Steviol glycosides (SvGls) are plant secondary metabolites belonging to a class of chemical compounds known as diterpenes. SvGls have been discovered only in a few plant species, including in the ...leaves of
Stevia rebaudiana
Bertoni. Over the last few decades, SvGls have been extensively researched for their extraordinary sweetness. As a result, the nutritional and pharmacological benefits of these secondary metabolites have grown increasingly apparent. In the near future, SvGls may become a basic, low-calorie, and potent sweetener in the growing natural foods market, and a natural anti-diabetic remedy, a highly competitive alternative to commercially available synthetic drugs. Commercial cultivation of stevia plants and the technologies of SvGls extraction and purification from plant material have already been introduced in many countries. However, new conventional and biotechnological solutions are still being sought to increase the level of SvGls in plants. Since many aspects related to the biochemistry and metabolism of SvGls in vivo, as well as their relationship to the overall physiology of
S. rebaudiana
are not yet understood, there is also a great need for in-depth scientific research on this topic. Such research may have positive impact on optimization of the profile and SvGls concentration in plants and thus lead to obtaining desired yield. This research summarizes the latest approaches and developments in SvGls production.
Key points
• Steviol glycosides (SvGls) are found in nature in S. rebaudiana plants.
• They exhibit nutraceutical properties.
• This review provides an insight on different approaches to produce SvGls.
• The areas of research that still need to be explored have been identified.
The herbs of lemon balm, oregano, and peppermint were analysed immediately after harvest and after drying to determine their antioxidant activity and content of total phenolics,
l-ascorbic acid, and ...carotenoids. The strongest inhibition of linoleic acid (LA) peroxidation was found for fresh and dried oregano. For peppermint and lemon balm it was significantly lower and decreased after drying. The ability to scavenge the free radical DPPH (2,2-diphenyl-1-picrylhydrazyl) was very high in almost all tested samples, exceeding 90%. The three species tested had a very high content of total phenolics and drying of oregano and peppermint resulted in their considerable increase. The highest content of ascorbic acid was determined in fresh peppermint and lemon balm and carotenoid content was at a similar level in all the species tested. Drying caused great losses of these compounds.
Non-degradable polypropylene nonwovens are difficult to dispose and their utilization represents high economic costs. This study was conducted on lettuce cultivated during the spring and autumn ...seasons in the southern part of Poland to test biodegradable nonwovens as plant covers. Several nonwovens were developed from aliphatic-aromatic copolyesters (ACC), one without modifiers (SB48/11) and three with the addition of fatty acid dimers: two commercial variants (SB20/13, SB21/13) and one made from plant biomass (SB28/13). Nonwoven polypropylene (PP) fleece was included as a control cover. One week after covering with SB48/11, stomatal conductance (gs) increased in lettuce plants in parallel with higher transpiration rate (E) and sub-stomatal CO2 concentration (Ci) relative to the control, but differences in these parameters evened out in mature plants. In the spring, degradable covers with their higher mass per unit area, caused a decrease in marketable yield of lettuce compared to the control PP, resulting mainly from the deterioration of plant quality and lower mean weight per head. In the autumn season, yield was statistically not different between treatments. Yield of spring lettuces was 78% higher compared to the autumn cultivation period. Plants grown under SB20/13 had the lowest dry weight and L-ascorbic acid, while plants under SB21/13 had the highest dry weight and L-ascorbic acid content. Plants under SB28/13 had higher chlorophyll a content. Generally, no effect of covers was noted for carotenoid concentrations. The content of dry weight, L-ascorbic acid, and carotenoids were higher in plants harvested in spring, while no effects of crop season on chlorophyll level were observed. All tested biodegradable nonwovens are a potential substitute for standard polypropylene in autumn trials, but for spring covering unit weight of these materials should be reduced.
The growing of sage (Salvia officinalis L.) and balm (Melissa officinalis L.) in pots for the purpose of obtaining fresh culinary herbs was conducted during four terms from spring to autumn. The ...objective was to determine the possibility of using stem cuttings taken at different developmental stages of the mother plants and to compare this method of plant propagation with that based on seeds. The period of sage growth was shorter when it was raised from cuttings than from seeds. In the case of balm, the use of cuttings was more effective than generative propagation in the period from summer to autumn. In both species, the best results of rooting were achieved when cuttings were taken before plant flowering in spring and after flowering in August. The poorest balm rooting was recorded when taking cuttings at plant flowering, and at flowering and after flowering in July for sage.
