**3. Antioxidant system in plants**

Plants have evolved a complex antioxidant system composed by both non-enzymatic and enzymatic components, to prevent the harmful effects of ROS.

Low-molecular-mass metabolites soluble in both aqueous and lipid phases lipid with high ROS reactivity such as ascorbate, glutathione tocopheroles, flavonoids, alkaloids, carotenoids, proline and amines, form non-enzymatic part of the antioxidant system (Apel & Hirt, 2004; Sharma and Dietz, 2006).

other cystein thiol modification mediated by nitric oxide, reactive nitrogen species (RNS) and glutathione. RNS are generated by the interaction between nitric oxide and ROS. (Costa et al., 2003; Halliwell, 2006). Carbonylation, a common oxidative protein modification affecting particularly Arg, His, Lys, Pro, Thr, and Trp; and conjugation with peroxidation PUFA products, mainly with HNE, are other oxidative protein modifications (Shacter, 2000;

The generation of 8-Hydroxyguanine is the most common DNA modification induced by

all (Wiseman & Halliwell, 1996). Chloroplastic and mitochondrial DNAs are into the two major source of ROS where potentially high rates of modification might occur (Thorslund et al., 2002). Another indirect oxidative modification to DNA is the conjugation of MDA with guanine (Jeong, 2005). The DNA oxidative modification could induce changes in cytosines methylation patterns, and then in the regulation of gene expressions. ROS-induced DNA

In spite of its toxic effects, increasing evidence indicates that ROS are signaling molecules that participate in many processes, such as cell cycle, cell elongation, cell death, plant growth and development, senescence, hormone signaling, responses to biotic and abiotic stress and in symbiotic interaction with microorganisms (Bustos et al., 2008; Mittler et al., 2004; Muñoz et al. 2011, submitted; Rodriguez et al., 2010). The H2O2 molecular properties make it a good second messenger that could cross membrane by diffusion or aquaporins. However, all ROS can act as signaling molecules directly or by oxidized product. NADPH oxidase complex, the main source of apoplastic ROS, has a key role in oxidative signaling

The dual role of ROS, as toxic or signaling molecules, depends on the ratio and subcellular location of its generation, thus the tight regulation of the steady-state level of ROS in different subcellular compartments has both signaling and oxidative damage protection purposes. The function of ROS as signaling molecules is intrinsically related to the interaction with non-enzymatic antioxidants, such as ascorbate and glutathione, which are

The relationship among ROS, antioxidants, reducing equivalents, sugars, the redox state of chloroplastic and mitochondria electron transport chains are major determinants of the cellular redox state, which has a critical function in the environmental perception and modulation of defense, acclimation and tolerance responses (Foyer & Noctor, 2005 a; 2005b;

Plants have evolved a complex antioxidant system composed by both non-enzymatic and

Low-molecular-mass metabolites soluble in both aqueous and lipid phases lipid with high ROS reactivity such as ascorbate, glutathione tocopheroles, flavonoids, alkaloids, carotenoids, proline and amines, form non-enzymatic part of the antioxidant system (Apel

redox buffers and also signal molecules *per se* (Foyer & Noctor 2005 a, 2005b).

Lascano et al., 2003; Melchiorre et al., 2009; Robert et al., 2009).

enzymatic components, to prevent the harmful effects of ROS.

**3. Antioxidant system in plants** 

& Hirt, 2004; Sharma and Dietz, 2006).

•−

OH, being the formic acid the main

do not react at

ROS. The nucleotide bases are attacked by. OH and 1O2 while H2O2 and O2

modification seems to be a not completely random process (Halliwell, 2006).

Carbohydrates can be oxidatively modified by .

breakdown product of sugar oxidation (Isbell et al., 1973).

Winger et al., 2005).

(Sagi & Fhlur, 2004).

