A Mechanistic Study on the Toxic Effect of Copper Oxide Nanoparticles in Soybean (Glycine max L.) Root Development and Lignification of Root Cells

Abstract

Copper oxide nanoparticles (CuONPs) are widely used in several products and their release into the environment can cause toxicity to major food crops. In this study, toxic responses as a result of CuONPs exposure were studied in soybean (Glycine max L.) seedlings. The plants were grown in 1/2 strength Murashige and Skoog medium containing 0, 50, 100, 200, 400, and 500 mg/L of CuONPs in a growth chamber at 26 ± 2 °C with 16/8 h light/dark photoperiod for 14 days. The toxic effects of CuONPs were tested on the shoot and root development, total chlorophyll content, hydrogen peroxide generation, peroxidase (POD) enzyme activity, and lignification of root cells. The mRNA expression of different genes involved in lignin biosynthesis viz. phenylalanine ammonia lyase (PAL), cinnamate 4-hydroxylase (C4H), cinnamyl alcohol dehydrogenase (CAD), peroxidase 2 (POD2), peroxidase 4 (POD4), and peroxidase 7 (POD7) was studied using real-time polymerase chain reaction. Exposure to 500 mg/L of CuONPs significantly reduced the shoot growth, weight, and total chlorophyll content. However, the root length and fresh weights were significantly reduced at all concentrations of CuONPs exposure. Exposure to 100, 200, 400, and 500 mg/L of CuONPs significantly increased the hydrogen peroxide level, POD activity, and lignin contents of roots. Treatment with 2,7-dichlorofluorescein diacetate indicated a concentration-dependent increase in reactive oxygen species generation in roots. Staining with phloroglucinol-HCl revealed a concentration dependant increase in lignification of root cells. The expression levels of PAL, C4H, and CAD genes were significantly up-regulated upon exposure to 100, 200, and 400 mg/L of CuONPs. Significant up-regulation in the expression levels of POD2 and POD4 genes was observed upon exposure to 100, 200, 400, and 500 mg/L of CuONPs. Exposure to 200, 400, and 500 mg/L of CuONPs resulted in significant up-regulation of POD7 gene. These results for the first time show that exposure to CuONPs causes enhanced lignification of root cells and thereby affect root development in soybean seedlings.

Modulation of CuO nanoparticles toxicity to green pea (Pisum sativum Fabaceae) by the phytohormone indole-3-acetic acid

“…To avoid aggregation, suspensions/solutions were sonicated for 30 min in a water bath at 25°C (Crest Ultrasonics, Trenton, NJ Model 275 DA; 120 V, 3 A, 59/60 Hz). Levels of CuO were selected after Nair and Chung (2014), with a reduced number of concentrations, due to the number of Cu compounds. Solutions of IAA (Aldrich Chemicals) were prepared at 0, 10, and 100 μM, as described by López et al (2007a).…”

“…In hydroponically grown lettuce (Lactuca sativa), nano-CuO at 20 mg/L reduced water content, root length and dry biomass (Trujillo-Reyes et al, 2014). In soybeans (Glycine max) nano-CuO reduced shoot growth, plant weight, and chlorophyll content (Nair and Chung, 2014), Additionally, Hong et al (2015) reported that nano-CuO reduced root length in hydroponically grown alfalfa (Medicago sativa) and lettuce.…”

Evaluation of the effectiveness of Safflower (Carthamus tinctorius) seeds amendment with silicon or humic acid during germination under CuO (NPs) phytotoxicity

“…Shi et al (2014) and Stampoulis et al (2009) reported that Cu nanoparticles reduced root length, compared to the control. Nair & Chung (2014) recorded drastic roots-growth retardation under 400-500mg L -1 CuO NPs in soybean. In previous experiment on the nano-CuO on Hordeum vulgare, a restriction in root and shoot growth with decreased photosynthetic performance index were recorded (Shaw et al, 2014).…”

Root Morphologycal Responses of Oil Palm (Elaeis guineensis Jacq.) Hybrids to Copper Toxicity

“…(-) There is no interaction between the factors tested. (Nair and Chung, 2014). Increasing lignification could happen because there were at least two Cu enzymes in lignin biosynthesis: polyphenol oxidase catalysed the oxidation of phenolics as precursor of lignin, and diamine oxidase provided the H2O2 required for oxidation by peroxidases (Broadley et al, 2012).…”