Effect of exogenous glucose and fulvic acid on accumulate cadmium Cd of Mirabilis jalapa L. Vertical bars represent standard deviation of the means (n = 3). The uppercase letters show the statistical difference in determined indexes among different treatments of fulvic acid, and the lowercase letters indicate the difference in determined indexes among different treatments of glucose. The same letter indicates no significant difference at α = 0.05 level.
Effect of exogenous glucose and fulvic acid on antioxidative enzyme activities and MDA content of Mirabilis jalapa L. Vertical bars represent standard deviation of the means (n = 3). The uppercase letters show the statistical difference in determined indexes among different treatments of fulvic acid, and the lowercase letters indicate the difference in determined indexes among different treatments of glucose. The same letter indicates no significant difference at α = 0.05 level.
Effect of exogenous glucose and fulvic acid on photosynthetic parameters of Mirabilis jalapa L. Vertical bars represent standard deviation of the means (n = 3). The uppercase letters show the statistical difference in determined indexes among different treatments of fulvic acid, and the lowercase letters indicate the difference in determined indexes among different treatments of glucose. The same letter indicates no significant difference at α = 0.05 level.
Effect of exogenous glucose and fulvic acid on chlorophyll fluorescence parameters of Mirabilis jalapa L. Vertical bars represent standard deviation of the means (n = 3). The uppercase letters show the statistical difference in determined indexes among different treatments off acid, and the lowercase letters indicate the difference in determined indexes among different treatments of glucose. The same letter indicates no significant difference at α = 0.05 level.
Correlation analysis of transpiration regulator on photosynthesis and antioxidant enzymes of Mirabilis jalapa L.
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Using ornamental plants for phytoremediation can not only remove pollutants from the environment but also beautify and purify it. The purpose of this study was to investigate the effects of exogenous spraying of transpiration regulators glucose (Glc) and fulvic acid (FA) on the growth, biomass, and cadmium (Cd) enrichment of Mirabilis jalapa L. It was found that Glc could promote the growth and biomass accumulation of M. jalapa L., whereas FA had no significant effect, with a particularly notable 77.3% increase in leaf biomass observed in the exogenous spraying of 4% Glc treatment compared with control. Glc promoted the translocation of Cd from roots to shoots by enhancing transpiration, whereas FA led to more Cd accumulation in roots. In the exogenous spraying of 4% Glc treatment, Cd enrichment in leaves increased by 138.6% compared with the control group. The bioconcentration factor and translocation factor of 4% Glc treatment were 2.4 and 2.2 times that of the control treatment, respectively. The removal rate was 2.35 times that of the control treatment. Further, both Glc and FA enhanced the antioxidant enzyme system of M. jalapa L. Exogenous spraying of Glc significantly increased the superoxide dismutase activity. Peroxidase activity increased by 58% of 4% Glc treatment compared with the control. In addition, exogenous spraying of Glc increased the net photosynthetic rate, 4% Glc treatment was 3.1 times higher than the control treatment, and the yield was 1.1 times greater in T1 treatment compared with control treatment. There was no significant effect on Pn at low concentration FA but a significant increase at high concentrations. In summary, exogenous spraying of 4% Glc can be used as an effective strategy to promote enrichment of Cd by M. jalapa L. and alleviate the oxidative stress caused by Cd, which provides a new method for phytoremediation of Cd-contaminated soil.
Heavy metal contamination in soil is a growing environmental issue caused by rapid global industrialization and mining operations (Sahito et al. 2023). Phytoremediation, the use of plants to remove environmental contaminants, is considered a cost-effective alternative to traditional remediation methods (Yu et al. 2023). Mirabilis jalapa L., as an ornamental plant, is known for its strong environmental adaptability and reproductive capacity and has also attracted much attention due to its potential application in the field of phytoremediation (Li et al. 2022; Liu et al. 2018; Zhou et al. 2012). The efficiency of phytoremediation is influenced by plant growth status and accumulation capacity, which can be improved by increasing the biomass of harvestable parts and metal accumulation (Chen et al. 2024). Strategies such as shortening the plant extraction cycle can also enhance the efficiency of plant extraction (Ashraf et al. 2019) or by collecting dead leaves to remove plant-extracted heavy metals (Wang et al. 2019). Although most plants accumulate cadmium (Cd) primarily in their roots, hyperaccumulators can store significant amounts in aboveground tissues (Wen et al. 2024; Yang et al. 2021). Previous studies have shown that high transpiration rates and well-developed root systems can promote the accumulation of Cd in the aboveground parts of rapeseed (Gao et al. 2010). Similarly, transpiration rates also play a great role in the absorption and transport of Cd in Phytolacca americana L. and Nicotiana tabacum L. (Liu et al. 2010, 2016).
