A Conceptual Research Paper (Environmental Sciences)

Author: Aiman Afzal

laureatefolks@gmail.com

ABSTRACT:

Due to the scarcity of freshwater several farmers have started using contaminated water for the purpose of irrigation. The current study investigated the effect of lead bioaccumulation in a wheat cultivar named Cv. Shafaq-2006. The experimental analysis has consisted of 7 lead treatments for example 0 to1000mg lead/kilogram. It was revealed in results that Pb negatively impacted the parts of crop and severely decreases the fresh weight of seedling (− 74%), germination (−30%), dry weight of seedling (−77%), tolerance index (− 84%), root fresh weight (− 50%), plant height (− 33%), vigour index (− 89%), leaves number (− 41%), shoot dry weight (− 71%), fresh weight of shoot (− 62%), dry weight of root (− 63%), and length of root (− 45%). The physiological attributes also showed negative impacts such as transpiration rate (− 72%), stomatal conductance (− 82%) and rate of photosynthesis (− 74%). Correspondingly, biochemical parameters such as total chlorophyll, chlorophyll b, chlorophyll a and carotenoids also respond negatively like − 43, − 42, − 53 and −41 respectively. In T6 the attributes of yield like seed weight/plant, seed number/plant, the harvest index and 1,000 seed weight were decreased by 88%, 90%, 61% and 44% respectively. Besides, in the highest concentration of lead (T6) the contents of protein (− 81%), potassium (− 55%) and phosphorous (− 60%) were highly effected. In comparison to the control plant the accumulation of Lead was extremely higher (119%) in seeds. The bioaccumulation of Lead in parts of crop above threshold concentrations is a serious concern for human health.

1. INTRODUCTION:

In developing countries such as Pakistan the scarcity of freshwater is a major problem for agriculture. Presently, farmers have started using contaminated industrial wastewater to meet the requirements of water (Rezapour, et al., 2019). The wastewater discharged from industries contains large amount of toxic heavy metals for instance lead (Pb), cadmium (Cd), nickle (Ni), zinc(Zn), iron(Fe) and maganese(Mn) etc. These heavy metals (HM) bioaccumulate in different parts of crop and lead to several severe health concerns to ecosystem and human (Wang, et al., 2017). There are also several resources for the entry of heavy metals in the ecosystem such as industrial effluents, activities of mining, sludge use as manure and agronomic practices (Zhang, et al., 2018).Globally the contamination of heavy metals(HMs) causes a sharpe rise in problems of environmental and human health. The cultivation of crops near such polluted areas lead to the poor growth of crops and bioaccumulation of heavy metals(HMs) in crops. Howerever,the ingestion of these acccumulated HMs pose high risk to the health of livestock &humans (Khan, et al., 2013).

Zajac in their study investigated one hundred and ninety five toxic Site Identification Program sites in thirty three middle and low income countries and stated that almost 820,000 childbearing age women living at these areas have significant risk of lead exposure (Zajac, et al., 2020). Lead (Pb) is a significant persistent pollutant in the environment that has 150 to 1500 years retention time and ability to pose several negative impacts on human (Vergara, et al., 2020). Lead accumulates in plants through several means such as air, water and soil. The detrimental impacts of lead includes reduction in germination, interference in uptake of nutrients (Tiwari, et al., 2013), reduction in photosynthesis, mitosis inhibition in tip, disturbed respiration, (Rizwan, et al., 2017)delay in growth of plant (Shekar, et al., 2011), alternations in enzymatic activities, changes in metabolism, alternation in morphology of roots (Bergqvist, et al., 2014), inflamed vacuoles, injured thylakoid, expended plasmolysis and deformed nucleolus (Rafaqat, et al., 2015). HMs significantly affected the parts of crop by causing the formation of malondialdehyde and reactive oxygen species in excessive amount predominantly in mitochondria and chloroplast of root, leaves, and shoots (Basharat, et al., 2014). It is reported in the study by Rafaqat at el that the chromium toxicity in Brassica napus L. damages the ultra-structures of its roots. Besides, they are also responsible for altering the plant’s natural antioxidant enzymes (Gill, et al., 2014). The ROS (reactive oxygen species) are capable for attacking biomolecules and may cause death of cells. Therefore, the contamination of lead is a major problem for agriculture. In Pakistan wheat, rice, sugarcane and cotton are most significant cash crops that account 75% of total output. (Yang, et al., 2013) The main food crop of Pakistan is wheat. Farmers are utilizing industrial polluted water for irrigation due to the scarcity of water farmers for irrigation. Several chronic health impacts are caused by the presence of lead in food chain (Vaiserman, et al., 2016). The tolerance of metal in crops is improved by the utilization of plant growth regulator such as 5-aminolevulinic acid (Ali, et al., 2015). So, this study was executed and designed to examine the effects or impacts of lead on yield, growth of seedling, germination, mineral contents, biochemical and physiological parameters.

