Abstract
Cadmium (Cd) is a toxic, biologically non-essential and highly mobile metal that has become an increasingly important environmental hazard to both wildlife and humans. In contrast to conventional remediation technologies, phytoremediation based on legume–rhizobia symbiosis has emerged as an inexpensive decontamination alternative which also revitalize contaminated soils due to the role of legumes in nitrogen cycling. In recent years, there is a growing interest in understanding symbiotic legume–rhizobia relationship and its interactions with Cd. The aim of the present review is to provide a comprehensive picture of the main effects of Cd in N2-fixing leguminous plants and the benefits of exploiting this symbiosis together with plant growth promoting rhizobacteria to boost an efficient reclamation of Cd-contaminated soils.
Highlights
LEGUMES, A PROMISING TOOL FOR CD PHYTOREMEDIATION An increasingly industrialized global economy over the last century has led to a dramatic increase in production and release of hazardous metals to the environment (Gerhardt et al, 2009)
This review summarizes some of the recent advances in this field and highlights the potential of this three partner relationship legume–rhizobia–PGPRs for Cd detoxification
One of the outstanding characteristics of this family is that most legumes have the ability to establish a symbiotic relationship with soil nitrogen-fixing (N2-fixing) rhizobacteria, known collectively as rhizobia, e.g., Rhizobium, Mesorhizobium, Bradyrhizobium, Azorhizobium, Allorhizobium, or Sinorhizobium (Velázquez et al, 2010)
Summary
Oxygen control Reactive oxygen species (ROS) over-production Oxidative damage Antioxidant system deregulation. When legumes have been exposed to high Cd concentrations or long exposure, the high mobility of Cd brought its translocation to shoots and provoked photosynthesis impairment, leaves chlorosis, and oxidative damage in nodules It seems that the nitrogen fixation inhibition related to a severe Cd exposure observed in different legumes like soybean (Balestrasse et al, 2006), white lupin (Carpena et al, 2003), or mung bean (Vigna radiata; Muneer et al, 2012) would be associated to a general plant breakdown rather than to a specific effect of Cd in nodules affecting SNF. The authors showed an increase in total N (52%) and P (89%) uptake and suggested that it was the result of root growth
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