Archives

  • 2018-07
  • 2019-04
  • 2019-05
  • 2019-06
  • 2019-07
  • 2019-08
  • 2019-09
  • 2019-10
  • 2019-11
  • 2019-12
  • 2020-01
  • 2020-02
  • 2020-03
  • 2020-04
  • 2020-05
  • 2020-06
  • 2020-07
  • 2020-08
  • 2020-09
  • 2020-10
  • 2020-11
  • 2020-12
  • 2021-01
  • 2021-02
  • 2021-03
  • 2021-04
  • 2021-05
  • 2021-06
  • 2021-07
  • 2021-08
  • 2021-09
  • 2021-10
  • 2021-11
  • 2021-12
  • 2022-01
  • 2022-02
  • 2022-03
  • 2022-04
  • 2022-05
  • 2022-06
  • 2022-07
  • 2022-08
  • 2022-09
  • 2022-10
  • 2022-11
  • 2022-12
  • 2023-01
  • 2023-02
  • 2023-03
  • 2023-04
  • 2023-05
  • 2023-06
  • 2023-08
  • 2023-09
  • 2023-10
  • 2023-11
  • 2023-12
  • 2024-01
  • 2024-02
  • 2024-03
  • 2024-04

    • Introduction Increasing environmental pollution caused by he

    2022-11-09

    Introduction Increasing environmental pollution caused by heavy metals, originating mainly from industrial processes and urban activities, as well as the widespread application of pesticides, fertilizers, manure and sewage sludge, has posed a serious problem for safe food production and become a potential agricultural and global environmental problem (Bonet et al., 2014; Daş et al., 2016; Zhu et al., 2017a). Among the various heavy metals, Cadmium (Cd) occupies the top position in terms of hazardous effects posed to plants and human health, due to its high toxicity, mobility, and availability for all living organisms (Ali et al., 2015, Clemens et al., 1999, Wael et al., 2015). The deleterious effects following exposure to Cd in humans has been associated with cancers of the prostate, lungs, and testes, renal dysfunction, rhinitis, emphysema, and bone fractures (Jarup and Akesson, 2009). The accumulation of Cd also inhibits growth, development and productivity of plants via impaired amino Fmoc-Ser-OH receptor biosynthesis, inhibition of enzyme activities, induction of oxidative stress, interference with mineral nutrition and metabolic imbalances (Liu et al., 2015, Nagajyoti et al., 2010). The visual symptoms of Cd toxicity in plants are chlorosis and necrosis of leaves, browning of roots and cell apoptosis (Zemanová et al., 2015b). However, plants have evolved a variety of adaptive mechanisms to protect against Cd stress. This is achieved by cellular exclusion, sequestration, chelation osmotic adjustment, metabolic utilization and production of antioxidant systems, etc. (Kushwaha et al., 2016, Li et al., 2016, Rahman et al., 2017, Sytar et al., 2013, Zhang et al., 2015). Nitrogen metabolism is central in the plant response to heavy metals; it has been shown that Cd may interfere with nitrogen metabolism in plants (Chaffei et al., 2004). Upon exposure to metals, plants often synthesize a set of diverse low-molecular weight substances, particularly specific free amino acids (FAA), which are known as compatible solutes, and have been shown to serve as signaling molecules and play an important role in plants varied from acting as osmolyte, radical scavenger, regulation of ion transport, modulating stomatal opening to detoxification of heavy metals (Pavlíková et al., 2014, Sharma and Dietz, 2006, Xu et al., 2012). The changes appearing in free amino acids as a response to different stress factors are important for plant metabolism as they are not only known as precursors and functional components of proteins but also, for most of them, as precursors of other nitrogen containing compounds such as nucleic acids (Rai, 2002). The accumulation of Cd in plant organs cause damages to the photosynthetic apparatus (Gallego et al., 2012). The reduction in the photosynthetic rate results in a limited supply of metabolic energy and therefore to nitrogen assimilation restriction. Nitrogen flow through amino acids can thereby change in response to Cd stress (Zemanová et al., 2015a). Amino acids also affect synthesis and activity of some enzymes, gene expression and redox-homeostasis (Chaffei-Haouari et al., 2009, Islam et al., 2009). Furthermore, amino acids rich in carboxyl, amino, thiol and phenolic groups are involved in the synthesis of glutathione and phytochelatin, which are able to form complex metal cations diminishing its reactivity with other molecules at cellular level, and serving as long-distance metal-chelating compounds (Dave et al., 2013, Ghnaya et al., 2010, Irtelli et al., 2009, Richau et al., 2009). Previous studies have focused attention on the role of the amino acids in Cd tolerance of plants. It has been recorded that Cd accumulation leads to the accumulation of proline in mung, wheat and barley (Leskó and Simon-Sarkadi, 2002; Vassilev and Lidon, 2011; Zhang et al., 2000). However, Costa and Morel (1994) found that Cd induced no accumulation of proline in lettuce but induced specific increases in the levels of asparagine, methionine and lysine. Zoghlami et al. (2011) showed that, in the roots of tomatoes after Cd exposure, asparagine, glutamine and branched chain amino acids (valine, isoleucine, phenylalanine and tryptophane) significantly accumulated; in contrast, few modifications occurred in the leaves in response to Cd, except for tyrosine. Xu et al. (2012) detected that a higher accumulation of proline in S. nigrum supports the observed higher Cd tolerance in S. nigrum than in S. torvum; a high accumulation of hydroxyproline in S. torvum roots may play a protective role in preventing Cd translocation from the roots to the aerial parts of the plant. Zemanová et al., 2013, Zemanová et al., 2014 reported that the major amino acid forms used for nitrogen transport are asparagine and histidine for the higher stress adaptation of A. halleri and glutamate for N. caerulescens. An increase of phenylalanine, threonine, tryptophan, ornithine and a decrease of alanine and glycine were observed in the responses of the two Noccaea metallophytes species to Cd stress (Zemanová et al., 2017). According to the data available in literature, amino acid metabolisms are differently affected by heavy metal treatments, plant species, genotypic difference, and even by different parts of the plant.