2. MATERIAL AND METHODS

2.1.Germination experiment:

Shafaq 2006 is a wheat cultivar that was chosen as test crop specie. This experiment was done in the growth room in 90mm petri dishes. Firstly proper washing and sterilization of petri dishes were done. Blotting paper was placed in all petri dishes and then after surface sterilization of twenty five seeds they were also placed in all petri dishes. Seven lead treatments named as T1, T2, T3, T4, T5, T6, T7 were prepared for irrigation by utilizing lead nitrate. Lead treatments have 0, 100, 200, 400, 600, 800 and 1,000mg Pb/L respectively.

Specie of Crop	Pb treatments	Seeds/petri dish	Replicates
1	7	25	4

Completely randomized design was used to place all these petri dishes and in each respective petri dish 2ml of lead treatment was added daily. As radical started emergence the readings of germination were noted. Data was collected for estimating length of plumule, percentage of germination, length of radical, fresh biomass and length of seedling. The estimation of both Tolerance index and Seedling vigor index were done by multiplying the length of seedling with percentage of germination. The Tolerance Index of metals is a diagnostic measurement that is used for identification of high degree metal tolerant organisms samples.

2.2.Pot experiment

The setup of this experiment was placed in ambient condition in Botanical Garden of GCU, Lahore. No extra instruments were utilized to regulate any abiotic factor such as temp, light and humidity. All 12 inch earthen pots were properly washed then dried and lined with polythene bag. Each pot was filled with 5.5kg soil mix with the 1:6 ratios of humus and garden soil respectively. Different concentrations of lead nitrate were added in the soil. Seven lead treatments named as To, T1, T2, T3, T4, T5, T6 were prepared have 0, 100, 200, 400, 600, 800 and 1,000mg of lead/kg respectively. The position of pot was consistently altered on a weekly basis to keep uniform climatic condition. All

All lead treatments comprised of constant agronomic practices. The measurement of all parameters was carried out at the time of harvest. All plants were properly rinsed after the harvesting. Later they were dried and polythene zipper bags were used to store them. Measuring rod & electric balance were used to measure the length, fresh biomass and dry biomass of root, shoot. The estimation of dry weight were carried out by drying the samples of crop were at 70°C temperature for a whole day. The attributes of yield were determined by the Zadoks protocols.

2.3.Biochemical and Physiological attributes

For the measurement of stomatal conductance, rate of photosynthesis and transpiration LCA4 Model Infra-Red Gas Analyzer was used. Leaves of tree were selected from each pot. At every 75th and 130th day readings were noted. Arnon protocols were followed to measure the contents of chlorophyll. Carotenoid was extracted in dim light in which one gram of fresh leaves were chosen arbitrarily and then crushed in (CH₃)₂CO. Then filtration of homogenate was carried out and the final volume was raised upto 50ml by adding more (CH₃)₂CO. Spectrophotometer was used for the estimation of carotenoids at the 440.5 nm wavelength.

