, reducing the toxic effects of NIF on HK320 (Table 1). In 2022–2023, an experiment was conducted in the field. During the four-leaf one-heart stage of corn seedlings, GO, NIF, GO-NIF, and clean water were sprayed at 80 mg kg–1 using a laboratory pot sprayer equipped with a nozzle, respectively. After spraying, samples were collected every two days and stored in a − 80 °C freezer prior to the determination of physiological indicators.

Table 1 Effect of different chemical treatments on the survival rate of sweet corn seedlings.
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GO preparation and characterization

Commercially available graphite powders were oxidized and stripped to GO according to a modified version of the method of Hummers and Offeman41. The morphology of GO and GO-NIF nanocomposites was observed by scanning electron microscopy (SU8010; Hitachi, Tokyo, Japan). FT-IR spectroscopy (TENSOR-27; Bruker, Billerica, MA, USA) was used to detect the infrared absorption spectra of GO and GO-NIF nanocomposites at 25 °C.

Gas exchange properties

The photosynthetic indicators were measured using a Li-6800 instrument (Li COR, Lincoln, NE, USA) from 9:00 to 11:00. During the test, 6800-02 LED red and blue light sources were used, and the effective photosynthetic radiation inside the leaf chamber was set to 1000 μmol CO2 m–2 s–1; atmospheric CO2 was obtained by connecting a custom-made buffer bottle, and the temperature was set to 20℃. Six plants were selected for each treatment, and the fourth fully unfolded leaf of sweet corn seedlings was measured.

Chlorophyll fluorescence parameters

The chlorophyll fluorescence parameters were determined with the PAM-2500 portable modulated chlorophyll fluorometer PAM2500 (Heinz Walz GmbH, Effeltrich, Germany). The fourth fully unfolded leaf was selected for each treatment for determination. Before determination, each tested leaf was clamped and dark adapted for 30 min. Then, the initial fluorescence (Fo) was first determined. The maximum fluorescence (Fm) was then determined by irradiation of saturated pulsed light (10,000 μmol m–2 s–1) for 0.5 s. The leaves were irradiated with 500 μmol m–2 s–1 activated light. When Ft stabilized, the saturated pulse light was turned on again to measure Fm’; the activation light was turned off, while the far-red light was turned on for 5 s, and Fo’ was then determined. The maximum quantum yield of PSII photochemistry (Fv/Fm), electron transport rate (ETR), photochemical quenching coefficient (qP), and nonphotochemical quenching (NPQ) were each calculated according to the method of Wu et al.2.

O2 − production rate and H2O2 content

According to the method of Wang et al.42 the O2− production rate and H2O2 content of maize leaves were detected.

Antioxidant enzyme activities

Superoxide dismutase (SOD, EC 1.15.1.1), guaiacol peroxidase (POD, EC 1.11.1.7), catalase (CAT, EC 1.11.1.6), and ascorbate peroxidase (APX, EC 1.11.1.11) kits obtained from Suzhou Keming Biotechnology Co., Ltd. were used for enzyme activity determination as directed by the manufacturer’s instructions.

Statistical analyses

Microsoft Excel (Microsoft Corp., Redmond, WA, USA) and SigmaPlot 12.5 (Systat Software, Inc., San Jose, CA, USA) were used for data analysis and plotting. Each data point reported is the mean ± standard error (SE) of three biological replicates versus three experimental replicates. Analysis of variance (ANOVA) was performed using SPSS version 12.0 (SPSS Inc., Chicago, IL, USA).

Experimental research and field studies on plants statement

In the study only cultivated plants were used which are neither endangered nor at risk of extinction. We confirm that their handling was performed in compliance with relevant institution, national and international guidelines and legislation.

Statement on guidelines

All experimental studies and experimental materials involved in this research are in full compliance with relevant institutional, national, and international guidelines and legislation.