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

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Environmental stresses, such as cold, heat, salinity, and drought, induce ethylene production and oxidative stress and cause damage in plants. On the other hand, studies have shown that salicylic acid (SA) induced resistance to environmental stresses in plants. In this research, the effects of ethylene on chlorophyll (Chl), carotenoid (Car), anthocyanin, flavonoids, ascorbic acid, dehydroascorbic acid, total ascorbate, lipid peroxidation, and ethylene production in leaves of canola pretreated with SA were studied. The plants were grown in pots until they have four leaves. Leaves were sprayed for two days with three different concentrations of SA (0, 0.5, and 1 mM). The plants were treated for three days with three concentrations of ethylene (0, 50, and 100 ppm). At the end of the ethylene treatments, all examined parameters were measured. The results showed that the ethylene treatments induced lipid peroxidation, while SA mitigated this effect. The ethylene treatment lowered significantly Chl and Car contents and anthocyanin accumulation, but SA alleviated these effects. SA induced an increase in ascorbic acid content in canola plants after the ethylene treatments. Therefore, we concluded that SA played an important role in the alleviation of damages caused by stress conditions.