Superoxide dismutase (SOD) (E.C.: 1.15.1.1), ascorbate peroxidase (APX) (E.C.: 1.11.1.11), catalase (CAT) (EC 1.11.1.6), and glutathione reductase (GR) (E.C.: 1.6.4.2) are key antioxidant enzymes that modulate the concentration of two of the Haber/Weiss and Fenton reaction substrates, O2 •- and H2O2, preventing the formation of the highly toxic . OH radical (Asada, 1999). Approximately, 80% of SOD, GR, and APX activity is located in the chloroplast (Asada, 1999). CAT activity is located in peroxisomes and mitochondria (Scandalios, 1994). SOD catalyses the disproportionation of O2 •- to H2O2, and is present in multiple isoforms: copper/zinc (CuZn-SOD), iron (Fe-SOD) and manganese (Mn-SOD) (Bowler et al, 1992). In most plants, CuZn-SOD and Fe-SOD are present in the chloroplasts, CuZn-SOD in the cytosol and Mn-SOD in mitochondria (Casano et al., 1997; Scandalios, 1993). Degradation of H2O2, in the chloroplasts and in the cytosol is carried out by the ascorbate-glutathione cycle, which involves APX and GR activities (Lascano et al., 1999, 2003). APX has chloroplastic and cytosolic isoforms, and catalyses the conversion of H2O2 to water using ascorbate as electron donor (Asada, 1999).

Reduced glutathione (GSH) and ascorbic acid are the most important soluble non-enzymatic antioxidants and in chloroplasts they are present at millimolar concentrations (Noctor & Foyer, 1998). Ascorbate acts as a ROS quencher and it is involved in the regenerations of tocopherol and violoxanthine depoxidase activity of xanthophylls cycle (Noctor & Foyer, 1998). Reduced glutathione is a tripeptide -glutamylcysteinyl glycine (-Glu-Cys-Gly) involved in: direct reaction with ROS, the regeneration of the ascorbate pool and as electron donor of glutaredoxins which are linked to type II peroxiredoxin activity. Likewise, GSH participates in the glutathionylation, a post-transcriptional modification of protein thiols groups that regulates the function of proteins like glyceraldehyde-3-phosphate dehydrogenease and thioredoxin activities (Michelet et al., 2005; Zaffagnini et al., 2007). The reduction of oxidized glutathione is NADPH-dependent and carried out by GR, a ubiquitous flavoenzyme with many isoforms, located in chloroplasts, cytosol, and mitochondria (Lascano et al., 2001; Tanaka et al., 1994).

Other more recently identified components of enzymatic antioxidant system are peroxiredoxins and glutathione peroxidase, non-heme-containing peroxidase which activity depend on cystein residues (Bryk et al., 2000; König et al., 2003).

## **4. The use of paraquat in stress response studies**

Plants as sessile organism are permanently exposed to changing environment that become stressful conditions affecting their growth, development and productivity. Tolerance to environmental stress is a major selection criterion in plant breeding. The cellular and molecular tolerance mechanisms of plants to different stresses have been intensively studied.

Reactive oxygen species are produced as byproduct of normal aerobic metabolism and the life under aerobic conditions is strictly dependent on the presence of antioxidant system. Nowadays, it is widely accepted that the generation of ROS is enhanced under abiotic and biotic stress conditions. Depending on stress intensity and its associated-ROS levels the plant responses range from tolerance to death.

Likewise, the positive response of the antioxidant system correlates, in part, with the tolerance to many different environmental stress conditions. ROS and antioxidant system

Paraquat: An Oxidative Stress Inducer 141

symbiosis were studied using different dose of paraquat to induce oxidative stress in nodules. Paraquat produced cellular redox imbalance leading to an inhibition of biological nitrogen fixation (BNF). The low paraquat dose provoked BNF decline, preceded by a decrease in sucrose synthase gene expression protein content and activity, while high paraquat induced a faster and more pronounced BNF inhibition, coinciding with a decline in sucrose synthase and also with a reduction in leghaemoglobin content. These results support the occurrence of two regulation pathways for BNF under oxidative stress, one of these involving carbon shortages and the other involving leghaemoglobin /oxygen flux