“Carotenoids contents = [V × 383 × (As − Ab)] / (100 × W)”

Where: "V" is volume utilized for investigation; “383” is carotenoids extinction coefficient; “As” is sample absorbance; “Ab” is error in cuvette; “W” is sample weight in grams.

2.4. Mineral contents and quality attributes

Flame photometer was used to estimate Potassium. The quantification of phosphorous was carried out by drying one gram of sample of plant that later crushed. Then sample was placed in the furnace at 650°C temperature for three hours. These burned samples were later mixed in 10ml of 0.7 N sulphuric acid that stayed for one hour and later filtered through filter paper named Whatman No. 42 and the final volume was raised upto 50ml. For the preparation of stoke solution 0.43g of oven dried potassium phosphate (K₃PO₄) was mixed in 1liter of water. Then using this stock solution a number of standards ranging from 2ppm-50ppm were made. Ten milliliter of Ammonium vanadomo lybdate was mixed in crossponding 5ml standard and stayed for ten minutes then at the wavelength of 410nm absorbance was noted by spectrophotometer. Similar protocol was utilized for samples. The absorbance value of phosphorous and the absorbance value of the standard was used to plot the standard graph. Kjeldahl method and the following formula were used for the determination of Nitrogen:

Percentage of contents of Nitrogen = (A − B) × Normality of acid × 14.01 × 10 × 100/ Volume of sample

Where ‘A’ is used hydrochloric acid, B is hydrochloric acid utilized for blank; 14.01 is N atomic mass. whereas, the estimation of protein was carried out by multiplying 6.25 with percentage of nitrogen contents.

2.5. Accumulation of Lead

Chandra protocol is followed for the determination of lead accumulation in plants shoots, roots & leaves. The sample of crop was firstly rinsed with double distilled water then with 10mm solution of CaCl₂. Later dried and at 450°C samples were turned into ashes. Then 2% nitric acid is used for the digestion of ashes. After digestion of ashes it was filtered by using glass fiber filter.

Treatments	Dry weight of Seedling in grams	Fresh weight of Seedling in grams	Percentage Germination	Tolerance index	Seedling vigor Index
To	0.064±0.006 a	0.125±0.013 a	100±0.01 a	99.99±3.45 a	2916.67±100.66 a
T1	0.052±0.010 b	0.111±0.012 a	100±0.01 a	76.33±1.43 b	2226.67±41.63 b
T2	0.043±0.002 c	0.084±0.006 b	98±0.01 b	57.14±1.93 c	1638.87±39.40 c
T3	0.030±0.002 d	0.062±0.016 c	96±0.01 c	47.59±2.59 d	1272.40±73.74 d
T4	0.024±0.003 de	0.025±0.010 c	87±0.01 d	35.08±2.79 e	893.87±73.60 e
T5	0.021±0.002 de	0.043±0.003 cd	80±0.01 e	23.43±1.10 f	546.67±25.72 f
T6	0.017±0.001 e	0.033±0.006 d	70±0.01 f	15.08±1.91 g	308.00±38.97 g
F ratio	38.9816	35.0304	1.0868	539.2539	693.2351
LSD	0.0085	1.01698	343.9316	3.9219	107.5930

Table 1: Impact of Lead on parameters of wheat germination

Inductively coupled plasma spectrophotometer was used for quantification of lead (Pb). The limit of detection ranges from 8-80ng/L.

Figure 1: Toxicity of Lead (Pb) during germination of wheat

Data analysis:

ANOVA test and Duncan Multiple Range Test (DMRT) were used for the evaluation of Results.

