The Addition of Selenium to the Nutrient Solution Decreases Cadmium Toxicity in Pepper Plants Grown under Hydroponic Conditions

Rafael Perez-Millan,Francisco Garcia-Sanchez,Inma Simon,Marina Alfosea-Simon,Ernesto Alejandro Zavala-Gonzalez,Silvia Simon-Grao,Jose Maria Camara-Zapata,Muhammad Adnan Shahid,Vicente Lidon,Juan Jose Martinez-Nicolas

doi:10.3390/agronomy11101905

Abstract

Cadmium is absorbed by plants rapidly and without control through the same channels as other essential metals, interfering with their transport and utilization. Many studies have shown that selenium could be utilized as a way to avoid this unwanted transport and other negative effects of Cd. For this reason, the present research study was conducted with four treatments (−Cd/−Se, +Cd/−Se, +Cd/+SeF, and +Cd/+SeR) to determine the type of application of Se that is best (foliarly and/or via the root) as regards the reduction of the toxic effects of Cd on plants. Our results showed that the Cd excess in the nutrient solution resulted in a decrease in the total dry biomass of the plants grown under these conditions, and this decrease was due to the reduction of the growth of the shoot (48% +Cd/−Se, 45% +Cd/+SeF, and 38% +Cd/+SeR, relative to −Cd/−Se). This reduction in growth was due to: (i) the toxicity of Cd itself and (ii) the nutritional disequilibrium suffered by the plants. It seems that under hydroponic conditions, the addition of Se to the nutrient solution, and therefore its absorption through the roots (lower antioxidant activity, superoxide dismutase, H2O2 concentration and higher catalase activity), greatly delayed and reduced the toxic effects of Cd on the pepper plants, as opposed to the foliar application of this element.

Highlights

Environmental contamination due to cadmium (Cd) has drastically increased in nature due to the intensification of industrial activities at the end of the 20th century and the beginning of the 21st century, which have progressively affected different ecosystems including agriculture [1]
One of the main sources of Cd toxicity is the consumption of products from contaminated agricultural areas [3], and this toxicity is due to Cd being the only metal whose toxicity threshold is less for humans than for plants
The objective of the present work is (i) to understand how the presence of Cd in the nutrient solution affects pepper plants (Capsicum annum), with respect to growth parameters, the concentration of Cd in the different parts of the plant, gas exchange processes, and oxidative stress systems, and (ii) to determine if the foliar or root application of Se can palliate the negative effects of Cd toxicity, elucidating which physiological and biochemical mechanisms could be involved

Summary

Introduction

Environmental contamination due to cadmium (Cd) has drastically increased in nature due to the intensification of industrial activities at the end of the 20th century and the beginning of the 21st century, which have progressively affected different ecosystems including agriculture [1]. Cadmium is a heavy metal without a biological function, and in humans, animals, and plants, it is toxic in low concentrations [2]. For non-hyperacumulator plants, the threshold of toxicity has been established at 5–10 μM Cd in the nutrient solution for hydroponics-grown crops, and 5.0 mg kg−1 in soil. In plants, this metal has a threshold of toxicity of 3–30 mg kg−1 dry weight [6]

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