To date, several mutants, ecotypes, and biotypes with paraquat resistance have been characterized in a few plant species. Paraquat-resistant mutants have been shown to be cross tolerant to other oxidative stress conditions and have been used to study the tolerance to

There are several paraquat-resistant *Arabidopsis* mutants. Photoautotrophic salt tolerate 1 (*pst1*), an *Arabidopsis* mutant that can grow under high salt concentrations, is nearly 10 times more tolerant to paraquat than wild-type seedlings. This mutant, which is also tolerant to high light intensities exhibits higher SOD and APX activities under paraquat, salt, and high

The paraquat-resistant *Arabidopsis thaliana* mutant, allelic to the ozone sensitive mutant *rcd1-1*( radical-induced cell death1-1) (Overmyer et al., 2000), called *rcd1-2*, is also tolerant to UV-B and freezing. The tolerance in this mutant is also related to higher levels of the ROS-scavenging enzymes, particularly chloroplastic CuZn-SOD and APX, and also with an increased accumulation of flavonoids (Fujibe et al, 2004). *Arabidopsis* Cvi ecotype also shows a higher resistance to paraquat, which seems to be determined by a new allele of plastidic

*Gigantea*, a late-flowering *Arabidopsis* mutant, is resistant to paraquat (Kurepa et al., 1998), however, the resistance mechanism remains unknown (Huq et al., 2000). In the broadleaf weed *Archoteca calendula* (L) paraquat tolerance has been associated with increases in antioxidant defense. This species also exhibit cross tolerance to other stress conditions (Soar

*Arabidopsis paraquat resistant2-1 (par2-1) mutant* show an anti-cell death phenotype. Paraquat treatment induce similar superoxide production in *par2-1* and wild-type plants, suggesting that PAR2 acts downstream of superoxide to regulate cell death. *par2-1* encode a Snitrosoglutathione reductase (GSNOR) that catalyze a major biologically active nitric oxide species, S-nitrosoglutathione. Compared to wild type, *par2-1* mutant showed higher nitric oxide level, suggesting that nitric oxide level and nitrosylation protein modification

Other paraquat-resistant genotypes have also been reported; like the grass weed *Hordeum glaucum* (Lasat et al., 1997) and *Conyza bonariensis* (Fuerst et al., 1985; Norman et al., 1994). The resistance mechanism seems to be related to a higher herbicide compartmentalization in root vacuoles of the resistant biotype than in the susceptible one. On the contrary, the amount of paraquat accumulated in the cytoplasm of the susceptible biotype was double

(Marino et al., 2006, 2008).

**4.1 Paraquat resistant mutants** 

CuZnSOD (Abarca et al., 2001).

et al., 2003).

other photooxidative stress condition (Tsugane et al., 1999).

light intensities treatments (Tsugane et al., 1999).

regulates cell death in plant cells (Chen et al., 2009).

that found in the resistant biotype.

are central components of the cross-tolerance phenomenon which states that a tolerant genotype to one stress condition could be also tolerant to other kinds of stress.

Paraquat treatments have been frequently used, as a potent oxidative stress inducer, in many different basic studies like: oxidative stress tolerance and cross tolerance responses associated with the antioxidant system responses (Lascano et al., 1998, 2001, 2003), forward and reverse genetic approaches to study the function of different antioxidant system components (Melchiorre et al., 2009 and references therein,) ROS signaling (Robert et al., 2009), ROS and NO-induced cell death (Tarantino et al., 2005), and to mimic the drought effect on carbon and nitrogen metabolism of nodules (Marino et al., 2006).