Transpiration regulators can reduce leaf transpiration by forming a film on the leaf surface, increasing the diffusion resistance of stomata to water vapor and applications in agriculture (Zhang and Zhang 2014). Fulvic acid (FA), as a plant antitranspirant, is sprayed on the surface of plant leaves, which can increase stomatal transpiration resistance and reduce stomatal transpiration (AbdAllah et al. 2018). Glucose (Glc) can enhance the transpiration rate of plants, and studies have shown that spraying with 4% Glc can increase the transpiration rate of Brassica juncea L. by more than 29% (Sami and Hayat 2019). Given the key role of transpiration in the absorption and transport of Cd by plants, understanding the effects of transpiration regulators on Cd absorption by M. jalapa L. is crucial.
The objective of this study was to explore the effects of transpiration regulators, specifically the transpiration promoter Glc and the antitranspirant FA, on the photosynthetic efficiency and heavy metal enrichment capacity of M. jalapa L. We aimed to improve the phytoremediation efficiency of M. jalapa L. for Cd-contaminated soils, providing a scientific foundation for the development of effective remediation strategies.
The seeds of M. jalapa L. were provided by the Ecology Laboratory of Kunming University of Science and Technology in the present study. The soil was prepared from campus soil spiked by CdCl2·2.5 H2O, and the Cd concentration was 25 mg·kg−1. The soil was thoroughly mixed and equilibrated for 2 months to ensure homogeneity and stability of the contaminant within the matrix.
The seeds of M. jalapa L. were sterilized with 1% KMnO4 solution and then seeded in a flowerpot filled with contaminated soil. Five seeds were sowed in each pot. When the seedlings grew to 7 to 10 cm high, three seedlings were left in each pot. After 1 month of plant growth, transpiration promoter (Glc) (Sami and Hayat 2019) and antitranspiration (FA) (AbdAllah et al. 2018) were sprayed. Glc and FA were applied as follows: T0: 0, T1: 2%, T2: 4%, T3: 8% and T0: 0, T1: 0.1%, T2: 0.2%, T3: 0.4%, respectively; deionized water was sprayed as control. Each spraying time should be carried out after 4:00 PM, and the spray should be evenly applied to the leaf surface without causing dripping. After 5 d of continuous spraying, the photosynthetic parameters and chlorophyll fluorescence parameters were measured in sunny weather to harvest the plants.
The photosynthetic parameters were measured before sample harvest. Third fully expanded leaves (top to bottom) were used for measurements using the Li-6400 portable photosynthesis system (LI-6400XT; Lincoln, NE, USA). The measurements included net photosynthetic rate (Pn, µmol CO2 m−2·s−1), stomatal conductance (Gs, µmol H2O m−2·s−1), transpiration rate (E, mmol H2O m−2·s−1), and intercellular CO2 concentration (Ci, µmol CO2 mol−1) were determined according to Gao et al. (2019). The external CO2 concentration was ∼400 ± 10 µmol·mol−1. The light series of photosynthetic light flux density were set as follows: 0 µmol·m−2·s−1, 15 µmol·m−2·s−1, 30 µmol·m−2·s−1, 60 µmol·m−2·s−1, and 120 µmol·m−2·s−1, 250 µmol·m−2·s−1, 500 µmol·m−2·s−1, 1000 µmol·m−2·s−1, 1500 µmol·m−2·s−1, and 2000 µmol·m−2·s−1. All the measurements were carried out from 0900 to 1100 HR and 1400 to 1600 HR on clear-sky, sunny days.