3. RESULTS AND DISCUSSION

The present study shown several important outcomes concerning to the toxicity of lead in the wheat germination, biochemical, physiological, growth and attributes of yield. Information related to the features of germination shown that lead treatments had severely affected the percentage of germination, length of plumule, dry weight of crop, length of radical, fresh weight of the wheat and length of seedling as depicted in Fig. 1 & Table 1. The gradual Intensification of lead leads towards detrimental effects in wheat crop. In germination highest decrease was noted for example thirty percent. In comparison to the control in T6 (1000mg lead/L) the length of radical, seedlings fresh weight, seedlings dry weight, seedling vigor index & tolerance index was reduced by 45%, 74%, 77%, 89% and 74% respectively as depicted in Figure 1 & Table 1 also. It was observed by the Chun that during the process of germination at 0mg Pb/kg to 0.5 mg lead/kilogram concentration there is insignificant harmful effect of lead on index of germination and required energy. Likewise, at low concentration of lead contamination there is non-significant impact of lead contamination on rate of growth of shoots & roots (Alghobar and Suresha, 2017). But the concentration of lead above 4.5mg/kg in soil is harmful for the plant because it leads to reduction in germination (Yourtchi and Bayat, 2013). Lead toxicity majorly affects the roots of plants in comparison to other parts of plant (Barberon and Geldner, 2014).

Excessive contamination of lead caused the reactive oxygen species (ROS) formation in chloroplast, mitochondria & cellular compartments (Shahid, et al., 2014). The results obtained from this study about growth of seedlings corroborates with the study conducted by Yadav who stated that with increasing concentration of lead the attributes of growth were significantly affected (Yadav, et al., 2018).

Treatments	Root length (cm)	Plant height (cm)	Number of leaves	Fresh weight (g)		Dry weight (g)
Treatments	Root length (cm)	Plant height (cm)	Number of leaves	Root	Shoot	Root	Shoot
T₀	25.0 ± 0.15 a	68.7 ± 0.25	26.33 ± 0.58	1.26 ± 0.05	7.02 ± 0.09	0.92 ± 0.04	5.62 ± 0.01
T1	22.5 ± 0.26	66.1 ± 0.29	25.67 ± 0.57	1.19 ± 0.03	5.77 ± 0.04	0.83 ± 0.04	4.45 ± 0.06
T₂	20.9 ± 0.25	64.7 ± 0.38	23.99 ± 0.16	1.10 ± 0.09	5.09 ± 0.08	0.72 ± 0.05	3.79 ± 0.09
T₃	18.1 ± 0.38	62.0 ± 0.23	24.43 ± 0.23	0.95 ± 0.03	4.18 ± 0.07	0.63 ± 0.04	3.25 ± 0.02
T₄	16.0 ± 0.52	61.2 ± 0.31	22.97 ± 0.20	0.86 ± 0.01	3.85 ± 0.05	0.52 ± 0.06	2.89 ± 0.03
T₅	14.7 ± 0.26	60.2 ± 0.25	22.03 ± 0.04	0.76 ± 0.02	3.59 ± 0.06	0.40 ± 0.02	2.38 ± 0.07
T₆	13.5 ± 0.24	58.2 ± 0.32	20.96 ± 0.07	0.62 ± 0.04	2.53 ± 0.04	0.34 ± 0.05	1.61 ± 0.02
F-ratio	561.35	437.63	31.05	59.59	1596.57	76.79	2052.58
LSD	0.5479	0.5295	0.8978	0.0872	0.1140	0.07463	0.0899

Table 2: Effect of different Lead concentrations on growth attributes of wheat

Treatments	Rate of Transpiration (mmol m⁻²s⁻¹)	rate of Photosynthetic (µmolCO₂)	Stomatal conductance (mmolH₂O/m²s)
T₀	0.99 ± 0.020	8.088 ± 0.162	0.398 ± 0.008
T₁	0.734 ± 0.016	7.087 ± 0.156	0.289 ± 0.006
T₂	0.689 ± 0.013	6.787 ± 0.129	0.281 ± 0.005
T₃	0.654 ± 0.014	5.987 ± 0.132	0.141 ± 0.003
T₄	0.572 ± 0.011	4.203 ± 0.084	0.127 ± 0.003
T₅	0.352 ± 0.006	3.502 ± 0.063	0.093 ± 0.002
T₆	0.263 ± 0.004	2.115 ± 0.036	0.069 ± 0.0001
F-ratio	1,830.3037	4,962.6695	1,338.3403
LSD	0.0173	0.09328	0.0110