Several attempts made to enhance tolerance photooxidative stress conditions have been tested with paraquat treatments. These have involved the overexpression of enzymes associated with the Asada-Halliwell pathway including SOD (Arisi et al., 1998; Bowler et al, 1991; McKersie et al., 1999; Melchiorre et al., 2009; Perl et al., 1993; Pitcher et al, 1991; Sen Gupta et al., 1993;Tepperman et al, 1990; Van Camp et al.,1996), and GR (Aono et al., 1991, 1993; Creissen et al., 1995; Foyer et al., 1991, 1995; Melchiorre et al., 2009). The tolerance to different oxidative stress conditions was dependent on the copy numbers and overexpression levels; the isoform overexpressed; the subcellular location where the overexpressions were targeted; and the induction of other antioxidant enzymes. The results of chloroplasts-targeted Mn-SOD or GR overexpression in wheat chloroplasts, suggest that antioxidant enzyme overexpression effects on tolerance response not only depend on their antioxidant capacities but also on their effects on the cellular redox state, which modulates the responses to photooxidative stress in a pathway where apoplastic superoxide generation could be involved (Melchiorre et al., 2009). The photooxidative activations of NADPH oxidase complex, the main source of apoplastic ROS, can be mimicked by paraquat treatment (Robert et al., 2009).

Paraquat has also been used as an efficient inducer of cell death in both animal and plant cells (Dodge, 1971; Suntres, 2002). The cell death processes in plants are major regulatory mechanism of growth, development, and responses to biotic and abiotic stresses (Lam et al., 2001; Pennel & Lamb, 1997). Environmental or developmental conditions where cellular redox balance is disturbed and significant ROS accumulation occurred, could lead to the induction of cell death processes (Dat et al., 2000). In this context, two type of ROSassociated stress intensity-dependent death can be defined: Ordered or Programmed Cell Death (PCD) when the cell maintains the membrane and energy generation systems, and Disordered or Necrosis, when these systems are overwhelmed by the oxidative burst. Continuous or transient light-dependent H2O2 accumulation, provoke necrosis or PCD, respectively indicating the existence of a ROS levels threshold below which PCD is triggered and above which necrotic cell death prevail (Montillet et al., 2005).

Programmed Cell Death in plant cells shares some similarities with that of animal cells, like organelle degeneration, nuclear condensation, nuclear DNA fragmentation and eventually cell shrinkage. Interestingly, animal anti-apoptotic protein (Bcl-2, Bcl-xL, and CED-9) expressed in plant, prevented apoptosis-like death mediated by chloroplasts photooxidadative stress induced by paraquat (Chen & Dickman, 2004; Mitsuhara et al., 1999).

The *in vivo* relationship between ROS-associated to environmental stress condition like drought and biological nitrogen fixation (BNF) inhibition in the legume–Rhizobium

are central components of the cross-tolerance phenomenon which states that a tolerant

Paraquat treatments have been frequently used, as a potent oxidative stress inducer, in many different basic studies like: oxidative stress tolerance and cross tolerance responses associated with the antioxidant system responses (Lascano et al., 1998, 2001, 2003), forward and reverse genetic approaches to study the function of different antioxidant system components (Melchiorre et al., 2009 and references therein,) ROS signaling (Robert et al., 2009), ROS and NO-induced cell death (Tarantino et al., 2005), and to mimic the drought

Several attempts made to enhance tolerance photooxidative stress conditions have been tested with paraquat treatments. These have involved the overexpression of enzymes associated with the Asada-Halliwell pathway including SOD (Arisi et al., 1998; Bowler et al, 1991; McKersie et al., 1999; Melchiorre et al., 2009; Perl et al., 1993; Pitcher et al, 1991; Sen Gupta et al., 1993;Tepperman et al, 1990; Van Camp et al.,1996), and GR (Aono et al., 1991, 1993; Creissen et al., 1995; Foyer et al., 1991, 1995; Melchiorre et al., 2009). The tolerance to different oxidative stress conditions was dependent on the copy numbers and overexpression levels; the isoform overexpressed; the subcellular location where the overexpressions were targeted; and the induction of other antioxidant enzymes. The results of chloroplasts-targeted Mn-SOD or GR overexpression in wheat chloroplasts, suggest that antioxidant enzyme overexpression effects on tolerance response not only depend on their antioxidant capacities but also on their effects on the cellular redox state, which modulates the responses to photooxidative stress in a pathway where apoplastic superoxide generation could be involved (Melchiorre et al., 2009). The photooxidative activations of NADPH oxidase complex, the main source of apoplastic ROS, can be mimicked by paraquat