The fully developed functional leaves (the third layer leaves at the shoot top) were collected from each treatment, and the chlorophyll fluorescence was measured with a Mini-PAM (WALZ, Effeltrich, Germany). The middle of each leaf was clamped using leaf clip (DLC-8) for the dark adaptation 30 min for chlorophyll fluorescence induction kinetics curves measurement. The induction curve was performed by setting the actinic light intensity to 611 µmol·m−2·s−1. Rapid light curves was set the PAR gradient to 0 µmol·m−2·s−1, 30 µmol·m−2·s−1, 111 µmol·m−2·s−1, 232 µmol·m−2·s−1, 397 µmol·m−2·s−1, 611 µmol·m−2·s−1, 859 µmol·m−2·s−1, 1297 µmol·m−2·s−1, 1810 µmol·m−2·s−1, with 20 s of duration. Chlorophyll fluorescence induction kinetics and rapid light curves of M. jalapa L. with different propagations were measured from 0900 to 1100 HR under clear-sky, sunny conditions (Gao et al. 2019). The fluorescence parameter was connected to a computer with the data acquisition WinControl-3.22 software. The actual quantum yield (Yield), electron transfer rate (ETR), maximal fluorescence (Fm), the maximal PSII photochemical efficiency (Fv/Fm), photochemical quenching (qP), and nonphotochemical quenching (qN) were measured and record.
Leaves were chosen after determining the photosynthesis and chlorophyll fluorescence parameters. Two 0.68-cm2 pieces of leaves were cut using a punch, cut into filaments, and then extracted in 5 mL of 80% acetone in a brown bottle overnight at room temperature in the dark (sealed). Chl a, Chl b, and carotenoids (Car) were measured by spectrophotometric (ultraviolet/VIS 750), and then the visible absorbance was recorded at 663, 646, and 470 nm, respectively. Calculations were performed following the method described by Arnon (1949). Chlorophyll content was expressed per unit leaf area (µg Chl/cm2).
The plants were harvested after 50 d of growth. The plants were carefully washed with tap water, 0.1 mol·L−1 dilute HCl, and deionized water. The plant materials were divided into two parts: one part was dried to constant weight for the determination of Cd, and the other part was stored at −18 °C. The activities of antioxidant enzymes and malondialdehyde (MDA) content were measure. Superoxide dismutase (SOD) activities in plant leaves were determined by the nitro blue tetrazolium method, catalase (CAT) activity was determined by ultraviolet spectrophotometry, peroxidase (POD) activity was determined by guaiacol method, and MDA content was determined by thiobarbituric acid method (Wang et al. 2021).
The total Cd concentrations of plant samples and soil samples were digested with HNO3-H2O2 and aqua regia-HClO4, respectively (An et al. 2019). The total concentrations of Cd in the digests were determined by flame atomic absorption spectrometry (FAAS, Model AA240FS; Varian, Palo Alto, CA, USA).
The certified reference materials for the chemical composition of soil (GBW07447) and biological sample (GBW10048) for plants obtained from Institute of Geophysical and Geochemical Exploration Co., Ltd, Langfang, Hebei, China. The results were considered satisfactory when within a range of ±10% of the certified values. The results were accepted when the relative standard deviation was within 5%.
The bioconcentration factor (BCF) was Cd concentration in leaves divided by Cd concentration in soil. Translocation factor (TF) was Cd concentration in leaves divided by Cd concentration in roots. The data were processed in Microsoft Excel 2013 and figures drawn by Origin 9.0. The results are presented as mean ± standard deviation (n = 3). Data were analyzed for one- or two-way analysis of variance (ANOVA) by using statistical product and service solutions (SPSS 20.0 Inc., Chicago, IL, USA). Significantly different means were subjected to multiple comparison by Tukey honestly significant difference test at the α = 0.05 level.
The effect of exogenous spraying transpiration regulators on the growth of M. jalapa L. is shown in Table 1. Transpiration regulators increased the plant height of M. jalapa L.; however, varying concentrations showed no significant differences in their effects (P > 0.05). Similarly, the root length of M. jalapa L. increased upon application of transpiration regulators, yet the high concentration of Glc (T3) exhibited a notable inhibitory effect on root elongation, while concurrently promoting an increase in stem and leaf biomass.
