Effects of tetracycline on growth, oxidative stress response, and metabolite pattern of ryegrass

https://doi.org/10.1016/j.jhazmat.2019.120885Get rights and content

Highlights

  • The growth of ryegrass weakened as tetracycline concentration increased.

  • Tetracycline triggered strong oxidative stress.

  • 3 metabolic pathways were different under tetracycline in the roots.

  • 11 metabolites could have crucial functions to the extension of roots.

Abstract

Tetracycline is an antibiotic that frequently contaminates the environment. In this study, the growth and metabolites of ryegrass seedlings treated with tetracycline (0, 1, 10 or 100 mg/L) for 5 days were investigated. The results showed that the growth of ryegrass and the concentrations of carotenoid and chlorophyll decreased as the tetracycline concentration increased. Tetracycline increased the production of reactive oxygen species (ROS) and cell permeability and triggered mitochondrial membrane potential loss in the roots of ryegrass. The metabolic profiles of ryegrass differed between the control and tetracycline-treated groups. The contents of glucose, shikimic acid, aconitic acid, serine, lactose, phenylalanine, mannitol, galactose, gluconic acid, asparagine, and glucopyranose were positively correlated with root length and had high variable importance projection values. These compounds may have crucial functions in root extension. Tetracycline also affected aminoacyl-tRNA biosynthesis, nitrogen metabolism, and alanine, aspartate and glutamate metabolism in the roots. Tetracycline may affect root extension by regulating the synthesis/degradation of these metabolites or the activity of their biosynthetic pathways. These results provide an insight into the stress response of ryegrass to tetracycline.

Introduction

Human activities have led to pollution of the environment with organic and inorganic compounds (Zou et al., 2016; Jin et al., 2011). Antibiotics are widely used to control the growth of microorganisms to control diseases and infections. However, excessive use can lead to antibiotic resistance, resulting in a reduction in their effectiveness (Sherpa et al., 2015; Lv et al., 2017). Antibiotics have some side effects, and can negatively affect aspects of human growth and metabolism, for example, they can damage children's hearing (Zakordonets et al., 2016). Because of their widespread use, antibiotics have become one of the most important environmental pollutants (Peng et al., 2017; Cheng et al., 2016). Antibiotics pose serious threats to the growth and metabolism of plant. For example, the studies have shown that antibiotics can influence the growth and antioxidant enzyme activities of wheat (Xie et al., 2011).

Plants are basic and key biological components of the ecological system (Guo et al., 2014; Khodakovskaya et al., 2011). Seed germination is the initial stage in the plant life cycle, and germinating seeds are very sensitive to various internal and external stimulants (Yin et al., 2012). Seed growth, leaf pigment content, antioxidant enzyme activity and protein expression are common test indexes of phytotoxicity (Chandra et al., 2008; Alfiya and Dheera, 2015; Lahiani et al., 2013). Other indexes include certain metabolites that are directly involved in biochemical processes in the plant cell (Moussaieff et al., 2013), as they reflect the results of changes in gene expression (Ryan and Robards, 2006). In recent years, certain metabolites have been used as potential indicators in global analysis of biological effects (Moussaieff et al., 2013; Zhao et al., 2016; Szewczyk et al., 2015; Pidatala et al., 2016; Booth et al., 2015). Changes in the concentrations of metabolites detected in metabolic analysis can provide an overall understanding of the whole stress response (Moussaieff et al., 2013; Pidatala et al., 2016; Booth et al., 2015). This can reveal details of the comprehensive biological response, clarify the consequences of changes in the levels of certain compounds, and provide information on how plants respond to changes in their environment (Hu et al., 2016a).

In this study, we analyzed the growth and metabolites of ryegrass treated with tetracycline. The purposes of this study were as follows: (1) to evaluate potential impacts of tetracycline on the growth and development of ryegrass; and (2) to elucidate the biomolecular regulation of seedling growth by tetracycline using a metabolic analysis.

Section snippets

Material and methods

Ryegrass seeds were soaked in 2% H2O2 for 15 min and then washed with deionized water. Seeds were cultivated in culture dishes (9 cm diameter) on filter paper. The concentration range of tetracycline was 1 − 100 mg/L. In the control group, the tetracycline was replaced with deionized water. Petri dishes were kept under the following conditions for 5 days: 18–25 °C and 70% humidity, 16-h light (illuminance: 6000 lux) / 8-h dark photoperiod. The morphology indexes and pigment content were

Changes in pigment content and morphological indexes

The morphological features of shoots and roots of ryegrass treated with tetracycline were analyzed by light microscopy (Fig. 1). As shown in the images, the pigment content in leaves was higher in the control than that in the tetracycline-treated plants. The pigment content reduced as the tetracycline concentration increased. The contents of chlorophyll and carotenoid are shown in Fig. 2. The chlorophyll content was remarkably higher in the control than that in the other groups. Compared with

Conclusions

This study demonstrated that tetracycline affected ryegrass growth and metabolism. The tetracycline inhibited growth and biomass accumulation, reduced pigment content, increased ROS level, SOD activity, and MDA content, and reduced CAT activity. A metabolic analysis provided insights into the stress response of ryegrass to tetracycline. We analyzed the relationships between metabolites and root length, and identified metabolites showing changes in abundance under tetracycline treatment. Total

Acknowledgements

This work was supported by the National Natural Science Foundation of China [31700368], the National Key Technology R&D Program of China During the 13th Five-Year Plan Period [2016YFD0201000], the Natural Science Foundation of Henan Province [162300410110], the Key R&D and Promotion Project of Henan Province [182102110049, 192102110043, 192102110155], and the Basic Research Project of Natural Science in Henan Institute of Science and Technology [207010617002]. We thank Jennifer Smith, PhD, from

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