Exogenous SA Applications Alleviate Salinity Stress via Physiological and Biochemical changes in St John’s Wort Plants

Abstract

The plant St. John’s wort contains high levels of melatonin, an important biochemical that has both beneficial and adverse effects on stress. Therefore, a method for increasing melatonin levels in plants without adversely affecting their growth is economically important. In this study, we investigated the regulation of melatonin levels in St. John’s wort by exposing samples to salinity stress (150 mM) and salicylic acid (0.25 mM) to augment stress tolerance. The results indicated that salinity stress significantly reduced the plant chlorophyll content and damaged the photosystem, plant growth and development. Additionally, these were reconfirmed with biochemical indicators; the levels of abscisic acid (ABA) and proline were increased and the activities of antioxidants were reduced. However, a significant increase was found in melatonin content under salinity stress through upregulation in the relative expression of tryptophan decarboxylase (TDC), tryptamine 5-hydroxylase (T5H), serotonin N-acetyltransferase (SNAT), and N-acetylserotonin methyltransferase (ASMT). The salicylic acid (SA) treatment considerably improved their photosynthetic activity, the maximum photochemical quantum yield (133%), the potential activity of PSⅡ (294%), and the performance index of electron flux to the final PS I electron acceptors (2.4%). On the other hand, SA application reduced ABA levels (32%); enhanced the activity of antioxidant enzymes, such as superoxide dismutase (SOD) (15.4%) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) (120%); and increased polyphenol (6.4%) and flavonoid (75.4%) levels in salinity-stressed St. John’s wort plants. Similarly, SA application under NaCl stress significantly modulated the melatonin content in terms of ion balance; the level of melatonin was reduced after SA application on salt-treated seedlings but noticeably higher than on only SA-treated and non-treated seedlings. Moreover, the proline content was reduced considerably and growth parameters, such as plant biomass, shoot length, and chlorophyll content, were enhanced following treatment of salinity-stressed St. John’s wort plants with salicylic acid. These findings demonstrate the beneficial impact of salt stress in terms of a cost-effective approach to extract melatonin in larger quantities from St. John’s wort. They also suggest the efficiency of salicylic acid in alleviating stress tolerance and promoting growth of St. John’s wort plants.

Influence of N-Acetylglucosamine and Melatonin Interaction in Modeling the Photosynthetic Component and Metabolomics of Cucumber under Salinity Stress

“…The interrelationships of abscisic acid and proline content in water balance and electrolytic leakage to regulate stomatal conductance have been widely accepted by several researchers [ 29 ]. ABA plays a crucial role in the sustenance and degradation of proline synthesis, particularly in water-deficient conditions where proline directly regulates the guard cell movement, stomatal conductance, and ultimately transpiration rate triggered by ABA [ 30 ].…”

“…Since GlcNAc exerts a positive impact on the cucumber plant under salt stress, the combination of GlcNAc/Mel could be one effective method to combat abiotic stresses. Additionally, NaCl stress although exerted negative effects could be an efficient elicitor of melatonin synthesis, as observed in grapevine leaves and St. John’s wort [ 29 , 56 ]. This could potentially be employed in the melatonin extraction process for industrial purposes.…”

Novel melatonin‐producing Bacillus safensis EH143 mitigates salt and cadmium stress in soybean

“…Dried samples were re-suspended in 400 μl of 1x stabilizer and quantified in accordance with the kit's protocol. The optical density was measured at 450 nm using a spectrophotometer (Multiskan GO, Thermo Fischer Scientific, USA) as described by Kwon et al 44 T A B L E 1 Details of the EH143, NaCl, and Cd treatments to soybean plants.…”

Dynamics of Humic Acid, Silicon, and Biochar under Heavy Metal, Drought, and Salinity with Special Reference to Phytohormones, Antioxidants, and Melatonin Synthesis in Rice

“…The method described by Kwon et al [75] was followed to detect and quantify the melatonin content in the rice shoots using a commercial Melatonin ELISA Kit (Enzo Life Sciences, Inc., Farmingdale, NY, USA). A lyophilized ground-up sample was homogenized with 1 × stabilizer and cold ethyl acetate (125 µL and 750 µL, respectively), centrifuged, and the obtained layer was separated and air-dried using N 2 .…”