•male and female gametophytogenesis in Stevia rebaudiana Bertoni have been visualized•high viability of mature pollen grains but weak pollen germination rate was found•difficulties in seeds ...development and their poor germination was stated•low level of GAs in favor of SGs is suggested as a cause of pollen recalcitrance
Seed germination in Stevia rebaudiana is poor and seedlings are difficult to achieve, thus the generative reproduction of this plant is limited. The aim of our studies was to investigate the stages of female and male gametophyte development along with pollen viability and pollen germination. Although our results showed the proper way of stevia male and female gametophyte development and a high viability of mature pollen grains, the lack of pollen tube formation followed by difficulties in seed development were still observed. We hypothesize that trouble with propagation of S. rebaudiana by seed might be caused by the unsuitable level of gibberellins (GAs) that are commonly recognized as signaling factors during the transition from the vegetative to the generative developmental phase. We found the decrease in the concentration of some GAs during plants flowering and we concluded that this might cause the inability of pollen tube germination. Moreover, S. rebaudiana plants exhibit a high concentration of steviol glycosides (SGs) that are synthesized in the biosynthetic pathway sharing some steps with the GAs formation. Therefore, the redirection of the metabolic pathway into secondary metabolites biosynthesis might be a reason for the failure in stevia pollen grains proper function.
•Stevia strains can be grown in temperate climate under the tunnel and in the field.•Differences between stevia strains resulted from differences in metabolic activity.•High photosynthetic efficiency ...is correlated with high steviol glycosides level.•Steviol glycosides might function in the protection of photosynthetic apparatus.
The objective of this study was to evaluate the development and the quality of leaves from several S. rebaudiana Bertoni strains cultivated under temperate climate conditions in the tunnel and in the open field in the relation to the photosynthetic activity. Investigated stevia strains differed significantly in terms of whole plant and leaf morphology, photosynthetic efficiency as well as in the content of steviol glycosides, and antioxidant capacity, independently of cultivation place. On the basis of several chlorophyll a fluorescence parameters analysis it was stated that plants of all examined strains, did not exhibit photosynthesis inhibition. The studies of the relationship between photosynthetic activity and the level of secondary metabolites indicated that the highest content of steviol glycosides and phenolic compounds had plants showing also the highest value of the energy fraction photochemically converted in PS II (YII), while the highest ratio of rebaudioside A to stevioside content corresponded with low amount of energy dissipated as a heat (YNPQ). This results might indicate that steviol glycosides play a role in the better adaptation to environmental conditions. Karyology and cytometric studies revealed that all investigated stevia strains were diploids without significant differences in 2C DNA amount. Therefore, observed diversity in the content of steviol glycosides and phenolic compounds between investigated S. rebaudiana strains was not the effect of polyploidization but probably resulted from the differences in the metabolic activity of the examined plants.
Herb and underground organs of dropwort have been used as medicinal raw materials. Decrease of natural resources of this species results in the necessity to introduce it into cultivation. In this ...study accumulation of biomass and phenolic compounds in underground organs of cultivated dropwort during two years of plant vegetation was evaluated. Underground organs were harvested at the end of the first year of plant vegetation and in the second year: at the beginning of vegetation, at the stage of blooming, and at the end of vegetation. Phenolics were determined by HPLC. At the end of the second year the weight of air-dry rhizomes with tuberous roots reached 188.3 g per plant and it was almost five times higher than in the first year. Underground organs of dropwort appeared to be a rich source of flavan-3-ols and gallic acid. There was no clear relation between the stage of plant development and accumulation of phenolics in these organs.
Polypropylene (PP) covers are used in radish (Raphanus sativus L. var. sativus) production to provide better microclimate for improving yield and quality, but disposing of non-degradable covers is ...difficult and expensive. In this work, nonwovens prepared from biodegradable polymers (aliphatic-aromatic copolyesters with and without fatty acid dimers: SB48/11, SB20/13, SB21/13, SB28/13) were tested in the field as substitutes for nonwoven PP. Minimum air temperature under biodegradable covers was higher by 0.6-0.8 degreesC than under nonwoven PP, but photosynthetically active radiation (PAR) transmission was lower by 4.1% (SB20/13) and 7.1% (SB21/13). We observed a decrease in marketable yield of plants covered with biodegradable fleeces by 1.01 to 2.90 kg m.sup.-2 (SB48/11 and SB28/13, respectively) in spring seasons, but similar yields to nonwoven PP were obtained in the autumn seasons. Dry weight, soluble sugars, L-ascorbic acid, pigments content in radish was dependent on a specific set of environmental conditions rather than on the type of cover. However, L-ascorbic acid content in the roots increased significantly by 6.4 and 2.9 mg 100 g.sup.-1 FW for SB48/11 and SB20/13 (in one trial), respectively, as compared to nonwoven PP. It is possible to use biodegradable nonwovens as floating covers for radish cultivated in seasons with temperature drops. Key words: Aliphatic-aromatic copolyesters, degradable nonwovens, PAR, Raphanus sativus, temperature, yield.
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