Balance of Δ5-and Δ7-sterols and stanols in halophytes in connection with salinity tolerance

Stigmasterol: An Enigmatic Plant Stress Sterol with Versatile Functions

Sterols play important structural and regulatory roles in numerous intracellular processes. Unlike animals, plants contain a distinctive and diverse variety of sterols. Recently, information has emerged showing that stigmasterol is a "stress sterol". Stigmasterol is synthesized via the mevalonate biosynthesis pathway and has structural similarity to β-sitosterol but differs in the presence of a trans-oriented double bond in the side chain. In plants, the accumulation of stigmasterol has been observed in response to various stresses. However, the precise ways that stigmasterol is involved in the stress responses of plants remain unclear. This comprehensive review provides an update on the biology of stigmasterol, particularly the physicochemical properties of this ethylsterol, its biosynthesis, and its occurrence in higher plants and extremophilic organisms, e.g., mosses and lichens. Special emphasis is given to the evolutionary aspects of stigmasterol biosynthesis, particularly the variations in the gene structure of C22-sterol desaturase, which catalyzes the formation of stigmasterol from β-sitosterol, in a diversity of evolutionarily distant organisms. The roles of stigmasterol in the tolerance of plants to hostile environments and the prospects for its biomedical applications are also discussed. Taken together, the available data suggest that stigmasterol plays important roles in plant metabolism, although in some aspects, it remains an enigmatic compound.

Chemical and Biochemical Features of Spinasterol and Schottenol

Phytosterols, which are produced in plants, are structurally similar to cholesterol. Their basic structures consist of a cyclo pentano-perhydrophenanthrene nucleus composed of 3 hexane rings and of a pentane ring with an alkyl side chain. There are around more than 250 phytosterols and related compounds that have been identified in natural resources. Among them, spinasterol and schottenol, its dihydro analog, are often found in seeds, and consequently in seed oils, and in other botanical parts of some plant families such as Sapotaceae, Cactaceae, and Cucurbitaceae. Spinasterol and/or schottenol has been identified in dietary and cosmetic argan oil, milk thistle seed oil, nigella seed oil, and pumkin seed oil. These phytosterols that have several bioactive properties make them potentially attractive molecules in pharmacology. Their chemical and biochemical features are summarized and the analytical methods used to characterize and analyze these compounds are presented.

Antihyaluronidase and Antioxidant Potential of Atriplex sagittata Borkh. in Relation to Phenolic Compounds and Triterpene Saponins

The genus Atriplex provides species that are used as food and natural remedies. In this work, the levels of soluble phenolic acids (free and conjugated) and flavonoids in extracts from roots, stems, leaves and flowers of the unexplored Atriplex sagittata Borkh were investigated by LC-ESI-MS/MS, together with their antioxidant and antihyaluronidase activity. Phenolic acids were present in all parts of A. sagittata; and were most abundant in the leaves (225.24 μg/g dw.), whereas the highest content of flavonoids were found in the flowers (242.71 μg/g dw.). The most common phenolics were 4-hydroxybenzoic and salicylic acids, kaempferol-3-glucoside-7-rhamnoside, kaempferol-3-rutinoside and the rare narcissoside, which was present in almost all morphotic parts. The stem extract had the highest antioxidant activity and total phenolic content (611.86 mg/100 g dw.), whereas flower extract exerted the most potent antihyaluronidase effect (IC₅₀ = 84.67 µg/mL; control-quercetin: IC₅₀ = 514.28 μg/mL). Phytochemical analysis of the flower extract led to the isolation of two triterpene saponins that were shown to be strong hyaluronidase inhibitors (IC₅₀ = 33.77 and 168.15 µg/mL; control-escin: IC₅₀ = 307.38 µg/mL). This is the first report on the presence of phenolics and saponins in A. sagittata. The results suggest that both groups of metabolites may contribute to the overall activity of this plant species.