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Salicylic acid (SA) is known as an influential signal molecule in plant responses to environmental stresses. In this study, the effects of SA as a pre-treatment of psyllium (Plantago ovata) seeds on seedling growth, photosynthetic pigments, proteins and amino acids, and accumulation of soluble sugars and starch in response to salinity stress were investigated. Psyllium seeds were soaked with 0 and 500 μM SA for 24 h and sown in the research greenhouse of Iranshahr University in 2019, and the seedlings were exposed as a factorial design to 0, 25, 50, 100, 150 and 300 mM NaCl at 3-day intervals for 20 days. The results showed the seedling growth rate, photosynthetic pigments including chlorophylls and carotenoids, protein concentration as well as accumulation of soluble sugars and starch were severely reduced due to salinity stress. However, the accumulation of free amino acids and proline increased in response to salt stress. SA treatment improved the length of the shoot, increased the amount of pigments, decreased the amount of amino acids, and caused the accumulation of proteins and proline. In addition, an increase in the amount of nonreducing sugars and starch, which was associated with no change or decrease in the concentration of reducing sugars at high salinity levels, occurred in response to SA. These results show that priming the seeds with SA before sowing can increase the plant tolerance to salinity stress through the accumulation of non-reducing sugars and proline and thus maintain the turgor pressure of cells. [ABSTRACT FROM AUTHOR]

In the present study, effects of foliar application of 150 µM Jasmonic acid (JA), an endogenous plant growth regulator, on alleviation oxidative stress resulted from without (0 mM), low (50 mM), moderate (150 mM), and high (300 mM) NaCl in bitter melon (Momordica charantia) seedlings was investigated. High salt stress significantly decreased growth components including root length, leaf morphological properties, leaf water content, plant biomass and levels of pigments, soluble sugars, starch and proteins, but accumulated higher amounts of proline, free amino acids and the activities of ascorbate peroxidase (APX), catalase (CAT), polyphenol oxidase (PPO) and pyrogallol peroxidase (PPX). Exogenous JA treatment alone or combined with salt stress improved growth components with hyperaccumulation of soluble sugars, proteins, amino acids, proline and PPO activity, but was associated with a decrease in the activity of H2O2-decomposing enzymes. These results suggest that exogenous JA treatment can effectively raise salt stress tolerance of bitter melon seedlings through modifying allocation of carbon and nitrogen metabolism to adjust levels of metabolites and directing them to the growth processes. [ABSTRACT FROM AUTHOR]

Natural phenolic acids and their derivatives in plant extracts in addition to wide use in food industry, have also medicinal properties. In the present study, the antioxidant and antimicrobial activities of ethanol and water extracts of Periploca aphylla, Persian walnut and oleander leaves were evaluated using assays of 2,2-diphenyl-1-picrylhydrazyl radical-scavenging activity, hydrogen peroxide scavenging activity and ferric-reducing capacity. In addition, total phenolic compounds, total flavonoids and anthocyanins content of the extracts were determined. The plants extracts showed different levels of antioxidant properties in various assays. The ethanol extracts, which have the highest amount of total phenolics and flavonoids, showed the highest antioxidant and antimicrobial activities in all assays, compared with water extracts. The extracts of P. aphylla were found to have the highest antioxidant potential, followed by Persian walnut and oleander extracts. The highest antimicrobial activity was found for both ethanol and aqueous extracts of P. aphylla, which showed the greatest effect on Gram-positive bacteria. The results suggest that the leaves of these plants specifically P. aphylla can be considered as a new source of natural antioxidant. [ABSTRACT FROM AUTHOR]

The effect of propyl gallate (PG), a synthetic antioxidant, on antioxidant responses and salinity tolerance was investigated in the cells of the green microalga, Dunaliella bardawil. Algal suspensions grown at three salinity levels of 1, 2, and 3 M NaCl were incubated with 1 mM of PG. The number of cells was significantly lower in all PG-treated cells compared to untreated controls. Despite PG-induced cell death, the fresh weight of all PG-treated cells was considerably higher than controls. PG-treated cells had enhanced antioxidant capacity because of increased levels of Chlorophyll a, β-carotene, reduced ascorbate, protein, and enzymatic activities, but accumulated lower levels of malonyldialdehyde and hydrogen peroxide compared to untreated cells. The results suggest that PG acts as a signal molecule both directly by reducing of free radical oxidants and indirectly by augmenting ascorbate pool levels, β-carotene production, and antioxidant enzymes activity to boost the capacity of antioxidant systems and radical oxygen species scavenging. Therefore, induction of salt stress tolerance by PG in D. bardawil is associated with metabolic adjustments through activation or synthesis of both enzymatic and non-enzymatic molecules involved in antioxidant systems. [ABSTRACT FROM AUTHOR]