Paraquat has also been used as an efficient inducer of cell death in both animal and plant cells (Dodge, 1971; Suntres, 2002). The cell death processes in plants are major regulatory mechanism of growth, development, and responses to biotic and abiotic stresses (Lam et al., 2001; Pennel & Lamb, 1997). Environmental or developmental conditions where cellular redox balance is disturbed and significant ROS accumulation occurred, could lead to the induction of cell death processes (Dat et al., 2000). In this context, two type of ROSassociated stress intensity-dependent death can be defined: Ordered or Programmed Cell Death (PCD) when the cell maintains the membrane and energy generation systems, and Disordered or Necrosis, when these systems are overwhelmed by the oxidative burst. Continuous or transient light-dependent H2O2 accumulation, provoke necrosis or PCD, respectively indicating the existence of a ROS levels threshold below which PCD is triggered

Programmed Cell Death in plant cells shares some similarities with that of animal cells, like organelle degeneration, nuclear condensation, nuclear DNA fragmentation and eventually cell shrinkage. Interestingly, animal anti-apoptotic protein (Bcl-2, Bcl-xL, and CED-9) expressed in plant, prevented apoptosis-like death mediated by chloroplasts photooxidadative stress induced by paraquat (Chen & Dickman, 2004; Mitsuhara et al.,

The *in vivo* relationship between ROS-associated to environmental stress condition like drought and biological nitrogen fixation (BNF) inhibition in the legume–Rhizobium

and above which necrotic cell death prevail (Montillet et al., 2005).

genotype to one stress condition could be also tolerant to other kinds of stress.

effect on carbon and nitrogen metabolism of nodules (Marino et al., 2006).

treatment (Robert et al., 2009).

1999).

symbiosis were studied using different dose of paraquat to induce oxidative stress in nodules. Paraquat produced cellular redox imbalance leading to an inhibition of biological nitrogen fixation (BNF). The low paraquat dose provoked BNF decline, preceded by a decrease in sucrose synthase gene expression protein content and activity, while high paraquat induced a faster and more pronounced BNF inhibition, coinciding with a decline in sucrose synthase and also with a reduction in leghaemoglobin content. These results support the occurrence of two regulation pathways for BNF under oxidative stress, one of these involving carbon shortages and the other involving leghaemoglobin /oxygen flux (Marino et al., 2006, 2008).

#### **4.1 Paraquat resistant mutants**

To date, several mutants, ecotypes, and biotypes with paraquat resistance have been characterized in a few plant species. Paraquat-resistant mutants have been shown to be cross tolerant to other oxidative stress conditions and have been used to study the tolerance to other photooxidative stress condition (Tsugane et al., 1999).

There are several paraquat-resistant *Arabidopsis* mutants. Photoautotrophic salt tolerate 1 (*pst1*), an *Arabidopsis* mutant that can grow under high salt concentrations, is nearly 10 times more tolerant to paraquat than wild-type seedlings. This mutant, which is also tolerant to high light intensities exhibits higher SOD and APX activities under paraquat, salt, and high light intensities treatments (Tsugane et al., 1999).

The paraquat-resistant *Arabidopsis thaliana* mutant, allelic to the ozone sensitive mutant *rcd1-1*( radical-induced cell death1-1) (Overmyer et al., 2000), called *rcd1-2*, is also tolerant to UV-B and freezing. The tolerance in this mutant is also related to higher levels of the ROS-scavenging enzymes, particularly chloroplastic CuZn-SOD and APX, and also with an increased accumulation of flavonoids (Fujibe et al, 2004). *Arabidopsis* Cvi ecotype also shows a higher resistance to paraquat, which seems to be determined by a new allele of plastidic CuZnSOD (Abarca et al., 2001).

