**5. Concluding remarks**

A great body of evidence suggests that exposure to 2,4-D or to its ester or salt formulations is associated with a wide range of adverse effects in human and different animal species (Berkley & Magee, 1963; Bortolozzi et al, 2001, 2003; Ferri et al., 2003, 2007; Konjuh et al., 2008; Stürtz et al., 2010).

Oxidative stress may affect the cells as a result of imbalance between the (physiological) production of potentially toxic ROS and some (physiological) scavenging activities (Park et al., 1999). Xenobiotics that interact with one or several complexes of the mitochondrial electron transport system, impairing the normal electron flow, may enhance ROS generation, leading to an imbalance between prooxidant species and cellular antioxidants (Jurado et al., 2011).

This review has analyzed the oxidative stress as a possible mechanism of toxicity by the herbicide 2,4-D. The collected evidence confirms that 2,4-D is an environmental pollutant that induces oxidative stress and could determine important deleterious changes in the development of the neural and reproductive systems in the studied models (Ferri et al., 2007; Bongiovanni et al., 2007, 2011; Pocchettino et al., 2010).

While the reported results showed that 2,4-D induces both necrosis and apoptosis, the evidence suggests that apoptosis would be mediated by or associated to an oxidative imbalance (Bongiovanni et al., 2011). Then, the oxidative stress would produce cytochromec release from mitochondria and a consequent activation of caspase-3 in the affected cells (De Molliner et al., 2002). However, as mitochondria contribute to both apoptosis and necrosis, intracellular ATP and GSH could determine cell death by one or both of these mechanisms (Leist et al., 1997; Yutaka et al., 1997; Qian et al., 1999; Nieminen, 2003; Bongaerts, 2008). Therefore, the 2,4-D cytotoxic actions may involve some permissive effect on either necrosis or apoptosis induction.

Finally, the experimental evidence reported that 2.4-D can not only affect the nervous system or other hormone-sensitive organs, but also exert a very important, deleterious effect on embryonic and fetal development.

#### **6. Acknowledgment**

We thank Prof. Dr. Jose Luis Ferretti for his assistance in writing of the chapter.

### **7. References**

Abdollahi, M., Ranjbar, A., Shadnia, S., Nikfar, S. & Rezaie, A. (2004). Pesticides and oxidative stress: a review. *Medical Science Monitor* , Vol. 10, No. 6, (june 2004), pp.141-147, ISSN 1234-1010.

Cooter, 2001). While apoptosis and necrosis present some early features that may be common to both, mithocondrial disorders could be irreversibly compromised in necrotic, but not in apoptotic neurons (Nicotera & Leist, 1997). This could explain why amphetamine

In summary, 2,4-D would induce necrosis and apoptosis, the latter being possibly mediated

A great body of evidence suggests that exposure to 2,4-D or to its ester or salt formulations is associated with a wide range of adverse effects in human and different animal species (Berkley & Magee, 1963; Bortolozzi et al, 2001, 2003; Ferri et al., 2003, 2007; Konjuh et al.,

Oxidative stress may affect the cells as a result of imbalance between the (physiological) production of potentially toxic ROS and some (physiological) scavenging activities (Park et al., 1999). Xenobiotics that interact with one or several complexes of the mitochondrial electron transport system, impairing the normal electron flow, may enhance ROS generation, leading to an imbalance between prooxidant species and cellular antioxidants

This review has analyzed the oxidative stress as a possible mechanism of toxicity by the herbicide 2,4-D. The collected evidence confirms that 2,4-D is an environmental pollutant that induces oxidative stress and could determine important deleterious changes in the development of the neural and reproductive systems in the studied models (Ferri et al.,

While the reported results showed that 2,4-D induces both necrosis and apoptosis, the evidence suggests that apoptosis would be mediated by or associated to an oxidative imbalance (Bongiovanni et al., 2011). Then, the oxidative stress would produce cytochromec release from mitochondria and a consequent activation of caspase-3 in the affected cells (De Molliner et al., 2002). However, as mitochondria contribute to both apoptosis and necrosis, intracellular ATP and GSH could determine cell death by one or both of these mechanisms (Leist et al., 1997; Yutaka et al., 1997; Qian et al., 1999; Nieminen, 2003; Bongaerts, 2008). Therefore, the 2,4-D cytotoxic actions may involve some permissive effect

Finally, the experimental evidence reported that 2.4-D can not only affect the nervous system or other hormone-sensitive organs, but also exert a very important, deleterious effect

Abdollahi, M., Ranjbar, A., Shadnia, S., Nikfar, S. & Rezaie, A. (2004). Pesticides and

oxidative stress: a review. *Medical Science Monitor* , Vol. 10, No. 6, (june 2004),

We thank Prof. Dr. Jose Luis Ferretti for his assistance in writing of the chapter.

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2007; Bongiovanni et al., 2007, 2011; Pocchettino et al., 2010).

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**6. Acknowledgment** 

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**5. Concluding remarks** 

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**18** 

*Brazil* 

**Weed Population Dynamics** 

*1Federal University of Tocantins* 

Aurélio Vaz De Melo1, Rubens Ribeiro da Silva1, Hélio Bandeira Barros1 and Cíntia Ribeiro de Souza2

*2Federal Institute of Education, Science and Technology of Pará* 

Clearly, the growing infestation of weeds in agricultural systems causes damage to crops, with sharp declines in productivity, either by direct competition for factors of production, whether by allelopathic compounds released into the soil (MARTINS and PITELLI, 1994). There are many factors related to population dynamics of these plants. However this chapter will be referred to those who, according to research, seem to be the most important.

In various cultures was observed the influence of farming system, being of fundamental importance to understand these dynamics through studies on the floristic composition and phytosociological structure of the same. The cultivation of maize intercropped with tropical forages in the system of direct planting can reduce the incidence of weeds due to the high biomass production and allelopathy provided by surface deposition of straw on the soil. The presence of *B. brizantha* intercropping reduced weed density. Therefore, the use of intercropping maize with *B. brizantha* provides control rate of 95% of the weeds in the soil

A survey of weeds in conventional farming sunflower family Poaceae was the most representative among species (SILVA et al., 2010). In the experiment carried out by MARQUES et al. (2010) the plants originate in poultry farming sprouts in cowpea had the highest rates of importance values. However, they are dependent on the season and the

Mechanized harvesting of raw cane enables the maintenance of the layer of straw on the surface, so by reducing the movement of soil and alter the dynamics of herbicides. These changes promote changes in microclimatic conditions, which in turn affect the composition of specific weeds. In this culture, the population dynamics of weeds in no-tillage system reduces up to 531% the incidence of weeds compared to the conventional system after treatment with herbicides. This provides 27% reduction in the productivity of cane sugar in

The results obtained by VAZ-DE-MELO et al. (2007) showed that the practices adopted in growing organic green corn under no-tillage system, provide the appropriate management of weeds while with adoption of soil cover with oat straw. Among the weed

**2. Factors influencing the population dynamics of weed** 

**1. Introduction** 

(BORGHI et al., 2008).

continuity of the system.

conventional tillage soil (DUARTE JR et al., 2009).

