Elsevier

Ecotoxicology and Environmental Safety

Volume 160, 30 September 2018, Pages 10-18
Ecotoxicology and Environmental Safety

Effect of Cd on growth, physiological response, Cd subcellular distribution and chemical forms of Koelreuteria paniculata

https://doi.org/10.1016/j.ecoenv.2018.05.026Get rights and content

Highlights

  • Koelreuteria paniculata is an efficient Cd excluder.

  • Fixation of cell wall and compartmentalization of vacuole play an important role in reducing the toxicity of Cd.

  • Cd is converted to a highly active form at high Cd stress.

  • Antioxidant enzyme system, hormone and AsA-GSH cycle effectively reduce Cd toxicity.

Abstract

Koelreuteria paniculata were cultivated in nutrient solution with different concentrations of Cd (0, 50, 150, 250 and 500 µM) and sampled after 90 days. The resistance, translocation, accumulation and stress responses in Koelreuteria paniculata were investigated by hydroponic experiments. The results showed that Koelreuteria paniculata is an efficient Cd excluder that can tolerate high concentrations of Cd (up to 150–250 µM of Cd). The concentration of Cd never exceeds 5 ppm in leaves and 10 ppm in roots. The high concentration of Cd (≥ 250 µM) had a toxic effect on K. paniculata and significantly restricted the plant growth. The accumulation ability of Cd by different plant tissues followed the sequence of roots > leaves > stems. The bioconcentration factors and translocation factors both were less than 1. Cd has the highest content in the cell wall and is migrated to soluble fractions and organelles at high concentrations. Undissolved Cd phosphate, pectates and protein-bound Cd were the predominant forms. The low concentration of Cd (≤150 µM) promoted the synthesis of soluble proteins, AsA and GSH, while high concentration of Cd clearly inhibited the physiological and biochemical process, caused membrane lipid peroxidation and severe membrane damages, and increased MDA and H2O2 contents. POD, CAT and SOD exhibited positive and effective responses to low concentration Cd stress, but could not remove the toxicity caused by high concentration Cd stress. The content of IAA, GA and ZT decreased and ABA content was significantly increased under high-concentration Cd stress.

Introduction

The heavy use of cadmium (Cd) containing fertilizers, and mining exploitations has led to a gradual concentrations of cadmium in the soil environment. Cd cannot be microbially degrade in soil, with the property of persistence and bioaccumulation (Azevedo et al., 2012, Dhir et al., 2009, Xin et al., 2013). Cd is not an essential element for biological growth. It is highly toxic and poses a threat to living organisms, from microorganisms to animals, affecting its normal growth and causing death (Dalcorso et al., 2010; Alessandro et al., 2012). For the heavy metal pollution in soil, phytoremediation is safe and reliable, with good economic and ecological benefits (Xue et al., 2014, He et al., 2014, Bjelková et al., 2011). In addition, phytoremediation can prevent soil erosion and water loss, improve the condition of landscape. On this foundation, phytoremediation is considered a sustainable way for the wide application in environment remediation of heavy metal contaminants (Cluis, 2004, Ghosh and Singh, 2005). Many herbaceous species including Typha latifoia, Thlaspi caerulescens, Arabidopsis halleri, Miscanthus floridulus (Labill) Warb, Eremochloa ciliaris L., Sedum alfredii H. and Solanum nigrum L. have been confirmed to be able to accumulate and transfer heavy metals such as Pb, Cd and Mn in mine areas. Herbaceous plants are widely used in the soil restoration of heavy metal contaminated areas. However, each species produces a low biomass. Additionally, shallow root systems for these plants limit the removal of heavy metal from deep soil (Keller et al., 2003). There are also some non-hyper-accumulator plants, such as willows, eucalypts, poplars, Brassica napus and sunflower (Iori et al., 2017, Guo et al., 2015, Ehsan et al., 2014), can be used for phytoremediation because they have large biomass, rapid growth and deep root system (He et al., 2013). However, these plants are generally less resistant to Cd, which limits their repair efficiency. Woody plants with great biomass and high tolerance to heavy metals may be an alternative. (Pulford and Watson, 2003, Mukhopadhyay and Maiti, 2010).