Table 3: Effect of lead toxicity on wheat’s physiological attributes

The co-cropping of soybean and T. minuta has increased the accumulation of lead in the later crops but no impact on health was caused by the consumption of grains of soybean (Vergara, et al., 2020). Data related to the attributes of growth revealed that the concentration of lead ranging from 0.01 to 0.05 significantly impact the growth of crop as depicted in Table 2 also. In T6 length of root (13.5±0.24 cm), the height of plant (58.2±0.32 cm) and leaves a number (21.67±0.05) were noticed minimum. At higher concentration of lead both fresh & dry weight was significantly reduced. In T6 fresh weight of shoot (2.53 ± 0.04), roots (0.66 ± 0.05) and dry weight of shoot (0.34±0.04), roots (1.61 ± 0.02) were also noticed minimum and also depicted in Table 2.

Gopal & Rizvi study also corroborates with this observation that with the increase in lead concentration decreases the weight and length of shoot and root. The detrimental effects of lead were not apparent in the life of plants at their early stage but as the level of maturity of the plant increases its adverse effects also increased (Gopal & Rizvi, 2008). The uptake of metal, bioaccumulation and translocation is proportional to the age attribute. It is also reported by Antoniadis study that when lead was present in an excessive amount the development of root was poor (Antoniadis, et al., 2017). The key reason behind the decrease in plant biomass is the reduced photosynthetic rate and metabolism of nitrogen (Hamid, et al., 2010). It was reported that the fresh weight of brassica was significantly affected by lead (Pb) concentration (Osma, et al., 2012).

Figure 2: Effect of concentrations of lead on wheat’s biochemical attributes

Treatments	Contents Of Potassium	Phosphorous contents (ppm)	Protein contents (%)	Nitrogen contents (%)
T₀	409.20 ± 0.10 a	18.87 ± 0.08	9.63 ± 0.06	1.54 ± 0.01
T1	350.37 ± 0.15 b	16.85 ± 0.08	7.90 ± 0.08	1.24 ± 0.02
T₂	349.60 ± 0.30 c	15.10 ± 0.22	5.68 ± 0.10	0.90 ± 0.01
T₃	339.33 ± 0.21 d	12. 86 ± 0.15	5.01 ± 0.01	0.79 ± 0.01
T₄	311.96 ± 0.12 e	10. 09 ± 0.06	3.44 ± 0.09	0.60 ± 0.00
T₅	291.33 ± 0.21 f	8.51 ± 0.12	2.55 ± 0.09	0.39 ± 0.02
T₆	269.57 ± 0.31 g	7.39 ± 0.14	1.75 ± 0.01	0.26 ± 0.02
F-ratio	139,098.1018	2,947.2309	4,585.5065	3,851.3114
LSD	0.3729	0.2395	0.1283	0.0224

Table 4: Effect of different Pb concentrations on wheat’s quality attributes and mineral content

The results of this study corroborate with the Zeng study who applied lead acetate at 6 different levels i.e. 0 to 900 mg/kg in his experimental analysis. This might be expected that lead poses a non-harmful effect at low concentration. With the increase in the concentration of lead, all biochemical & physiological features of the wheat crop were decreased that might be because of the toxicity of lead as it decreases the synthesis of chlorophyll, damages the structure of chloroplast, reduces the activities of carotenoids and restricted activities of enzymes. Lead toxicity also causes carbon dioxide deficiency (due to stomatal closure), obstructions in ETC (electron transport chain) and alternation in the thylakoid membrane (Zeng et al., 2006). It was reported that the presence of metal decreases the chlorophyllase that leads to low content of chlorophyll. And it was revealed by the studies that contents of chlorophyll a are less disturbed than chlorophyll b contents. Rafaqat in their research observed that elevated chromium stress decreases the Brassica napus L photosynthesis rate (Gill, et al., 2017).