The influence of exogenous FA application on M. jalapa L. growth is also examined. No significant effects were observed for different treatment of FA on plant height, root length, and stem and leaf biomass of M. jalapa L. (P > 0.05). After the application of Glc, there was a general enhancement in the biomass of M. jalapa L., with a particularly notable 77.3% increase in leaf biomass and 21.7% increase in root biomass observed in the T2 treatment compared with the control. This suggests that Glc may have a promotional effect on the growth and biomass accumulation of M. jalapa L. As a transpiration inhibitor, FA increased root biomass by 76.7% and leaf biomass by 39.4% in T2 treatment compared with the control group. However, the root biomass of high concentration T3 treatment was lower than that of the control group.
The effect of exogenous spraying transpiration regulator on the accumulation of Cd in M. jalapa L. is shown in Fig. 1. Exogenous spraying of different concentrations of Glc did not significantly influence Cd enrichment in the roots of M. jalapa L. (P > 0.05), but it notably facilitated Cd accumulation in the stems and leaves (P < 0.05). Specifically, the T2 treatment with Glc significantly enhanced the BCF, TF, and Cd accumulation in the leaves (P < 0.05). Cd enrichment in leaves increased by 138.6% compared with the control group. The BCF and TF was 2.4 and 2.2 times that of the control treatment, respectively. Moreover, the T2 Glc treatment significantly improved the removal rate of soil Cd by M. jalapa L. (P < 0.05); the removal rate was 2.35 times that of the control treatment. These findings suggest that Glc, despite its nonsignificant direct enrichment effect on Cd, may indirectly enhance the removal efficiency of Cd through mechanisms such as promoting plant growth. In contrast, the application of different concentrations of FA did not significantly affect the Cd enrichment in the roots and leaves of M. jalapa L. (P > 0.05) and had no significant effect on the BCF and TF (P > 0.05). However, the T1 treatment with FA significantly increased the Cd enrichment in the stems of M. jalapa L. (P < 0.05). This indicates that although FA generally did not alter Cd enrichment patterns, a specific concentration (T1) had a distinct effect on stem Cd accumulation, increased by 46.6% compared with the control treatment.
Citation: HortScience 60, 5; 10.21273/HORTSCI18355-24
The influence of exogenous Glc and FA applications on the antioxidant enzyme activity and MDA content in M. jalapa L. leaves are shown in Fig. 2. The exogenous application of Glc could significantly increase the activities of CAT and POD in the leaves (P < 0.05). Among them, the POD activity of T2 treatment increased by 58% compared with the control, and the CAT activity of T3 treatment increased by 19% compared with the control treatment. Notably, as the concentration of Glc increased, the POD activity in the T3 treatment was significantly reduced compared with the T2 and T1 treatments (P < 0.05). Additionally, Glc application significantly decreased the MDA content in the leaves (P < 0.05); the MDA content of T2 treatment was 29% of the control treatment. The activity of SOD also varied with increasing Glc concentrations, with the T3 treatment exhibiting significantly lower SOD activity than the T1 and T2 treatments (P < 0.05).
Citation: HortScience 60, 5; 10.21273/HORTSCI18355-24
Furthermore, the exogenous application of FA impacted the antioxidant enzyme activity and MDA content in M. jalapa L. leaves. FA application significantly increased CAT activity (P < 0.05), and the T2 treatment increased by 21% compared with the control treatment. The low concentration T1 treatment notably reduced MDA content in the leaves (P < 0.05), MDA content was 15% of the control treatment. The activity of SOD in response to FA treatments was also concentration-dependent, with the T1 treatment showing significantly lower SOD activity compared with the control, whereas the T2 treatment exhibited significantly higher SOD activity than T1 (P < 0.05), it increased by 13%. Moreover, FA application significantly enhanced POD activity (P < 0.05). Among them, T1 treatment increased by 64% compared with the control treatment. It indicating that FA can modulate the antioxidant response in M. jalapa L. leaves, potentially contributing to the plant’s tolerance to environmental stressors.
