Effect of Heavy Metals Zn and Cu on Growth Parameters of Lycopersicum esculentum

Many agricultural regions of the world soils have used for agriculture that are moderately polluted with heavy metals such cadmium (Cd), copper (Cu), zinc (Zn), nickel (Ni), cobalt (Co), chromium (Cr) and arsenic (As) (Proshad  et al., 2019). The digestive system of basic components may be aggravated by the prolonged use of phosphatic fertilizers, the application of sewage slime, dust from smelters, industrial waste and odd watering techniques (Sivaranjanee et al., 2022). A vital component of the natural environment, soil is altered by agricultural and industrialized human activities, increasing soil erosion and degrading soil fertility (Paul et al., 2021).
       
Heavy metals like Zn and Cu are necessary for healthy plants development and growth because they are essential parts of multiple enzymes and other proteins. However, large levels of both unneeded heavy metals in the soil can have detrimental impacts on most plants, including limiting their ability to grow (Wang et al., 2018).
       
High concentration of heavy metals, such Cu and Zn, are toxic and harmful for plant growth (Arif et al., 2016), (Mir et al., 2021), as plants absorb them rapidly when growing in a growing medium like soil. Cu and Zn have harmful effects on several plant functions, including respiration and photosynthesis. They also cause a reduction in the absorption of water and micronutrients by plants.
       
Micronutrients of agriculture medium such as zinc and copper are required in small amount in plants for a verity of physiological and biochemical functions as well as for development (Ferreira et al., 2018). Toxic levels of these metals resulted in chlorosis, necrosis and root portions (Małkowski et al., 2019), as well as photosynthesis inhibition and permeability of the plasma layer.
       
The tomato (Lycopercicum esculentum) crop belongs to the Solanaceae family. Tomatoes are among the most important agriculture products in the world (Marti et al., 2018), but they can become less productive due to a range of abiotic stressor, such as heavy metals (Gerszberg and Hnatuszko-Konka, 2017) and biotic stresses (Bouzroud et al., 2018), (Quiterio-Gutiérrez  et al., 2019). Utilizing its surface shape and functional groups, the mechanism of metal removal property allows tomato plant roots to absorb heavy metals and distribute them throughout the plant (Jiraungkoorskul et al., 2016). Since tomatoes are a highly profitable product in many places where they produced in fields or greenhouse, they have been farmed and genetically modified for a long time. Although consumer can still get illnesses from it, the main cause of excessive quantities of metals and chemical pesticides that are used on the produce comes from greenhouses (Ines and Bernacchia, 2018). On the other hand, an excess of these compounds pollutes soil, negatively impacts agricultural soil’s microflora and microfauna and lowers the quality of tomato plants. On the other hand, a variety of plant security concerns are linked to tomatoes (Badiaa et al., 2020).
       
The body loses iron (Fe), vitamin C and other essential vitamins when it consumes food tainted with heavy metals (Carolina  et al., 2019). Lack of these essential supplements results in resistance problems, impedes intrauterine development, damages psycho-social abilities and leaves people without healthy sustenance-related impairments (World Health Organization  et al., 2016).

Culture condition
 
This research was conducted in the of laboratory at Department of Chemistry, Ewing Christian College, Prayagraj in presence of sunlight. After being properly cleaned with distilled water and disinfected with a 20% (v/v) hydrogen peroxide solution, tomato (Lycopercicum esculentum) seeds were allowed to grow in petri plates coated with filter paper that had been moistened with distilled water. At a temperature of 22±3^oC, germination took place in the dark. Seedlings were then subcultured after five days. The 28 x  30 (height x diameters in cm) clay pots were filled with compost and regular soil in a 5:1 ratio. Three pots were used as replicates for each concentration treatment, including the control group (Al Mamun et al., 2021). After a 15-day culture interval, the plants had been transferred into pots containing heavy metals (Zn; 50, 70 and 90), Cu (40, 60 and 75) and control.
 
Physiological parameters
 
At three different time intervals, such as 18, 36 and 54 DAS, the effects of heavy metals on plant physiological parameters, such as shoot length, number of leaves, root length, number of branches, number of fruit, leaf area index, plants dry weight, relative growth rate, percentage moisture, biomass accumulation and chlorophyll content, were measured.
 
Leaf area index
 
Plant canopies are characterized by a dimensionless number called the leaf area index (LAI). It is defined as the number of square meters of green leaf area on one side of a broadleaf canopy per unit of ground surface area (Fang et al., 2019).
 

  

 
Chlorophyll content
 
The method used to determine chlorophyll was based on the amount of light that an 80% aqueous acetone extract of chlorophyll could absorb (Amin  et al.,  2018). The density of 80% acetone chlorophyll extract was measured in a 10 mm cell using a spectrophotometer at 663 and 645 mµ. Simultaneous equations were then created using the unique absorption coefficients for chlorophyll a and b. This allowed for the calculation of the levels of chlorophyll a and chlorophyll b.
 
Chlorophyll a = 12.7A₆₆₃-2.69A₆₄₅
 
Chlorophyll b = 22.9A₆₄₅-4.68A₆₆₃
 
Total Chlorophyll = Chlorophyll a + Chlorophyll b
 
Where
A₆₄₅= Absorption at a wavelength of 645 nm.
A₆₆₃= Absorption at a wavelength of 663 nm.
 
Plant sampling
 
At 18, 36 and 54 DAS, tomato plants (whole plants with roots) were properly removed from clay pots  that was evaluated. Separately, every tomato sample was placed in a clean porcelain crucible and properly cleaned with distilled water. Every plant’s leaves, roots, shoots and fruits were separated, dried in an oven for 48 hours at room temperature or at 40oC for 24 hours and samples were then crushed into a powder after being placed in little paper bags for further analysis.
 
