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This study investigated the effect of seaweed extract (SWE) sprays obtained from Ulva rigida on wheat plants (Triticum durum L., variety Karim) grown under salt stress conditions for six weeks. Three levels of NaCl (0, 34.22, 68.44 mM) and four different concentrations (0, 12.5, 25 and 50%) of Ulva rigida as a water extract were applied. The obtained results indicated that seaweed treated plants showed higher ability to tolerate salt stress (34.22 or 68.44 mM of NaCl) by a significant (p < 0.05) increase of plant growth and the photosynthetic pigment contents, compared to those of control (non-treated plants). Furthermore, there was a significant improvement in antioxidant enzyme activity, such as superoxide dismutase (SOD), isocitrate dehydrogenase (ICDH), glutathione peroxidase (GPx), glutathione reductase (GR) activities in the stressed plants, especially in those treated with 12.5% of SWE. Overall, our results suggest that the application of the Ulva rigida water extract could be used as a promising plant growth biostimulant for treating wheat plants under salinity stress.

The present investigation examined the effect of a seaweed extract (SWE) of Ulva rigida applied at different concentrations: 25, 50, and 75 % to sage plant (Salvia officinalis L.) subjected to drought stress tolerance. Three watering treatments, without stress (WS), moderate water deficit (MWS), and severe water deficit (SWD) corresponding respectively to 82, 18, and 7 % field capacity (FC), were used to understand the metabolic and physiological changes of Salvia plant during water deficit. SWE application enhanced vegetative growth in sage plants under drought stress conditions. The shoot length, total leaf area, and number were significantly reduced under water stress treatment. All SWE concentrations enhanced these growth parameters under water deficit. Maximal shoot number was observed with application of 25 % U. rigida extract under MWD that resulted in increases of 40 % compared to the control plants. Water stress increased glycine betaine (GB) content, that was significantly reduced by all concentration of SWE applied. The maximum reduction of GB was observed with the 50 % SWE treatment. The lipid peroxidation was less pronounced in droughtstressed plants treated with SWE. The lowest content of malondialdehyde (MDA) was in non-stressed plants and 50 % SWE treatment. The total phenolic content was reduced in plants with increased water deficit intensity (30 % reduction of TFC under SWD) but improved by all concentrations of SWE applied. Drought stress increased the superoxide dismutase (SOD) activities when compared to control. There was a significant enhancement of SOD activity and ascorbate peroxydase (APX) activity when sage plants were treated by SWE under deficit water. The beneficial effect of SWE varied with extract concentrations applied. No significant effect was observed with treatment of SWE. Results indicated that seaweed extract of U. rigida application to medicinal plant S. officinalis under water resulted in amelioration of drought stress and helped in enhancement of antioxidant potential and drought tolerance.

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