*Gigantea*, a late-flowering *Arabidopsis* mutant, is resistant to paraquat (Kurepa et al., 1998), however, the resistance mechanism remains unknown (Huq et al., 2000). In the broadleaf weed *Archoteca calendula* (L) paraquat tolerance has been associated with increases in antioxidant defense. This species also exhibit cross tolerance to other stress conditions (Soar et al., 2003).

*Arabidopsis paraquat resistant2-1 (par2-1) mutant* show an anti-cell death phenotype. Paraquat treatment induce similar superoxide production in *par2-1* and wild-type plants, suggesting that PAR2 acts downstream of superoxide to regulate cell death. *par2-1* encode a Snitrosoglutathione reductase (GSNOR) that catalyze a major biologically active nitric oxide species, S-nitrosoglutathione. Compared to wild type, *par2-1* mutant showed higher nitric oxide level, suggesting that nitric oxide level and nitrosylation protein modification regulates cell death in plant cells (Chen et al., 2009).

Other paraquat-resistant genotypes have also been reported; like the grass weed *Hordeum glaucum* (Lasat et al., 1997) and *Conyza bonariensis* (Fuerst et al., 1985; Norman et al., 1994). The resistance mechanism seems to be related to a higher herbicide compartmentalization in root vacuoles of the resistant biotype than in the susceptible one. On the contrary, the amount of paraquat accumulated in the cytoplasm of the susceptible biotype was double that found in the resistant biotype.

Paraquat: An Oxidative Stress Inducer 143

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Additionally, paraquat tolerance has been associated with the expression of transporters able to carry molecules with similar chemical structure or charge distribution to paraquat, like polyamines (Tachihara et al., 2005). Pharmacological treatments with blockers of proton pump ATPases, such us nitrate, carbonyl-cyanide-m-chlorophenylhydrazone (CCCP) and N4N1- dicyclohexylcarbodiimide (DCCD) were used in order to study their effects on paraquat moving into inactive compartments in *C. canadiensis* (Jóri et al., 2007). Recovery after paraquat treatment in tolerant biotypes was strongly inhibited by nitrate, as nitrate selectively blocks ATPases in the vacuoles -responsible for energy supplies to vacuolar membranes- the results suggested that paraquat sequestration uses energy from the proton gradient (Jóri et al., 2007).

Regarding the relationship between paraquat tolerance and leaf age, some studies have shown that young leaves are more tolerant than mature ones (Kuk et al., 2006; Ohe et al., 2005), it is worth nothing that responses are closely related with detoxify mechanism and antioxidative responses as well as with morphological leaf characteristics such as epicuticular wax content and leaf cuticule development which is the first and most significant barrier for foliar-applied chemicals. Although damage originated by paraquat treatment in *Cucurbita spp* varied among cultivars, the injury provoked by herbicide application was lower in younger leaves than in older ones as it was observed by lesser conductivity values and malondialdehide production which indicate membrane damage with cellular leakage and membrane lipid peroxydation respectively. These responses correlated also with higher antioxidant activity and increases in ascorbate content as well as with higher epicuticular wax in young leaves (Yeol Yoon , 2011).

#### **5. Conclusion**

Paraquat is potent oxidative stress inducer, which beyond the widely use as desiccant herbicide, it has been a very useful tool in plant biology basic research. Many aspect of oxidative stress in plants, the toxic and signaling roles of ROS, the native and transgenic plant tolerance/susceptibility responses to many environmental stress conditions, the cross tolerance phenomenon and different cell death processes have been studied using paraquat treatments.

#### **6. References**


Additionally, paraquat tolerance has been associated with the expression of transporters able to carry molecules with similar chemical structure or charge distribution to paraquat, like polyamines (Tachihara et al., 2005). Pharmacological treatments with blockers of proton pump ATPases, such us nitrate, carbonyl-cyanide-m-chlorophenylhydrazone (CCCP) and N4N1- dicyclohexylcarbodiimide (DCCD) were used in order to study their effects on paraquat moving into inactive compartments in *C. canadiensis* (Jóri et al., 2007). Recovery after paraquat treatment in tolerant biotypes was strongly inhibited by nitrate, as nitrate selectively blocks ATPases in the vacuoles -responsible for energy supplies to vacuolar membranes- the results suggested that paraquat sequestration uses energy from the proton