The effect of exogenous spraying Glc on photosynthetic pigment content in leaves of M. jalapa L. is shown in Table 2. Exogenous Glc could significantly increase the content of chlorophyll a, but the content of chlorophyll b decreased significantly (P < 0.05). The content of chlorophyll a in T3 treatment increased by 67% compared with the control treatment, whereas chlorophyll b decreased by 36%. The treatment of T2 and T3 significantly increased carotenoid content and chlorophyll a/b value (P < 0.05). Exogenous FA could significantly increase chlorophyll a content, carotenoid content, and chlorophyll a/b value (P < 0.05). Further, T1 treatment increased chlorophyll a content, carotenoid content, and chlorophyll a/b values by 66%, 49%, and 125% compared with the control treatment, respectively. However, the chlorophyll b content decreased by 29%. The effect of exogenous Glc on the photosynthetic parameters of M. jalapa L. is shown in Fig. 3. Application of Glc at varying concentrations significantly enhanced the Pn of M. jalapa L. leaves (P < 0.05). Among them, T1 and T2 were 1 and 3.1 times higher than the control treatment, respectively. Concurrently, the Gs and E of the leaves increased significantly with increase of Glc concentrations (P < 0.05). Notably, the T1 treatment exhibited a significantly lower Gs and E compared with the control group (P < 0.05), decreased by 17% and 3% compared with the control treatment, respectively. The T3 treatment demonstrated significantly higher values than other treatments (P < 0.05). Compared with the control group, Gs and E were increased by 43% and 80%, respectively. Additionally, exogenous Glc significantly reduced the Ci in the leaves (P < 0.05), suggesting a positive influence on photosynthetic efficiency.
Citation: HortScience 60, 5; 10.21273/HORTSCI18355-24
The effect of exogenous FA on Pn at different spraying concentrations. At low concentration T1, there was no significant effect on Pn (P > 0.05), whereas at T2 and T3, Pn of M. jalapa L. was significantly increased (P < 0.05), 154% and 161% compared with the control group, respectively. Ci value was significantly reduced (P < 0.05). Among them, T3 treatment was only 53% of the control treatment. This indicates an inverse relationship between Pn and Ci under FA treatments. Furthermore, the Gs and E values were significantly elevated at the low concentration of T1 (P < 0.05), whereas these values were significantly diminished under the T2 and T3 treatment conditions (P < 0.05). These findings highlight the differential responses of photosynthetic parameters to varying concentrations of FA, with potential implications for the regulation of gas exchange and water use efficiency in M. jalapa L.
The effect of exogenous Glc on chlorophyll fluorescence parameters of M. jalapa L. is shown in Fig. 4. T1 treatment significantly increased Yield, ETR, and qP (P < 0.05), whereas T2 and T3 had no significant difference compared with the control (P < 0.05). Among them, yield increased 1.1 times in T1 treatment compared with the control treatment. The nonphotochemical quenching coefficient qN was significantly decreased in T3 treatment (P < 0.05), reduced by 3% compared with the control treatment. Exogenous FA (T3) significantly increased yield, ETR, and qP (P < 0.05), compared with the control group, these increased by 40.7%, 40.6%, and 48.7%, respectively. qN was significantly decreased (P < 0.05), with a decrease of 10.4% compared with the control treatment.
Citation: HortScience 60, 5; 10.21273/HORTSCI18355-24
Pearson coefficient was used to analyze the correlation between transpiration regulator and photosynthesis related parameters and Cd enrichment as shown in Fig. 5. The removal rate of Cd had a significant positive correlation with Pn and a significant negative correlation with Ci. Pn was significantly positively correlated with Chl a, BCF, TF, and E. MDA content and SOD activity were significantly negatively correlated with Pn, while POD activity was significantly positively correlated with Pn. Correlation analysis showed that there was a significant positive correlation between transpiration regulator and plant enzyme activity, and there was a significant positive correlation between Cd removal rate and transpiration regulator.
