Research Article - International Research Journal of Plant Science ( 2020) Volume 11, Issue 1
Received: 12-Apr-2020 Published: 08-Jun-2020, DOI: 10.14303/irjps.2020.003
Nickel is well thought-out to be an indispensable micronutrient for plants, however at excess concentration, it proves toxic to the plants and toxicity of this metal has been attributed to its negative effect on various physiological and biochemical parameters as photosynthesis, mineral nutrition, sugar transport and plant water relationship. In this study, it was assessed that different concentrations of nickel appreciably effect the levels of soluble sugar, proline and glycinebetaine along phosphorus metabolism in two cultivars of wheat (UP2382 and VL616) but the cultivar VL616 was found to be more responsive to nickel stress. The present study encompassed two experimental lines simultaneously involving nickel treatment viz. 50μM (T1), 100μM (T2) and 150μM (T3) in both cultivars (UP2382 and VL616). The results of the study indicated highly significant (p < 0.001) changes in the biological parameters evaluated in nickel treated wheat plants as compared to their controls. The study proposed that the Cultivar VL616 was more responsive to nickel stress as evidenced by the higher accumulation of sugar, glycinebetaine and proline contents and exhibited minimum decrease in the phosphate levels during the course of nickel treatments than UP2382 cultivar. There might be increase in Salicylic acid and Abcessic acid levels in cultivar UP2382 than in cultivar VL616 that makes the cultivar UP2382 less susceptible to nickel stress. Thus, Nickel stress leads to change in various biological parameters in wheat plants and by increasing the concentration of this micronutrient, there is variable changes in these parameters. However, plants combat abiotic stress factors by regulating the levels of these biological parameters.
Nickel, among one of the important metal pollutants on earth is of significant concern, because its concentration is rapidly escalating in soils of different parts of the world (Faryal et al., 2007; Atiq-ur-Rehman & Iqbal, 2008). Nickel forms an essential micronutrient for plant growth and it is also a component of the enzyme urease which is required for nitrogen metabolism in higher plants. For normal metabolic functioning in plants, micronutrients play an essential role but at higher concentration they are toxic to plants. The concentration of nickel in the environment is consequently elevated by emissions of nickel from the variety of natural and anthropogenic processes. Increase in concentration of Nickel through natural process includes weathering of minerals and rocks, whereas different compounds of nickel (such as nickel acetate, nickel carbonate, nickel hydroxide and nickel oxide) are used in a variety of industrial process makes up rise of this micronutrient and leads to toxicity (Cempel & Nikel, 2006). These compounds ultimately accumulate in the soil and environment, and can be easily taken up by plants. Thus, they can enter in the food chain and cause deleterious effects on animals and human lives (Cempel & Nikel, 2006). Plant growth and metabolism are greatly influenced by nickel concentrations. At lower concentration of nickel, it proves beneficial for growth and development of plants, but at higher concentrations, it showed deleterious effects on plants (Kochian, 1991; Welch, 1995; Hasinur et al., 2005). Ni is present in hydrated form in the soil solution Ni (H2O)26+ (Yusuf et al., 2011). Although, the toxic effects of excess nickel are evident through crop development, the germination stage is regarded as the most sensitive particularly to nickel. Increasing concentration of this micronutrient inhibits seed germination and seedling growth of different plant species (Farooqi et al., 2009). The Ni-induced growth inhibition has been attributed to down-regulation of protein synthesis and activities of some key enzymes responsible for mobilization of food reserves during seed germination (Bishnoi et al., 1993). In addition to this, Ni is a well-known active competitor of a number of indispensable micro- and macro-elements and is supposed to reduce the uptake of elements in germinating seeds, resulting thereby in poor germination and seedling establishment (Korner et al., 1987; Kochian, 1991). In order to overcome the negative effects of high nickel concentrations in plants, addition of supplement Ca2+ could be used to overcome the negative effect.
Wheat is an important cultivable crop after Rice throughout the world. The current study was conducted to evaluate the effect of different concentrations of Nickel on different parameters in two cultivars of wheat. In this scenario, it was found that higher concentration of this micronutrient makes reasonable changes in phosphorus content and other parameters in both cultivars. However, Cultivar UP2382 showed more resistance to the Nickel stress than cultivar VL616.
Authenticated seeds of two genotypes (UP2382 and VL616) of Triticum aestivum were taken from the Genetics Division, IARI, New Delhi, India. After thorough washing of seeds with water, seeds were surface sterilized with 0.01 % mercuric chloride. The seeds were washed again with distilled water and were sown in the pots containing the mixture of sand and vermiculite (1:1). After germination, three plants were maintained in each pot (Hummert International, Earth City, MO, USA) and plants were grown in Hoagland solution (Hoagland & Arnon 1950) of one-fourth strength for first 10 days. For next ten days in half-strength of Hoagland solution and in full strength for the last ten days. The plants were grown in the growth chamber under the controlled conditions of light (16h photoperiod), temperature (270C) and humidity (60%). Following treatments were given to 30 days old plants, T0 = 0 μM Ni, T1 = 50 μM Ni, T2 = 100 μM Ni, T3 = 150 μM Ni. The treated genotypes were taken in triplicates along with the control of each genotype during sampling. 48 plants of each variety were grouped into 4 groups, each group including 3 plants of each variety. Leaves of 30 days old plants were excised and used for experimental examination. The whole experimental procedure involves the utilization of three biological replicates.