Koelreuteria paniculata is a deciduous species of the sapindaceae family native to China, Japan, and Korea. It can resist salinity, drought and short-term flooding. This species have a deep root system, and is strongly adaptable to the environment (Zhang et al., 2017). These characteristics make it a good tree species for phytoremediation in heavy metal contaminated areas. In 2004, a three-square-kilometer base with K. paniculata ecological restoration was established in Xiangtan Manganese Mine, Hunan, China. It is a successful case of using K. paniculata to repair waste mining area (Tian et al., 2009). It tentatively confirmed that K. paniculata is highly resistant to various heavy metals and has certain potential of phytoremediation for heavy metal contaminated soils. So far, the reports of K. paniculata mainly focus on biological characteristics, pharmacology and chemical composition (Huang et al., 2015, Luo et al., 2015, Pipinis et al., 2015, Mostafa et al., 2014). The mechanism of plant tolerance to Cd has been reported quite a lot, but relatively few reports on woody plants and even more rarely reported on K. paniculata. Koelreuteria paniculata is known to grow on metal contaminated sites and thus might be involved in phytoremediation process. But its response to metal exposure (notably Cd exposure) has never been described so far. So, the resistance, translocation, accumulation and stress responses of K. paniculata to different concentrations Cd has yet to be studied thoroughly. Therefore, the present research is intended to: (1) investigate the effects of Cd on the growth of K. paniculata; (2) explore the subcellular distribution and chemical forms of Cd in K. paniculata; (3) examine the effects of Cd on physiological and biochemical indexes of K. paniculata, including chlorophyll, malondialdehyde, soluble protein, hormone contents, and antioxidant enzymes in order to uncover the potential mechanisms with regard to the uptake, accumulation, translocation and tolerance of Cd in K. paniculata. The results of this study are expected to provide the theoretical basis for the application and improvement of phytostabilization of K. paniculata in heavy metal contaminated soil.

Section snippets

Plant cultivation

K. paniculata seedlings were obtained from Central South University of Forestry and Technology, Changsha, PR China. All seedlings were 1-year-old and of similar size: 50 cm high, with a diameter of 0.5 cm. They were grown in 20% Hoagland-Arnon nutrient solution and cut off all branches. The seedlings of K. paniculata were precultured for 4 weeks for the initiation of the new roots before they were exposed to Cd stress. Then they were used for pot experiment. Pot experiment was conducted by

Plant growth parameters

In order to determine the tolerance of K. paniculata to Cd, we measured the effect of Cd on growth parameters of K. paniculata. Plants can tolerate up to 150 µM added Cd with no obvious change in any growth parameter (P > 0.05) (Table 1). Root lengths decreased at 250 µM added Cd, relative to the plants unexposed to Cd (P < 0.05) (Table 1). The number of new branches generated at top and base nodes was higher in plants with 150 µM added Cd than those with 250 µM added Cd (p < 0.05) (Table 1).

Cd effect on growth

Cadmium is highly toxic to plants (Li et al., 2010). Some studies have reported that, Cd stress inhibits plant growth and biomass (Ali et al., 2014, Mostofa et al., 2015), and also affects plant uptake and translocation of essential nutrients by competition (Liu et al., 2003, Sun et al., 2012, Pereira et al., 2017). In our study, plants tolerated up to 150 µM added Cd with no obvious change in any growth parameter (p > 0.05) (Table 1). When the Cd concentrations was higher than 150 µM, this

Conclusions

The resistance, translocation, accumulation and stress responses of Koelreuteria paniculata are reported in this paper for the first time. Koelreuteria paniculata is an efficient Cd excluder that can tolerate high concentrations of Cd (up to 150–250 µM of Cd). Under low Cd concentrations stress (≤150 µM), fixation of cell wall and compartmentalization of vacuole appear to play an important role in reducing the toxicity of Cd. Antioxidant enzyme system, hormone and AsA-GSH cycle also play an

Acknowledgements

This work was supported by the Young Scientists Fund of the National Natural Science Foundation of China (21707169), the National Key Technology Research and Development Program of the Ministry of Science and Technology of China (2016YFD0800805-4), the Hunan Provincial Innovation Foundation for Postgraduate (CX2017B404), Innovation Foundation for Postgraduate of Central South University of Forestry and Technology (CX2017B13)

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