The quality and minerals content attributes of wheat decreased significantly by all lead treatments (p≤0.01; 0.05) (Table 4). In T6 the content of Phosphorous, nitrogen, potassium and protein decreased from 11 to 58%, 38 to 82%, 14 to 34% and 18 to 81% respectively in comparison to the control. The attributes of yield were ranges as follows, K contents (409.20–269.57 ppm), contents of P (17.75–6.79 ppm), contents of protein (9.63–1.75%) and N contents (1.54–0.28%). The lead treatment significantly changed the results of the Pot experiment (Table 5). Yield decreases at higher concentrations. In T6 minimum weight of seed/plant (0.85 ± 0.09 g), seeds number/plant (16.33 ± 0.58), harvest index (263.39±11.52%), the weight of straw /plant (2.62±0.12 g) and weight of 1000 seeds (29.99±0.74 g) was noticed (Table 5). The attributes of all yields were decreased by the increasing concentrations of lead so to meet the growing feed requirement of the population farmers are intended to grow such crop varieties that produce more yields.

Treatments	Seed weight/plant (g)	Number of seed/plant	Straw weight/plant (g)	1,000 seed weight (g)	Harvest index (%)
T₀	7.57 ± 1.10 a	158.68 ± 28.04 a	6.98 ± 0.13 a	54.60 ± 0.79 a	700.29 ± 12.99 a
T1	4.54 ± 1.22 b	84.33 ± 18.01 a	5.13 ± 0.08 b	46.39 ± 0.48 b	515.41 ± 8.04 b
T₂	3.01 ± 1.07 c	55.67 ± 19.86 ab	4.48 ± 0.05 c	43.63 ± 0.33 c	449.56 ± 5.50 c
T₃	2.28 ± 0.98 cd	37.00 ± 16.52 b	4.07 ± 0.06 d	42.79 ± 0.14 c	408.39 ± 6.10 d
T₄	1.49 ± 0.06 cd	21.00 ± 1.00 b	3.69 ± 0.15 e	41.48 ± 0.19 d	370.65 ± 14.94 e
T₅	1.34 ± 0.03 d	19.00 ± 1.00 b	3.32 ± 0.08 f	39.11 ± 0.79 e	333.84 ± 8.63 f
T₆	0.85 ± 0.09 d	16.33 ± 0.58 b	2.62 ± 0.12 g	30.03 ± 0.63 f	263.48 ± 10.61
F-ratio	24.2617	3.3286	577.7730	557.7549	684.2652
LSD	1.4529	104.6137	0.17924	0.9465	39.2345

Table 5: Effect of various concentrations of lead on yield attributes of wheat

Treatments	Concentration of Pb in roots (μg/g)	Concentration of Pb in shoots (μg/g)	Concentration of Pb in seeds (μg/g)
T₀	4.7 ± 0.05	0.9 ± 0.09	0.194 ± 0.01 a
T₁	39.3 ± 0.03	15.6 ± 0.04	0.213 ± 0.06 b
T₂	53.9 ± 0.08	22.4 ± 0.08	0.271 ± 0.09 c
T₃	79.2 ± 0.04	37.3 ± 0.07	0.304 ± 0.02 d
T₄	94.6 ± 0.02	49.1 ± 0.05	0.356 ± 0.03 e
T₅	180.3 ± 0.05	60.7 ± 0.06	0.383 ± 0.07 f
T₆	221.2 ± 0.02	87.3 ± 0.04	0.422 ± 0.02 g
F-ratio	24.2617	259,169.857 1	22,153.4285
LSD	1.4529	0.17512	0.00175

Table 6: Accumulation of lead in roots, shoots and seeds of the wheat plant

The current focus of scientists is to develop more yield producing improved and new crop varieties with the help of genetic engineering. The present research investigates the detrimental impacts of lead on the yield of wheat crops. It is reported in a study by Xiong that vegetable crops such as spinach and cabbage which were grown near smelter contain concentrations of heavy metals such as Pb, Zn and Cd in them. Lead restricts enzymatic activities by interfering with the enzyme’s active sites that results in low yield (Xiong, et al., 2014). It is reported in a study that the yield of corn mint affected by 16% from a 400m away lead source through the air. Similarly, it was observed that air pollution is responsible for the reduction in essential oils yield by 14%. Gill et al. stated that chromium toxicity in cultivars of oilseed rape caused an increase in the number and size of grains of starch (Gill, et al., 2014).

