**5. Conclusions**

Furthermore, the increased antioxidant activity has been reported to lead to better performance or tolerance response to several stresses. Using transgenic approaches, several species were studied aiming at the improvement of tolerance to stress enhancing antioxidant capacity of antioxidant genes. Table 1 shows some examples of the successful and positive responses obtained with regard to increased tolerance to cold, drought, heat, salt, hydrogen peroxide, methyl viologen, and metals stresses (Table 1). Improved tolerance using antioxidant genes are attributed by high antioxidant activity and more efficient ROS elimination. Plants express‐ ing or overexpressing one or more antioxidant genes have more antioxidant capacity; conse‐ quently, plants can more efficiently eliminate excess ROS and protect their cellular components against toxic effects of ROS produced during the exposure to stress. As a consequence, plants

**Gene Native specie Target specie Stress tolerance Reference**

*Puccinellia tenuiflora Arabidopsis thaliana* salinity, hydrogen

*Jatropha curcas Nicotiana tabacum* salinity [40] *Hordeum vulgare Arabidopsis thaliana* zinc, cadmium [41]

*Pisum sativum Oryza sativa* drought [44]

*Brassica juncea Nicotiana tabacum* cadmium [47] *Triticum aestivum Oryza sativa* cold [48]

*Suaeda salsa Arabidopsis thaliana* salinity, cold [52]

*Acanthus ebracteatus Oryza sativa* salinity [54] *Avicennia marina Nicotiana tabacum* salinity [55]

*Oryza sativa Nicotiana tabacum* salinity, water, PEG-

*Catalase Brassica oleracea Arabidopsis thaliana* heat [46]

*Festuca arundinacea Festuca arundinacea* heat, methyl

*reductase Malpighia glabra Nicotiana tabacum* salinity [53]

peroxide [39]

peroxide [49]

viologen [50]

viologen [51]

[45]

*bolleana* salinity [43]

treatment

*Ascorbate peroxidase Brassica campestris Arabidopsis thaliana* heat [38]

*Superoxide dismutase Arachis hypogaea Nicotiana tabacum* salinity, drought [42]

*Tamarix androssowii Populus davidiana* x *P.*

*Glutathione peroxidase Triticum aestivum Arabidopsis thaliana* salinity, hydrogen

*Peroxiredoxins Solanum tuberosum Solanum tuberosum* heat, methyl

*Monodehydroascorbate*

suffer less oxidative injury and can tolerate a stress condition more effectively.

472 Abiotic and Biotic Stress in Plants - Recent Advances and Future Perspectives

Plants activate antioxidant defense mechanisms under stresses, which helps in the mainte‐ nance of the structural integrity of the cell components and presumably alleviates oxidative damage. Several antioxidant enzymes contribute to plant defense. The manipulation of ROSscavenging enzyme systems is a worthwhile approach to produce transgenic plants with enhanced tolerance to a wide range of stress conditions; however, this needs to be further explored as many enzymes and isoforms can be involved, and ROS is only one of the potential parameters of plant tolerance against environmental variations and biotic stresses.