Regarding the relationship between paraquat tolerance and leaf age, some studies have shown that young leaves are more tolerant than mature ones (Kuk et al., 2006; Ohe et al., 2005), it is worth nothing that responses are closely related with detoxify mechanism and antioxidative responses as well as with morphological leaf characteristics such as epicuticular wax content and leaf cuticule development which is the first and most significant barrier for foliar-applied chemicals. Although damage originated by paraquat treatment in *Cucurbita spp* varied among cultivars, the injury provoked by herbicide application was lower in younger leaves than in older ones as it was observed by lesser conductivity values and malondialdehide production which indicate membrane damage with cellular leakage and membrane lipid peroxydation respectively. These responses correlated also with higher antioxidant activity and increases in ascorbate content as well as

Paraquat is potent oxidative stress inducer, which beyond the widely use as desiccant herbicide, it has been a very useful tool in plant biology basic research. Many aspect of oxidative stress in plants, the toxic and signaling roles of ROS, the native and transgenic plant tolerance/susceptibility responses to many environmental stress conditions, the cross tolerance phenomenon and different cell death processes have been studied using paraquat

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dismutase in transformed poplar modifies the regulation of photosynthesis at low

with higher epicuticular wax in young leaves (Yeol Yoon , 2011).

gradient (Jóri et al., 2007).

**5. Conclusion** 

treatments.

**6. References** 

CO2 partial pressures or following exposure to the prooxidant herbicide methyl viologen. *Plant Physiol.* 117, 565–574


Paraquat: An Oxidative Stress Inducer 145

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**9** 

*Diamantina, MG,* 

*Brasil* 

**Herbicides and the Aquatic Environment** 

Valdemar Luiz Tornisielo1 and José Barbosa dos Santos2 *1Laboratório de Ecotoxicologia, Centro de Energia Nuclear na Agricultura,* 

*2Universidade Federal dos Vales do Jequitinhonha e Mucuri – UFVJM,* 

The quality of water resources is perhaps currently the most discussed topic when it comes to environmental preservation, since aquatic ecosystems have been suffering changes worldwide in most cases irreversible. Such changes are often associated with human activities such as deforestation, release of industrial and domestic effluents, and even the use of pesticides in agricultural fields, which is one of sources that most contributes to the

Pesticides are important to the agricultural system. However, it is crucial that they be used with responsibility in order to preserve the quality of the final product and the natural resources that

Pesticides are products whose function is to eliminate organisms causing damage to agricultural crops thus ensuring high productivity. Their classification is made according to target species (insecticides, herbicides, fungicides, acaricides, nematicides, etc..) (Alves-Silva & Oliveira, 2003, Sanches et al., 2003), patter of use (defoliants, repellents, and others) (Alves-Silva & Oliveira, 2003; Laws, 1993; Sanches et al., 2003), mechamisns of action (acetylcholinesterase inhibitor, anticoagulants, etc) (Alves-Silva & Oliveira, 2003) or chemical structure (pyretroids, organophosphates, carbamates, etc) (Alves-Silva & Oliveira,

Although these molecules, when applied, have target organisms as their final destination, according to Macedo (2002) 99% of applied pesticides go into the air, water and soil, ie, only 1% reaches its target. This finding is quite disturbing as the world population grows; it means that the use of pesticides will increase (thus increasing food productivity) and natural

Pesticides started to become popular in the middle of the Second World War, when the world discovered the DDT. The ease of accesses of this product and its low cost made it to

support the production, especially soil and water (Oliveira Junior & Regitano, 2009).

resources will remain under intense threat from these molecules.

**1. Introduction** 

2003; Laws, 1993).

fall of quality of water resources.

**2. Pesticides market in Brazil** 

*Universidade de São Paulo – CENA/USP, Piracicaba, SP,* 

Rafael Grossi Botelho1, João Pedro Cury2,