Elite molecular transporters genes were revealed by the presence of heavy metals. MTs tend to perform the activity of transmembrane transportation of water (Gill, et al., 2017). The depictions of outcomes by the accumulation of lead in parts of wheat crop such as shoot, root & seed was shown in Table no. 6. The drastic alternations in the treatment means were also revealed. In comparison to control treatments, the degree of increase in the amount of lead was relatively alarming. For example, in T6 roots, seeds and shoots showed 4600%, 118% and 9800% increase in the quantity of lead respectively. The concentration of Pb declines majorly in roots then shoot and then in seeds of the wheat plant. In comparison to control the concentration of lead was significantly increased in T6 as depicted in Table 6 also. The amount of lead is directly related to the uptake of lead by roots. Different variables which contribute towards the adsorption of lead are microbial activity, fertilizer type, pH of the soil, extractable lead concentration in soil, fertilizer amount, precipitates of phosphate and carbonate (Gupta, et al., 2019). It was reported by Antoniadis that translocation of lead was significantly decreased by the movement of metal towards aerial parts, which indicated that accumulation of Pb was more in roots than shoots and seeds (Antoniadis, et al., 2017). Several studies revealed that there was a high amount of lead accumulation in roots such as Kenaf root tend to retain up to 85% of total lead, Tlaspi praecox up to 80% of total lead and Brassica junce tends to hold up to 95% of total lead.

It is concluded by Zhang that cultivars of rice have several factors for translocation and uptake of metal. Translocation and absorption of lead to leaves of plants rely upon different factors that vary from one crop to another crop (Zhang, et al., 2010). Accumulators in shoots tend to store more lead in plant shoots while accumulators in roots tend to hold more lead in plants roots and permit transportation of only a minute concentrations of Pb to aerial crop parts. Similarly, it is revealed in another study that the surface area of roots determines the uptake of Pb by plants (Shahid, et al., 2016). Heavy metal significantly impacts the tip cells of the root as disruption of the cell membrane, enlarged vacuole, injuries in thylakoid of mitochondria and plasmolysis was most noticeable in cells of root (Gill, et al., 2014). The difference in the rate of translocation was caused by the existence of significant lead concentration in plants. It was concluded by Sharma that lower molecular complexes and ions are more moveable forms than other forms. Roots might accumulate more concentration of (Pb) lead in such plants but high molecular complexes & weight constrain distribution & translocation of lead to above-ground parts of the crop. Basharat et al. conducted an experimental analysis and observed that lead is responsible for the decrease in. macronutrients concentration in shoot, decline in biomass, increase in MDA & reactive oxygen species (Khan, et al., 2013). It is revealed in a study that the application of plant growth regulators can counter the detrimental impacts of such heavy metals in wheat and other crops (Ali, et al., 2015).

4. CONCLUSION:

This study revealed that lead causes several adverse impacts on wheat yield, germination, biochemical, physiological, mineral, growth and quality feature. Results revealed that all negative effects of Pb (lead) were mainly caused by a reduced rate of photosynthesis and associated phenomena such as reduced conductance of stomata and reduced rate of transpiration. It was also observed that the rate of accumulation of lead in parts of wheat crop such as seeds, shoots & roots was above the permissible/threshold level. In Pakistan wheat is an essential food therefore the contamination of Pb in wheat is alarming. The gradual accumulation of lead (Pb) eventually causes serious illness & disorders. So certain remedial practices ought to be taken on to limit the entry of lead into wheat from contaminated soils. So, currently, it is the need of an hour to maintain the supply of lead-free wheat.

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Laureate Folks

Investigation of industrial wastewater effects on wheat yield, growth, nutrients germination and lead bio-accumulation