An Overview of Nickel Toxicity in Plants

Mohsin Tanveer

University of Tasmania

CONTENTS

28.1 Introduction..........................................................................................................................465

Essentiality of Ni and Its Role in Plant Growth and Development

  • 28.3 Plant Responses under Ni Toxicity.......................................................................................467
  • 28.3.1 Plant Growth and Development................................................................................467
  • 28.4 Photosynthesis and Photosynthetic Pigments.......................................................................468
  • 28.5 Membrane Permeability and ROS Production.....................................................................469
  • 28.6 Conclusion............................................................................................................................470

References......................................................................................................................................470

Introduction

Nickel (Ni) is the most abundant element after iron on the earth’s crust and comprises roughly 0.008% of total earth crust (Hedfi et al. 2007; Hussain et al. 2013). Approximately 10% of Ni in earth crust is being locked up in molten Fe-Ni ore (Ahmad et al. 2011). Worldwide, Ni is present in different soils ranging from 20 mg/kg in China to 420 mg/kg in the USA (Figure 28.1). Ni is a transition metal element and is widely accepted as an essential element for plants (Matraszek et al. 2016). Nonetheless excess concentration of Ni in our environment makes it a toxic element and thus release of Ni into the environment is of great concern that includes a deposition in agricultural soils (Jamil et al. 2014). Generally, optimum or sub-lethal Ni concentration should be lower than 100 ppm in soil and 0.05 ppm in surface water; however, inevitable anthropogenic activities and unnecessary industrial developments are increasing Ni concentration in soil and water (Shahzad et al. 2018). Ni is being added in our environment via different means such as smelting, burning of fossil fuels, mining, disposal of industrial waste, and effluent from Ni-based metallurgy and electroplating industry (Orlov et al. 2002). Therefore it is important to understand the role of Ni in plants. In this chapter, the essential role of Ni in plant metabolism has been discussed and Ni toxicity in plants has also been overviewed.

Nickel concentration (mg/kg) in the soil around the globe (Chen et al. 1999)

Figure 28.1 Nickel concentration (mg/kg) in the soil around the globe (Chen et al. 1999).

28.2 ESSENTIALITY OF Nl AND ITS ROLE IN PLANT GROWTH AND DEVELOPMENT

An element is considered as an essential nutrient when the plant cannot perform its normal life cycle without that element. Ni was considered as toxic element ages ago, however, during 1987, Mr. Brown and his co-workers established that Ni is an essential nutrient; however, its essentiality largely depends on its concentration in the growth medium. Generally, optimal Ni concentration ranges from 0.05 to 10 mg/kg in plant tissues (Nieminen et al. 2007). Later on, researchers around the globe discovered the positive and essential role of Ni in plants. Ni has been found as a prime component of numerous enzymes, as it develops bonds with S-ligands and O-ligands (Marschner 2002). Moreover, urease is the only enzyme in plant which requires Ni as its essential component (Ojeda-Barrios et al. 2016). Urease activity is highly sensitive to Ni deficiency; even a minute change in optimal Ni concentration reduces urease activity up to 25%, which concomitantly disrupts N metabolism in plants (de Queiroz Barcelos et al. 2017; Hussain et al. 2020).

The essentiality of Ni in plants can also be observed from previous findings such as Ni deficiency results in leaf injury, necrosis, stunted root growth and nodule development in legumes, and reduced iron uptake (Chen et al. 2009; Zobiole et al. 2010; Shahzad et al. 2018). Nonetheless, the application of Ni in low concentration alleviates these symptoms and improves plant growth and is also required for hydrogenase enzyme, an important enzyme required to reduce nitrogen into ammonia (Dalton et al. 1985), and Ni deficiency significantly reduces hydrogenase activity (Ahmad and Ashraf 2012). Ni deficiency also disrupts N metabolism in plants by disturbing amino acid metabolism especially cysteine amino acid, polyamines biosynthesis pathway, and ornithine cycle intermediates (Bai et al.

2006; Sachan and Lai 2017). Moreover Ni deficiency also interferes with the TCA cycle by reducing the citrate level in plants (Bai et al. 2006). Furthermore, due to the fact that Ni plays a prime role in the activities of several enzymes, it is shown to be an important promoter of plant growth and development at low concentrations (Gajewska & Sklodowska 2005, Shahzad et al. 2018; Daneshmand et al. 2019). Ni improves disease resistance in plants by triggering disease resistance mechanism and by exerting direct antagonistic effects on pathogens (Brown 2007).

Ni at low concentration increases overall plant biomass production by improving plant growth, leaf area development, root proliferation, carbon assimilation process, and water retention in plants (Seregin and Kozhevnikova 2006; Prasad and Shivay 2019). The application of Ni at the concentration of 10 pM improved the fresh and dry weight of wheat seedlings as compared with control plants grown without Ni (Gajewska et al. 2006). Likewise, Ni improved seedling length, number of branches, and biomass accumulation in Hibiscus sabdariffa seedlings (Aziz et al. 2007). As mentioned above, Ni is important for urease enzyme activity, thus the presence of an adequate amount of Ni in xylem sap is important for the RNAase activity and nutrient uptake (Bai et al. 2013). Moreover several reports indicated that Ni-induced growth improvement was due to the direct and essential role of Ni in N metabolism (Gheibi et al. 2009; Khoshgoftarmanesh et al. 2011; Kutman et al. 2013,2014; Alibakhshi and Khoshgoftarmanesh 2015). Ni at low concentration improves nitrogen reductase enzyme activity in different plant species (Gad et al. 2007; Tabatabaei 2009). Ni is also an essential component of hydrogenase (Ni-Fe) that takes part in the recycling of H2, an obligatory product of N2 reduction (Gonzalez-Guerrero et al. 2014). Pre-treatment with Ni improved urease activity and higher N contents in grain, which was positvely correlated with increased N-remobilization or from older to younger leaves (Kutman et al. 2013, 2014; de Macedo et al. 2016). In short, Ni at low concentration is important for plant growth and development.

 
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