Saponins are a large group of secondary metabolites occurring in significant amounts in many plant species. However, the saponin content of plants is variable and it can be influenced by the surrounding environment. The local geoclimate, seasonal changes, external conditions such as light, temperature, humidity and soil fertility, as well as cultivation techniques, affect both the quantitative amount and qualitative composition of saponins. Such variation substantially impacts on the quality and properties of wild and cultivated plants exploited for pharmaceutical, nutritional and industrial applications. This review summarizes the available data on the effects of abiotic environmental factors on saponin level in plants, especially those of considerable economic importance, highlighting current problems such as the reduction in natural plant resources, over-exploitation and destruction of wild habitats, climate shifts as well as the consequences of the growing demand for plantderived medicinal and industrial products. The need for a theoretical basis for a reasonable harvest, attempts at the domestication of wild plant species and the development of new agricultural technologies allowing high production under optimized conditions are also discussed.

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A method based on high-performance liquid chromatography coupled with diode array detection and electrospray ionization mass spectrometry (HPLC-DAD-ESI-MS) following fractionation by chromatography on a Sephadex LH-20 column has been developed to determine the phenolic composition of fruit of Eucalyptus globulus growing in Algeria. The presence of 18 gallotannins, 26 ellagitannins, and 2 flavonols was established. Tentative identification is provided for these compounds on the basis of UV-visible spectra and mass spectrometry data. Most compounds described in this study have not previously detected in fruit of E. globulus. Moreover, this is the first report of methyl digalloyl diglucose, 3,3'-O-dimethylellagic acid 4-O-β-glucopyranoside, ellagic acid hexose, methyl ellagic acid pentose, methyltetragalloylglucose, and valoneic acid isomers (sanguisorbic, flavogallic acid dilactone) in the genus Eucalyptus. Quantitatively, ellagic acid and its derivatives, including ellagitannins, are largely predominant.

Saponins occur constitutively in many plant species as part of their defense system. However, saponin content in plants seems to be dynamic, responding to many external factors including various biotic stimuli connected to herbivory attack and pathogenic infection, as well as involved in plant mutualistic symbioses with rhizobial bacteria and mycorrhizal fungi. Thus, not only saponins influence the living organisms interacting with plants, but in turn, all these interactions can impact the plant saponin content. According to their constitutive occurrence in plants, saponins are regarded mainly as phytoanticipins. Nevertheless, some presented data clearly point out to induced biosynthesis of saponins, especially in plant response to insect herbivory or inoculation with root symbionts, while the best studied examples of interactions between plants and their microbial pathogens show rather qualitative change of saponin composition based on chemical modifications of preformed, pre-infectional precursors. Simultaneously, despite evident inducibility of saponin production in plant cell cultures, the possible role of these compounds as phytoalexins synthesized in intact plants after pathogen infection is still not well documented. Some practical patterns and ecological consequences of biotic factors influencing saponin content in plants are briefly highlighted, with the special attention paid to microbial inoculants applied for optimisation of saponin synthesis in cultivated medicinal plants.