Background: Salicylic acid (SA) acts as a potential non-enzymatic antioxidant and a plant growth regulator, which plays a major role in regulating various plant physiological mechanisms. The effects of salicylic acid (SA; 0.05 mM) on physiological parameters, antioxidative capacity and phenolic metabolism, lignin, alkaloid accumulation in salt stressed Catharanthus roseus were investigated. Materials and Methods: Catharanthus roseus seeds were grown for two months in a glass house at 27-30 0 C in sunlight, and then divided into four different groups and transplanted with each group with the following solutions for one month: group I (non-saline control), group II, 100 mM NaCl, group III, 0.05 mM SA, group IV, 100 mM NaCl+0.05 mM SA and to determine the physiological parameters (DW, FW, WC), chlorophyll contents, carotenoid contents, lipid peroxidation, phenolics, lignin, alkaloid and enzymatic assays in each leaf pairs and roots. Results: SA exhibited growth-promoting property, which correlated with the increase of dry weight, water content, photosynthetic pigments and soluble proteins. SA has additive effect on the significant increase in phenylalanine ammonia-lyase (PAL) activity, which is followed by an increase in total soluble phenolics and lignin contents in all leaf pairs and root of C. roseus. SA enhances malondialdehyde content in all leaf pairs and root. The antioxidant enzymes (catalase, glutathione reductase, glutathione-S-tranferase, superoxide dismutase, peroxidase) as well as alkaloid accumulation increased in all treatments over that of non-saline control but the magnitude of increase was found more in root. Further, the magnitude of increase of alkaloid accumulation was significantly higher in 100 mM NaCl, but highly significant was found in presence of 0.05 mM SA and intermediate in presence of both 0.05 mM SA+100 mM NaCl. Conclusion:We concluded that applied SA to salt stress, antioxidant and phenolic metabolism, and alkaloid accumulation were significantly altered and the extent of alteration varied between the SA and salt stress.
The effect of exogenously applied salicylic acid (SA, 0.1 mM) on plant growth parameters, compatible solutes (proline, glycinebetaine) accumulation and on proline metabolism, in leaves and roots of Chamomile recutita plants grown in saline and non-saline control was investigated. Exogenously applied SA resulted increased plant growth significantly both in saline and non-saline conditions. The magnitude of increase in free proline accumulation was significantly increased in presence of NaCl but highly significant was found with the addition of SA to NaCl in leaves. Proline was found ≈5.3 folds increased in leaves and ≈1.3 folds only in root in presence of both treatments NaCl+SA with age of plant growth over that of non-saline control. Leaves tissue always maintained higher level of free proline contents than the roots. Anabolic enzymes such as pyrroline-5carboxylate reductase and γ-glutamyl kinase activities increased in all three treatments than the non-saline control and the magnitude of increase was found more pronounced in presence of both treatments than the others. In other way catabolic enzyme, proline oxidase activity was inhibited in all treatments. Nevertheless, the reduction in the activity was more in presence of both treatments than the others. Therefore, during the exogenously applied SA to salt stress, proline metabolism was significantly altered and the extent of alteration varied between the SA and salt stress, leading to the maintenance of the turgor by accumulating higher levels of free proline accumulation in C. recutita, supporting its protection from salt stress. Further, with addition of SA to salt of C. recutita was evident from the higher level of glycinebetaine (GB) compared with non-saline control or/others treatments. The enhanced activities of P-5-CR & γ-glutamyl kinase, and proline content in response to NaCl and/or SA treatment, whereas their interaction had an additive/cumulative effect. Hence, SA could be used as a potential growth regulator to improve plant salt stress tolerance. It was, therefore, concluded that SA ameliorated the stress generated by salt through the alleviated proline metabolic pathway/system.
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