Citation: HortScience 60, 5; 10.21273/HORTSCI18355-24
Sugars play important roles in regulating plant growth, development, and stomatal movement (Li et al. 2018a), and the FA can promote plant growth, improve the plant stress resistance, increase production, and improve quality (Sun et al. 2020). This study investigated the effects of exogenously applied transpiration regulators, specifically Glc and FA, on the growth, biomass, and Cd uptake in M. jalapa L. The findings indicate that Glc enhances the growth and biomass accumulation of M. jalapa L. Studies have found that mesophyll-derived Glc is an important metabolite that connects stomatal movement and photosynthesis (Sabrina et al. 2020). Cd presence decreased plant growth, biomass and chlorophyll concentrations (Farid et al. 2015). In the context of phytoremediation efficiency, the results consistent with previous research, demonstrating a significant positive correlation between plant heavy metal content and transpiration rate. There was a significant positive relationship between the shoot Cd concentration and leaf transpiration in P. americana (Liu et al. 2010). The exogenous application of 4% Glc increased the Cd content in leaves of M. jalapa L. by 138%. However, the 0.1% FA application resulted in increase the Cd content in the roots of M. jalapa L. by 17%. Glc facilitates the transport of Cd from roots to shoots by increasing transpiration, whereas FA, by reducing the transpiration rate, leads to greater Cd accumulation in the roots. The application of exogenous Glc has been shown to increase the transpiration rate significantly in plants (Sami and Hayat 2019) and plays a significant role in the absorption of Cd by Phytolacca americana L. (Liu et al. 2010). Furthermore, exogenous Glc can reduce the content of MDA content in plant leaves, promoting plant growth and increasing biomass (Sami and Hayat 2019; Singh et al. 2014). Excessive heavy metals can reduce plant stomatal conductance, inhibit photosynthesis, induce excessive reactive oxygen species (ROS) production, disrupt plant redox balance, significantly affect plant physiological and biochemical functions, and inhibit its growth rate (Zhang et al. 2020). Our results indicate that Glc and FA can significantly enhance the phytoremediation potential of M. jalapa L. by increasing growth, biomass, and cadmium accumulation. This is in line with previous studies that have shown the potential of using plants to extract heavy metals from contaminated soils (Ashraf et al. 2019). In this study, Glc treatment was found to enhance the antioxidant enzyme activity in plants, alleviate oxidative stress, and facilitate the absorption and enrichment of heavy metals by plants. These findings underscore the potential of Glc as a transpiration regulator to improve phytoremediation strategies for heavy metal contaminated environments.
This study investigated the effects of exogenous Glc and FA on the antioxidant enzyme system and oxidative stress tolerance in M. jalapa L., with a focus on their regulatory roles in plant transpiration. Specifically, Glc optimizes the activity of SOD, indicating that appropriate concentrations can bolster the antioxidant defenses of plants. The application of FA significantly increased CAT activity and decreased MDA content, demonstrating its potential to improve the plant antioxidant. By increasing the activity of antioxidant-related enzymes and reducing MDA levels, these treatments help regulate the plant’s antioxidant defense mechanisms under heavy metal stress, thereby mitigating the detrimental effects of heavy metals (Rai et al. 2023). However, the efficacy of Glc and FA in enhancing phytoremediation could be influenced by various factors such as soil type, pH, and the presence of other competing ions. Our study was conducted under controlled conditions, and further research is needed to validate these findings under different environmental stressors and in diverse soil conditions. Additionally, the long-term effects of glucose and fulvic acid application on soil health and microbial communities require further investigation.
Exogenous Glc treatment has been shown to enhance the antioxidant enzyme activity in plants (Huang et al. 2013), and it also improves the antioxidant capacity of wheat under salt stress (Hu et al. 2012). The results of this study indicate that Glc significantly increased CAT and POD activities and decreased MDA content in the leaves of M. jalapa L. This increase in antioxidant enzyme activity aids in reducing oxidative stress and facilitates the absorption and enrichment of heavy metals by plants (Wu et al. 2013). Exogenous application of FA significantly increased CAT activity and decreased MDA content. Rational application of FA has been shown to significantly increase the yield of maize, wheat, and cucumber (Li et al. 2018b; Lu et al. 2019; Yan et al. 2019). Similarly, the foliar application of plant growth regulators (PGRs) improves the phytoremediation efficiency of heavy metals by Sedum alfredii Hance in contaminated soil (Chen et al. 2024). PGRs notably enhanced the antioxidant system in S. alfredii by increasing the activities of SOD, CAT, and POD, while also reducing lipid peroxidation as indicated by decreased MDA content. This consequently improved the tolerance to heavy metals and promoted the growth of S. alfredii (Chen et al. 2024). Several studies have demonstrated that exposure to Glc results in increased chlorophyll content and elevated activities of SOD, CAT, and POD. Additionally, exogenous Glc has been found to decrease the levels of MDA in Brassica juncea (Sami and Hayat 2019). In this experiment, FA treatment (T2) significantly increased the Pn but reduced the E, whereas Glc spraying promoted photosynthesis but decreased the ETR and increased the E. There have pharmacological data showed that Glc-induced stomatal closure was greatly inhibited by CAT (Li et al. 2018a). Glc spraying also reduced the qP of M. jalapa L. and increased the qN, whereas FA increased the qP at low concentrations and decreased the qN. It has been shown that low concentrations of FA can promote photosynthesis, whereas high concentrations have a