Si NPs increase the biomass of the plant's maize and increase the growth of plants by reducing the stress of HMs (Tripathi et al. 2017). HMs present over all the world and show a different impact on human life by contaminating the process. HMs are non-degradable metals that stop the growth of plants because that is highly toxic metals. Metals have shown their impact on plants, animals, and human life (Khan et al., 2021; Zhang et al., 2014). The Si NPs are non-toxic partials that increase the silicon level in plants under heavy metal stress. Increasing the Si NPs treatment increase the growth of maize plants. The silicon increased the length of root and length of shoot under the stress of Cd. This experiment result showed an improvement in the plant's growth parameters. The Si NPs increase the quantity of silicon in the plants and increases the Si-ions concentration in the plants due to this plant growth is promoted. This finding is supported by (Hossain et al. 2021).
The experiment result showed that the length of maize shoot was decreased under Cd stress. The Cd is a heavy metal that reduces the growth of maize plants by the accumulation in the cell vacuole and stops slow the activity of the cell. The treatments of Si NPs have increased the length of the shoot. This current finding is supported by Abd El-Mageed et al., (2020), who stated that the Si NPs treatments significantly improved the length of maize roots under Cd stress conditions. Cd reduces the growth of shoot (Seregin et al. 2004). The Si NPs improved the nutrients uptake by treatment of Si NPs. Results showed that the highest shoot length was noted in the treatment where Si NPs were applied at the rate of 400 ppm while the lowest shoot length was noted in treatment where no Si NPs were applied. Different levels of Cd stress significantly affect the shoot length of maize. The maximum shoot length was recorded where Cd was not applied such as in the control treatment while the lowest shoot length was noted in treatments where Cd was applied at the rate of 30ppm. The silicon provided the silicon to the plant to increase the growth and reduce the effect of HMs ( Rastogi et al. 2019). Under the stress of Cd, the maize plant increased the length of its roots to absorb nutrients in high quantities to reduce the Cd stress. The Si NPs increased the root and shoot length. This current finding is supported by (Siddiqui et al. 2020)., who stated that the Si NPs treatments significantly enhanced the root and shoot length under Cd stress conditions.
The highest root fresh weight was noted in the T4 treatment where Si NPs were added at the rate of 400 ppm while the lowest root fresh weight was recorded in treatment where no Si NPs were applied. Different levels of Cd stress significantly affect the root fresh weight of maize. Minimum fresh root weight was recorded where Cd was not applied such as in control treatment while the maximum root fresh weight was noted in treatments where Cd was applied at the rate of 30ppm. This current finding is supported by (Dresler et al. 2015), who stated that the Si NPs treatments significantly enhanced the root fresh weight under Cd stress conditions. The highest shoot fresh weight was noted in the T4 treatment where Si NPs were applied at the rate of 400 ppm while the lowest shoot fresh weight was noted in treatment where no Si NPs were applied. Different levels of Cd stress significantly affect the shoot of plant fresh weight of maize. In shoot fresh, the maximum weight was recorded where Cd was not applied such as control treatment while the minimum shoot fresh weight was noted in treatments where Cd was applied @ 30ppm. This current finding is supported by (Dresler et al. 2015), who stated that the Si NPs treatments significantly enhanced the shoot fresh weight under Cd stress conditions. Recorded data showed that Cd stress and different treatments of Si NPs as well as the interaction between Cd and treatments significantly affected the shoot dry weight of maize. The highest weight of dry shoot was recorded in the treatment where Si NPs were added in the foliar form at the rate of 400 ppm while the minimum weight of dry shoot dry was noted in treatment where no Si NPs were applied. Different levels of Cd stress significantly affect the shoot dry weight of maize. The maximum shoot dry weight was recorded where Cd was not applied such as in the control treatment while the minimum shoot dry weight was noted in treatments where Cd was applied at the rate of 30ppm. The current finding is supported by (Dresler et al. 2015). Under the Cd stress, the dry leaves' weight was decreased because Cd is a toxic substance that stops the activity then highest the length noted in the Si NPs treatment at the rate of 400ppm. The result showed that under the stress the maize plant extends its roots and increased the weight of the roots. Si NPs increased the weight of roots and shoot in maize plants. Results showed the weight of the root was increased under the Si NPs treatments.
Results show that the Si NPs under Cd stress showed an impact on the leaf pigments which are chlorophyll a, b, total chlorophyll contents, and carotenoids. The Si NPs treatment was applied at the rate of 400ppm increased the chlorophyll contents than the control group was no Si NPs applied. The Si NPs reduced the Cd stress and increased the chlorophyll-a content in the plant. The highest value of chlorophyll-a content was recorded where cd stress was not applied such as in control treatment while the lowest value of chlorophyll-a content was observed in cd treatment where cd was applied at the rate of 30 ppm. A change in the chlorophyll b contents was noted by the experiment. The Si NPs increased the chlorophyll b contents in the plants and were applied at the rate of 400ppm the control group. There is the highest concentration of chlorophyll b noted in the Si NPs treatment group. The Si NPs increased the photosynthetic process. Because they facilitate the uptake of essential nutrients by xylem to increase the chlorophyll b content. When the chlorophyll increased the process of photosynthetic was increased. The current finding is supported by (Khan et al. 2019). The Si NPs decreased the concentration of HMs that accumulate in the plant's body. In our result, the Si NPs treatments 400 ppm decreased the concentration of Cd and increase the chlorophyll contents (a and b) in maize. In maize plants, the Si NPs treatment under Cd showed the highest value of carotenoids were treatment added at the rate of 400 ppm of Si NPs. Then the lowest value was recorded where no silicon was added such as the control group. In 30 ppm Cd stress the Cd concentration decreased due to silicon treatment 400ppm then the control where no silicon was applied. The Si NPs increased the photosynthetic pigments under the stress of HMs such as Cd. The current result is supported by (Ling et al. 2017). The Si NPs showed an impact on the concentration of biochemicals such as soluble proteins, proline, soluble amino acid, and Soluble sugar. The result showed that the highest value of total soluble proteins noted was the Si NPs applied at the rate of 400 ppm then the control group. There is the lowest value of proteins noted where no silicon Si NPs applied. The proteins are the complex structure that showed an important role in the structure and function of cells. All the plant's enzymes are formed by proteins. The Cd reduced the protein concentration in the plants then reduced the growth of plants. The result showed the Si NPs increased the proteins and decreased the Cd level. The Cd decreases the synthesis of proteins and reduces the work of proteins. The NPS increased the Si concentration in the plant. Si act as a barrier responsible to repaired and decreasing the injury of the cell membrane. The results are similar to the findings of (Khan et al. 2019).