Estimation of proline content
Proline content was determined by following the method of (Bates et al., 1973). 0.5 g of leaf sample was homogenized in 3% sulphosalicylic acid (10ml) followed by centrifugation at 10,000 rpm for 10 minutes. The supernatant (2ml) was taken in test tube and 2 ml of acid ninhydrin along with 2 ml of glacial acetic acid were added. The mixture was incubated at 100 ˚C in a water bath for one hour and the tubes were placed in an ice bath to terminate the reaction. 4ml of toluene was added to each tube and mixed vigorously on a vortex for 10-30 seconds. The supernatant layer was taken from the mixture and absorbance measured at 520 nm using toluene as blank. The concentration of proline in samples was calculated against the standard curve of proline, expressed in μg g−1 fresh wt.
Soluble sugar content of leaves
Soluble sugar content was estimated by employing phenolsulphuric acid method of (Dubois et al., 1956), Briefly, 0.5g of leaf samples were extracted by adding 80% (v/v) methanol keeping the solution at 70°C in a water bath. The resulting extract was centrifuged at 5,000 × g for 10 min at 4°C. The supernatant was collected and treated with 5% phenol and 98% sulphuric acid. The reaction mixture kept for 1h and then absorbance was measured at 485 nm. Soluble sugar content was calculated in mMg−1FW.
Estimation of glycine betaine content
Glycine betaine content was determined following the procedure of (Grieve & Grattan, 1983). In brief, 0.5 g of leaf material was homogenized with 20 ml mili-Q water for 48 h and filtered. The filtrate was diluted with equal volume of 1M H2SO4 kept in ice-cold water for 1h for cooling and then cold potassium iodide-iodine reagent was added to it. The mixture was gently vortexed, stored at 4 °C overnight and centrifuged at 12 000 x g for 15 min at 4 °C. The precipitated per iodide crystals were collected and dissolved in 1,2-dichloroethane, and the absorbance was measured at 365 nm after 2 h using glycinebetaine (dissolved in 1 M H2SO4) as the standard. Glycinebetaine content was calculated in μg g−1FW.
Estimation of phosphate content
Phosphate content was estimated by the method of (Ames, 1966). Briefly, 0.5g of leaf sample was taken in silica crucible. One ml of 10% Mg (NO3).6H2O (in 95% ethanol) was added to it before powdering it to ashes in a muffle furnace at 600˚C for four hours. Reaction mixture (2.3ml) containing 10% ascorbic acid and 0.42% (NH4)6MO7O24.4H2O (made in 0.5M H2SO4) in 1:6 ratio and the solution was kept for 10 min at 45˚C to complete the reaction. The absorbance was measured at 820 nm and phosphorus content was calculated from the standard curve prepared using analytical-grade KH2PO4.Phosphate content was determined in μg g−1FW.
Statistical analysis
We carried out the statistical analysis by using one-way ANOVA using Duncan’s multiple range test (SPSS17.0); The results were compared for significance at p< 0.05 and the results were presented as mean ± SD (n = 3).
The results that were obtained in this study indicated that nickel toxicity in plants leads to an inhibition of growth, chlorotic, necrotic and wilting processes. Toxicity of this metal has been attributed to its negative effect on photosynthesis, mineral nutrition, sugar transport and water relations. Ni at different concentrations considerably influences the biochemical reactions of plants, including phosphorus metabolism and glycinebetaine and proline contents. In response to stress, plants show variable changes in these biochemical parameters. In this study, two strains of wheat showing different responses on nickel amendments of variable concentrations and the results determined that VL616 variety is greatly influenced by the stress levels as there is maximum change in these biochemical parameters as compared to UP2382 variety. These variable findings in results might be due to the presence of high content of flavonoids, phytoalexins, phenolic compounds and increase in defense signaling pathways in cultivar UP2382 than in VL616 to combat the stress as due to increasing stress levels of the heavy metals, UP2382 is found to be resistant than VL616.
The study indicated that nickel is considered to be an essential micronutrient for plants, however at excess concentrations this metal becomes toxic for majority of plant species. This study will help the researchers to use the micronutrients in a proper way and higher applications of this micronutrient will prove fatal for the plant growth and will lead to abiotic stress to plants.
The author would like to thank gratefully the department of Botany, Jamia Hamdard University for providing all laboratory facilities in completing this work.
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