strong inhibitory effect (Ma et al. 2011). In this experiment, it was found that 0.2% FA spraying significantly increased the Pn, reduced MDA content, and enhanced plant tolerance to Cd stress. Studies have revealed that GCSC1 influences the accumulation of ROS in guard cells by regulating calcium content in chloroplasts, leading to changes in stomatal opening and transpiration rate (Liu et al. 2024). Glc and FA treatments significantly increased the Pn of M. jalapa L. Changes in leaf morphology can affect photosynthesis, as the size, shape, and structure of leaves directly influence light absorption and the diffusion path of carbon dioxide (Hao et al. 2022). In our study, although leaf morphology changes were not directly measured, it can be speculated that under high concentrations of fulvic acid, any changes in leaf morphology could potentially affect the efficiency of photosynthesis. Chen et al. (2022) investigated the impact of FA on the growth and photosynthetic properties of lettuce (Lactuca sativa L.) under Cd stress, finding that FA could stabilize the photosynthetic machinery and maintain high rates of photosynthetic carbon assimilation. This indicates that FA has a positive effect on photosynthesis under certain conditions, which is consistent with our observation. However, with the increase of spraying concentration, photosynthesis cannot be continuously improved, which may be related to many factors. At the same time, it also emphasizes the necessity of further study on the complexity of the physiological effects of FA on plants. These findings contribute to the understanding of how transpiration regulators affect plant photosynthesis and transpiration. The application of Glc as a transpiration promoter on plant leaves, although not significantly affecting the growth index of M. jalapa L., significantly increased the removal rate of Cd, Pn, and POD activity and significantly reduced the content of MDA, a marker of lipid peroxidation in leaf cell membranes. Thus, the appropriate concentration of Glc can promote the enrichment of Cd in M. jalapa L. and alleviate oxidative stress caused by Cd. These results offer a new perspective on the use of transpiration regulators to enhance phytoremediation efficiency and provide a potential application strategy for the remediation of cadmium-contaminated soil. Transpiration rate was significantly positively correlated with shoot Cd concentration and total Cd uptake of different rapeseed varieties (Gao et al. 2010). The transfer of Cd from the xylem to the leaves in tobacco plants is primarily driven by transpiration (Liu et al. 2016). Glucose providing a carbon source for starch accumulation and facilitating light-induced stomatal opening which was essential for plant growth (Sabrina et al. 2020). One limitation of our study is that artificially contaminated soil may not fully capture the complex interactions between soil components, which could influence the uptake of cadmium by plants. Future research should focus on conducting field experiments under various natural soil conditions in environments that are naturally polluted. This is essential for understanding the ecological impact of enhanced phytoremediation measures. Additionally, future studies should further explore the specific effects of varying concentrations of Glc and FA on the antioxidant system of M. jalapa L. and how these effects relate to plant growth, development, and environmental adaptability. Studying the impact of these transpiration regulators under different environmental conditions is also crucial for optimizing the application of plant growth regulators and improving plant stress resistance.
This study investigated the effects of exogenously applied transpiration regulators Glc and FA on the growth, biomass production, and Cd accumulation in M. jalapa L. The findings revealed that Glc, functioning as a transpiration promoter, significantly enhanced the growth and biomass accumulation of M. jalapa L. A significant positive correlation was observed between the plant’s heavy metal content and its transpiration rate. Glc facilitated the translocation of Cd from roots to shoots by increasing transpiration, whereas FA contributed to greater Cd accumulation in roots by inhibiting transpiration. The BCF and TF was 2.4 and 2.2 times that of the control treatment at 4% Gls spraying, respectively. The removal rate was 2.35 times that of the control treatment at 4% Gls spraying. The application of Glc notably elevated the transpiration rate of M. jalapa L., thereby increasing the Cd content in leaves, providing an effective way to improve the removal rate of Cd by plants. Both Glc and FA bolstered the antioxidant enzyme system of M. jalapa L., improving its tolerance to oxidative stress and environmental challenges. The POD activity increased by 58% compared with the control at 4% Gls spraying. However, FA application significantly increased CAT activity and decreased MDA content, indicating its potential to enhance plant antioxidant capacity. It was found to increase Cd retention in roots by 17% and improve photosynthesis and chlorophyll content of exogenously applied FA. In summary, although exogenous spraying of Glc had no significant effect on the growth index of M. jalapa L., it significantly increased the removal rate of Cd, Pn, and POD activity of M. jalapa L. and significantly reduced MDA content. The application of 4% Glc to the leaves can promote Cd enrichment in M. jalapa L. and mitigate the oxidative stress induced by Cd. These results underscore the potential of using Glc to optimize phytoremediation strategies for Cd-contaminated soils. Future research should further explore the specific mechanism of different transpiration regulators on the antioxidant system of M. jalapa L. and how these effects are related to plant growth, development, and environmental adaptability. This knowledge is crucial for optimizing the application of plant growth regulators and enhancing plant stress resistance. It is also crucial to develop a standardized protocol for using various combinations of transpiration regulators to broaden their applications and enhance their effectiveness.
