Osmoprotectants and Nonenzymatic Antioxidants in Halophytes

Abstract

Salt tolerance is a complex phenomenon leading to ionic imbalance, osmotic stress, and excessive generation of reactive oxygen species (ROS). Halophytes developed a range of adaptations to tolerate disturbances in their redox homeostasis caused by high salinity alone or by its combination with other stresses. Osmoprotectants are universal molecules whose chemical structure allows them for making efficient osmotic adjustments and exerting antioxidant activity. Combining these two abilities, they become effective molecules that prevent membrane injury and stabilize proteins/enzymes under high concentrations of salts or other harmful solutes. Components of antioxidant systems together with some osmoprotectants act as ROS regulating networks. Selected compatible solutes (carbohydrates, polyols, amino acids, betaines, polyamines, phenols) (i) allow for balancing ROS level and redox status, (ii) are involved in ROSdependent signaling pathways, and (iii) activate the osmotic response network under salt stress. Osmolytes are also sources of carbon, nitrogen, sulfur, and energy for cells. Through the interaction with other biocompounds and/or their involvement in different metabolic pathways/metabolic loops, they can modulate metabolic homeostasis, especially under environmental stresses, and thus affect plant salt tolerance.

Evaluation and Comparison of the Antimelanogenic Properties of Different Solvent Fractionated Cnidium japonicum Extracts in B16F10 Murine Melanoma Cells

“…Some studies have indicated that antioxidant natural products exhibit pigmentation-delaying properties by scavenging oxygen and nitrogen species as well as reducing intermediate quinone derivatives that play roles in the oxidative polymerization steps of melanogenesis ( Nahhas et al, 2019 ; Xing et al, 2022 ). In this context, halophytes are known for their diverse and abundant content of antioxidants ( Surówka and Hura, 2020 ). Moreover, UV radiation was suggested to increase the α-MSH-mediated tyrosinase production using free radicals whose levels were elevated during prolonged exposure to UV ( Nahhas et al, 2019 ).…”

Similar Responses of Relatively Salt-Tolerant Plants to Na and K during Chloride Salinity: Comparison of Growth, Water Content and Ion Accumulation

“…However, the majority of halophytes are thought to represent salt accumulators, but even for these species, the ion concentration in the mesophyll tissues of photosynthetically active organs can be diminished by means of salt secretion to the leaf surface (recretohalophytes), an increase in tissue water content (succulent halophytes) and the accumulation of salts in older leaves [ 4 ]. Salt-accumulating halophytes use a cellular compartmentation strategy, accumulating salts in vacuoles, further solving a problem of proper osmotic adjustment [ 15 ]. The control of electrolytical activity in plant tissues due to salinity has been much less often considered, but it seems that coastal species from salt-affected habitats show different strategies, regulating leaf tissue electrical conductivity (EC) by changes in either K + or Na + concentration, but some species relatively tightly control the EC level by concomitant changes in both K + and Na + concentration [ 16 ].…”