Chemical analysis
 
The atomic absorption spectrophotometer (AAS) method was also used to measure the total concentrations of Zn and Cu in the plant samples. The diacid solution (HNO3-H2SO4) was prepared and used to estimation of Zn and Cu (Sbartai et al.,  2017). The 1 g plant sample was predigested with 5 ml diacidand kept for over night. After, again10 ml diacid was added and slowly heated on a hot plate for 30- 40 minutes till a clear supertant was observed. The extract was filtered through Whatman-42 filter paper and make up final volume 50 ml with distilled. Measured the metal concentration in solution with AAS at Zn 213.86 nm and Cu 324.75 nm wavelength.

The present study aims to examine how zinc and copper affect several morphological and physiological characteristics of Lycopercicum esculentum and compare these effects to those seen in plants under control. In order to provide awareness on these micronutrients’ function in plant health and development, the study intends to assess how supplementing them affects the development of plants and physiological features.
 
Parameter
 
Impacts of Zn and Cu on growth parameters, Leaf Area Index, Relative Growth Rate, %Moisture and Chlorophyll Content compare to controlled plants are given in Table 1 and Table 2.

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Chlorophyll content
 
The maximum chlorophyll content is showed in control plants (Table 1, 2), as the concentration of both heavy metals increases the chlorophyll content declines. Zinc and copper treatment dramatically lowered the leaf chlorophyll content compared to control plants. Chlorophyll contents of all concentrations of Zn and Cu at times 18, 36 and 54 days after sowing are given in Table 1, 2. 
 
Heavy metal concentration in different parts of tomato plants
 
Heavy metals concentration (Zn and Cu) in different parts of tomato plants are presented in Table 3 and 4 at 18, 36 and 54 days after sowing.

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The results showed (Table 1 and 2) that Zn and Cu attention had a substantial impact on plant development after 18, 36 and 54 days after sowing. The outcome demonstrates that the photosynthesis of L. esculentum and contaminants treatment by both element growth parameters was adversely correlated with the soil. Research has confirmed that Zn and Cu have a detrimental effect on tomato plant development (Rachid, 2022). The high Zn and Cu concentrations considerably reduced the plants’ height, fresh weight, number of leaves, number of roots and thickness of the shoots when compared to the control plants.
       
The results of this study indicate that higher concentrations of Cu may have more negative effects. Increased copper levels affect the structure of proteins, interfere with the photosynthetic process and enzyme activity and change the permeability of plasma membranes (Hou et al., 2017). Furthermore, high Zn concentrations can hinder plant growth and development by disrupting antioxidant defense systems, metabolic processes and mineral intake and distribution in an unbalanced manner (Hamzah Saleem  et al., 2022). Cu and Zinc’s toxicity to plants depend upon multiple factors, such as the resistance or sensitivity of the plant species, the total amount of heavy metal absorbed and threshold level that the species can tolerate. The result of this study showed that at 18, 36 and 54 days after sowing, the concentration of harmful levels of heavy metals Zn and Cu in tomato plant root were higher than other parts of plants. The finding of this study suggest that mechanism that restrict or prevent these elements from the root to other parts of tomato plants are not entirely avoided because high concentration of zinc and copper are harmful to plant metabolism particularly in photosynthesis and as a cofactor for protein antioxidant. The presence of heavy metals and their addition to the soil had an adverse effect on the leaf area index. Higher light interception and thus higher gross photosynthesis are the outcomes of increased LAI. Since there is more leaf number when the LAI is greater, more conservation respiration is required, which in turn indicates a bigger biomass. However, in the model, crop metabolic activity, which is measured by the crop’s relative growth rate (RGR), determines specific conservation respiration, or respiration per unit biomass. Higher biomass lowers RGR and, hence, conservation per unit biomass at the same growth rate. Since neither gross photosynthesis nor crop conservation significantly alter at a LAI of 4, there is no obvious optimal LAI (Farzadfar et al., 2017).
       
The amount of chlorophyll in tomato leaves exposed to high zinc concentrations was found to be lower than in the control, which is consistent with the findings of (Nazir et al., 2019; Turhan, 2021; Wang et al., 2018) regarding the regular a decline of carotenoids and chlorophyll in plants exposed to varying levels of heavy metals. Heavy metal buildup causes electrochemically generated oxidative damage, disruption of membrane function and other issues (Sbartai et al., 2017). Conversely, in low amounts, zinc promotes the formation of chlorophyll.

According to the study’s results, lycopercicum esculentum’s physiological and morphological parameters are negatively impacted by increased Zn (70 and 90 mg) and Cu (60 and 75 mg), which eventually causes growth suppression and metabolic disruption. Excessive levels of heavy metals, such as copper (Cu) and zinc (Zn), might interfere with a plant’s ability to absorb nutrients and thrive. All measured growth metrics decreased as Zn and Cu concentrations rose, suggesting that they harmed plant health. Although zinc and copper are necessary minerals, high concentrations harm plant metabolism, highlighting the necessity of applying them sparingly in agricultural operations.

I sincerely thank Ewing Christian College, Prayagraj, for providing research apparatus and UV-Visible Spectroscopy. Special gratitude to my supervisor and coauthor for their invaluable support and guidance throughout this study.
 
Disclaimers
 
He views and conclusions expressed in this article are solely those of the authors and do not necessarily reflect the views of their affiliated institutions. The authors are responsible for the accuracy and completeness of the information provided, but do not accept any liability for any direct or indirect losses arising from the use of this content.

The authors declare that there are no conflicts of interest related to this research article. All authors have no financial or personal relationships that could have influenced the work presented in this study.