Effect of exogenous glucose and fulvic acid on accumulate cadmium Cd of Mirabilis jalapa L. Vertical bars represent standard deviation of the means (n = 3). The uppercase letters show the statistical difference in determined indexes among different treatments of fulvic acid, and the lowercase letters indicate the difference in determined indexes among different treatments of glucose. The same letter indicates no significant difference at α = 0.05 level.
Effect of exogenous glucose and fulvic acid on antioxidative enzyme activities and MDA content of Mirabilis jalapa L. Vertical bars represent standard deviation of the means (n = 3). The uppercase letters show the statistical difference in determined indexes among different treatments of fulvic acid, and the lowercase letters indicate the difference in determined indexes among different treatments of glucose. The same letter indicates no significant difference at α = 0.05 level.
Effect of exogenous glucose and fulvic acid on photosynthetic parameters of Mirabilis jalapa L. Vertical bars represent standard deviation of the means (n = 3). The uppercase letters show the statistical difference in determined indexes among different treatments of fulvic acid, and the lowercase letters indicate the difference in determined indexes among different treatments of glucose. The same letter indicates no significant difference at α = 0.05 level.
Effect of exogenous glucose and fulvic acid on chlorophyll fluorescence parameters of Mirabilis jalapa L. Vertical bars represent standard deviation of the means (n = 3). The uppercase letters show the statistical difference in determined indexes among different treatments off acid, and the lowercase letters indicate the difference in determined indexes among different treatments of glucose. The same letter indicates no significant difference at α = 0.05 level.
Correlation analysis of transpiration regulator on photosynthesis and antioxidant enzymes of Mirabilis jalapa L.
Contributor Notes
Effect of exogenous glucose and fulvic acid on accumulate cadmium Cd of Mirabilis jalapa L. Vertical bars represent standard deviation of the means (n = 3). The uppercase letters show the statistical difference in determined indexes among different treatments of fulvic acid, and the lowercase letters indicate the difference in determined indexes among different treatments of glucose. The same letter indicates no significant difference at α = 0.05 level.
Effect of exogenous glucose and fulvic acid on antioxidative enzyme activities and MDA content of Mirabilis jalapa L. Vertical bars represent standard deviation of the means (n = 3). The uppercase letters show the statistical difference in determined indexes among different treatments of fulvic acid, and the lowercase letters indicate the difference in determined indexes among different treatments of glucose. The same letter indicates no significant difference at α = 0.05 level.
Effect of exogenous glucose and fulvic acid on photosynthetic parameters of Mirabilis jalapa L. Vertical bars represent standard deviation of the means (n = 3). The uppercase letters show the statistical difference in determined indexes among different treatments of fulvic acid, and the lowercase letters indicate the difference in determined indexes among different treatments of glucose. The same letter indicates no significant difference at α = 0.05 level.
Effect of exogenous glucose and fulvic acid on chlorophyll fluorescence parameters of Mirabilis jalapa L. Vertical bars represent standard deviation of the means (n = 3). The uppercase letters show the statistical difference in determined indexes among different treatments off acid, and the lowercase letters indicate the difference in determined indexes among different treatments of glucose. The same letter indicates no significant difference at α = 0.05 level.
Correlation analysis of transpiration regulator on photosynthesis and antioxidant enzymes of Mirabilis jalapa L.
