In this study, responses of wild species of potato to NaCl stress were investigated in vitro. In S. stoloniferum and S. bulbosum, length of the shoot, fresh and dry weight, photosynthetic pigments, K ? concentration, K ? /Na ? ratio, ascorbate pool, anthocyanin, and phenolic and flavonoid compounds were decreased in response to salinity. In these species, salinity increased the level of Na ? , lipid peroxidation, proline and ion leakage percentage. In S. acaule, the length of the shoot, and fresh and dry weight were not affected by salinity. Photosynthetic pigments, Na ? concentration, proline, flavonoid and phenolic compounds quantities were increased and K ? /Na ? ratio were decreased. K ? concentration, lipid peroxidation, ascorbate pool, anthocyanin and ion leakage were not changed by NaCl stress. Superoxide dismutase, guaiacol peroxidase, ascorbate peroxidase and catalase activities were increased in all species. The results suggest that the non-enzymatic antioxidant capacity in S. acaule (salt tolerant) is more important than the enzymatic antioxidant capacity in comparison with the other species.
Pepper (Capsicum annuum L.) plants were sprayed with salicylic acid (SA) and treated with ultraviolet radiation UV-A (320-390 nm), UV-B (312 nm), and UV-C (254 nm) of 6.1, 5.8, and 5.7 W m -2 , respectively. UV significantly reduced contents of chlorophyll (Chl) a and b, and carotenoids (Car). SA treatment moderated Chl and Car reduction in plants treated with UV-B and UV-C. The quantity of antocyanins, flavonoids, rutin, and UV-absorbing compounds in plants that were treated with UV-B, UV-C, and SA were significantly increased. Foliar spray of SA counteracted the UV effects on pepper.
Compounds which are able to reduce the damaging effects of various stresses such as drought should be of great importance. In this research we have used arginine pretreatment and the effect of this compound on alleviation of oxidative damages under drought stress has been investigated. Our findings showed that arginine pretreatment reduced the lipid peroxidation when water stress was imposed. In drought stressed plants, H 2 O 2 increased and the activity of antioxidative enzymes were elevated over the controls, while glutathione reductase (GR) activity decreased. When plants pretreated with arginine, activity of catalase and guaiacol peroxidase decreased while the activity of superoxide dismutase (SOD), ascorbate peroxidase, and GR increased. Drought stress decreased ascorbate and reduced glutathione and increased dehydroascorbate. Opposite results were obtained after arginine pretreatment. When arginine was used as a precursor of nitric oxide (NO), the amelioration of the drought effects which was observed could well be the indication that these effects may be related to NO production. To prove that, we applied arginine'Nw-nitro-l-arginine methyl ester (LNAM) and on many parameters, arginine and arginine'LNAM pretreatment had the same effects and it seems that in these situations other pathways of arginine metabolism rather than nitric oxide synthase may be activated
Osmotic stress associated with drought and salinity is a serious problem that inhibits the growth of plants mainly due to disturbance of the balance between production of ROS and antioxidant defense and causes oxidative stress. In this research, sodium nitroprusside (SNP) was used as NO donor in control and droughtstressed plants, and the role of NO in reduction of oxidative damages were investigated. In this study, we observed that SNP pretreatment prevented drought-induced decrease in RWC and membrane stability index, increase in lipid peroxidation and lipoxygenase activity and increase in hydrogen peroxide content. However, pretreatment of plants with SNP and phenyl 4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (a NO scavenger) reversed the protective effects of SNP suggesting that protective effect by SNP is attributable to NO release. In addition, the relationship between these defense mechanisms and activity of antioxidant enzymes were checked. Results showed that in drought-stressed plants ascorbate peroxidase (APX), guaiacol peroxidase (GPX) and catalase activities were elevated over the controls, while GR decreased under drought condition. Activity of GPX was inhibited under SNP pretreatment in drought-stressed plants specially, while the activity of APX and GR increased under SNP pretreatment and it seems that under this condition APX had a key role of detoxification of ROS in tomato plants. This result corresponded well with ASA and total acidsoluble thiols content. Therefore, reduction of droughtinduced oxidative damages by NO in tomato leaves is most likely mediated through either NO ability to scavenge active oxygen species or stimulation of antioxidant enzyme such as APX.
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