The proline showed an important role in plants. The proline protects the plant against Cd stress. When Cd stress occurs the proline act as a barrier and reduced the Cd stress to promote plant growth. There is the highest value of total proline was recorded in the treatment where Si NPs were applied at the rate of 400 ppm while the lowest value of total proline was noted in treatment where no Si NPs were applied. Different levels of Cd stress significantly affect the total proline of maize (Hayat et al. 2012). The maximum value of total proline was recorded where Cd was not applied such as in control treatment while the lowest value was noted in treatments where Cd was applied at a high rate. The maize plant showed a high level of amino acids in Si NPs treatment. The highest level of amino acid was noted where a high level of Si NPs applied then control where no treatment was applied. The Cd reduced the amino acid concentration. Reduction in the amino acid reduced the protein level. The result shows that the highest level of amino acid noted was no Cd applied than the Cd stress. The amino acid shows an important role in the structure and function of the cell.
Si NPs increased the level of sugar in the plant. Sugar shows an important role in the plant. Sugar has a dual role in the plant. Sugar is involved in some important metabolic processes and is also responsible for signal-regulating genes involved in the photosynthesis process and sucrose metabolism. Results showed that the Si NPs increased the level of sugar in maize plants. Cd reduced the sugar by a reduction in uptake nutrients. The Si NPs under Cd stress increased the antioxidant concentration in the plant. The silicon produced by the Si nanoparticles increased the concentration of POD. The POD protected stress conditions. This study shows that in the Cd stress the value of POD was increased when increased the Si NPs treatment at the rate of 100 ppm to 400 ppm and decreased the concentration and uptake of Cd in stress conditions. In the result, the highest value of peroxidase dismutase was recorded in the treatment where Si NPs were applied at the rate of 400 ppm while the lowest value of peroxidase dismutase was noted in treatment where no Si NPs were applied. Different levels of Cd stress significantly affect the peroxidase dismutase of maize. The maximum value of peroxidase dismutase was recorded where Cd was not applied such as in the control treatment while the lowest value was noted in treatments where Cd was applied at the rate of 30ppm (Thind et al. 2021).
The Si NPs increased the CAT concentration. The CAT is an antioxidant enzyme. The CAT is present in all the plants. The CAT showed an important role in stress conditions when energy efficient. The CAT catalyzed the H2O2 molecules into O2 and H2O. As a result, the highest value of catalase was recorded in the treatment where Si NPs were applied at the rate of 400 ppm while the lowest value of catalase was noted in treatment where no Si NPs were applied. Different levels of Cd stress significantly affect the catalase of maize. The maximum value of catalase was recorded where Cd was not applied such as in the control treatment while the lowest value was noted in treatments where Cd was applied at the rate of 30ppm. The concentration of CAT is increased by the nanoparticle’s treatment (Lukačová et al. 2013). The Si NPs treatment increased the APX (Antioxidant enzyme Ascorbate peroxidase) concentration in maize leaves under Cd stress. As a result, the highest value of ascorbate peroxidase was recorded in the treatment where Si NPs were applied at the rate of 400 ppm while the lowest value of ascorbate peroxidase was noted in treatment where no Si NPs were applied. Different levels of Cd stress significantly affect the ascorbate peroxidase of maize. The maximum value of ascorbate peroxidase was recorded where Cd was not applied such as in the control treatment while the lowest value was noted in treatments where Cd was applied at the rate of 30ppm. The APX is increased by the Si NPs under the stress of Cd (Thind et al. 2021).
The SOD is an enzyme found in all living plant cells. This is responsible for the speed of chemical reactions and speeds up the chemical reaction in the cells. The SOD breakdown the harmful molecules in the cell to prevent cell damage under stress conditions in the experiment result the highest value of superoxide dismutase was recorded in the treatment where Si NPs were applied at the rate of 400 ppm while the lowest value of superoxide dismutase was noted in treatment where no Si NPs was applied. Different levels of Cd stress significantly affect the superoxide dismutase of maize. The maximum value of superoxide dismutase was recorded where Cd was not applied such as in the control treatment while the lowest value was noted in treatments where Cd was applied at the rate of 30ppm. The concentration of SOD was increased by the Si NPs treatment under Cd stress. Results showed that the maximum Cd value present in leaves and roots under the stress of Cd where Cd was added @ 30 ppm while beneath average conditions such a control group. The minimum value of Cd in leaves and roots was recorded under the treatment of Si NPs. Different levels of Si NPs that were applied in the form of foliar spray highly significantly exaggerated the Cd in leaf and root of maize and showed that more Cd contents in leaves and roots were noted in the controlled group in which foliar Si NPs were not applied while the lowest value of Cd content in leaves and roots was recorded where the Si NPs foliar was applied in the form of foliar at 400 ppm in the stress conditions of Cd (Shafeeq-ur-Rahman et al. 2020).