Influence of Light Conditions and Medium Composition on Morphophysiological Characteristics of Stevia rebaudiana Bertoni In Vitro and In Vivo

The Impact of LED Light Spectra on the Growth, Yield, Physiology, and Sweetness Compound of Stevia rebaudiana

This study investigated the effects of several light spectra on Stevia rebaudiana, analysing growth parameters, yield, and physiological responses within a controlled-environment agriculture (CEA) system. The experimental design involved different light treatments, including specific combinations of blue (435 nm and 450 nm), red (663 nm), and ultraviolet (UV) wavelengths (365 nm), to determine their impact on morphological development and biochemical properties, particularly focusing on the production of the sweetening compounds stevioside and rebaudioside A. Stevia rebaudiana plants cultivated from cuttings sourced from a reputable UK nursery (Gardener's Dream Ltd., Glasgow, UK) were subjected to these spectral treatments over a period of five weeks under vertical farming conditions. Physiological measurements, such as chlorophyll fluorescence (Fv/Fm), stomatal conductance, and leaf temperature, were recorded, alongside growth metrics (plant height, leaf area, and biomass). This study also incorporated high-performance liquid chromatography (HPLC) to quantitatively analyse the influence of the light treatments on the sweetener concentration. The results demonstrated that targeted LED spectra, particularly those that include UV light and blue light (435 nm), significantly nhanced both the quantitative and qualitative attributes of stevia growth, indicating that strategic light management can markedly improve the nutritional and commercial yields of Stevia rebaudiana. This research contributes to the optimisation of light conditions in vertical farming systems, aiming to enhance agricultural efficiency and reduce the reliance on imported stevia by maximising local production capabilities.

LED light improves shoot multiplication, steviol glycosides and phenolic compounds biosynthesis in Stevia rebaudiana Bertoni in vitro culture

Light-emitting diode (LED) lamps are efficient elicitors of secondary metabolites. To investigate the influence of LED light on steviol glycosides (SGs) and phenolic compounds biosynthesis, stevia shoots were cultured under the following LED lights: white-WL, blue-B, red-R, 70% red and 30% blue-RB, 50% UV, 35% red and 15% blue-RBUV, 50% green, 35% red and 15% blue-RBG, 50% yellow, 35% red and 15% blue-RBY, 50% far-red, 35% red and 15% blue-RBFR and white fluorescent light (WFl, control). RBG light stimulated shoots' biomass production. RBFR had a beneficial impact on stevioside biosynthesis (1.62 mg/g dry weight, DW), while RBUV favoured the production of rebaudioside A (3.15 mg/g DW). Neochlorogenic, chlorogenic, caffeic, 4-feruloylquinic, isochlorogenic A, rosmarinic acids and the flavonoid quercitrin were identified in the obtained material. A stimulatory effect of RBFR and RBUV on the biosynthesis of phenolic compounds was noted. LED light also influenced stomata appearance, stomata density, photosynthetic pigments, soluble sugar content and antioxidant enzyme activities in stevia shoots. This is the first report to provide evidence of the stimulating effect of LED light on biomass yield, SGs production and phenolic compounds in stevia shoot cultures.

Influence of Abiotic and Biotic Elicitors on Organogenesis, Biomass Accumulation, and Production of Key Secondary Metabolites in Asteraceae Plants

The medicinal plants of the Asteraceae family are a valuable source of bioactive secondary metabolites, including polyphenols, phenolic acids, flavonoids, acetylenes, sesquiterpene lactones, triterpenes, etc. Under stressful conditions, the plants develop these secondary substances to carry out physiological tasks in plant cells. Secondary Asteraceae metabolites that are of the greatest interest to consumers are artemisinin (an anti-malarial drug from Artemisia annua L.-sweet wormwood), steviol glycosides (an intense sweetener from Stevia rebaudiana Bert.-stevia), caffeic acid derivatives (with a broad spectrum of biological activities synthesized from Echinacea purpurea (L.) Moench-echinacea and Cichorium intybus L.-chicory), helenalin and dihydrohelenalin (anti-inflammatory drug from Arnica montana L.-mountain arnica), parthenolide ("medieval aspirin" from Tanacetum parthenium (L.) Sch.Bip.-feverfew), and silymarin (liver-protective medicine from Silybum marianum (L.) Gaertn.-milk thistle). The necessity to enhance secondary metabolite synthesis has arisen due to the widespread use of these metabolites in numerous industrial sectors. Elicitation is an effective strategy to enhance the production of secondary metabolites in in vitro cultures. Suitable technological platforms for the production of phytochemicals are cell suspension, shoots, and hairy root cultures. Numerous reports describe an enhanced accumulation of desired metabolites after the application of various abiotic and biotic elicitors. Elicitors induce transcriptional changes in biosynthetic genes, leading to the metabolic reprogramming of secondary metabolism and clarifying the mechanism of the synthesis of bioactive compounds. This review summarizes biotechnological investigations concerning the biosynthesis of medicinally essential metabolites in plants of the Asteraceae family after various elicitor treatments.

In Vitro Multiplication and Rooting of Plum Rootstock 'Saint Julien' (Prunus domestica subsp. insititia) under Fluorescent Light and Different LED Spectra

In recent years, light emitting diodes (LEDs), due to their low energy consumption, low heat emission and specific wavelength irradiation, have become an alternative to fluorescent lamps (FLs) in plant tissue culture. The aim of this study was to investigate the effects of various LED light sources on the in vitro growth and rooting of plum rootstock Saint Julien (Prunus domestica subsp. insititia). The test plantlets were cultivated under a Philips GreenPower LEDs research module illumination system with four spectral regions: white (W), red (R), blue (B) and mixed (W:R:B:far-red = 1:1:1:1). The control plantlets were cultivated under fluorescent lamps (FL) and the photosynthetic photon flux density (PPFD) of all treatments was set at 87 ± 7.5 μmol m^-2 s^-1. The effect of light source on the selected physiological, biochemical and growth parameters of plantlets was monitored. Additionally, microscopic observations of leaf anatomy, leaf morphometric parameters and stomata characteristics were carried out. The results showed that the multiplication index (MI) varied from 8.3 (B) to 16.3 (R). The MI of plantlets grown under mixed light (WBR) was 9, lower compared to the control (FL) and white light (W), being 12.7 and 10.7, respectively. In addition, a mixed light (WBR) favored plantlets' stem growth and biomass accumulation at the multiplication stage. Considering these three indicators, we could conclude that under the mixed light, the microplants were of better quality and therefore mixed light (WBR) was more suitable during the multiplication phase. A reduction in both net photosynthesis rate and stomatal conductance in the leaves of plants grown under B were observed. The quantum yield (Yield = F_V/F_M), which represents the potential photochemical activity of PS II, ranged from 0.805 to 0.831 and corresponded to the typical photochemical activity (0.750-0.830) in the leaves of unstressed healthy plants. The red light had a beneficial effect on the rooting of plum plants; the rooting was over 98%, significantly higher than for the control (FL, 68%) and the mixed light (WBR, 19%). In conclusion, the mixed light (WBR) turned out to be the best choice during the multiplication phase and the red LED light was more suitable during the rooting stage.

Effects of Different Elicitors on Micropropagation, Biomass and Secondary Metabolite Production of Stevia rebaudiana Bertoni-A Review

Stevia rebaudiana Bertoni is a valuable plant whose products are increasingly used in medicine, pharmacy and the food industry. This necessitates the use of biotechnological approaches for its mass propagation. Establishing optimal conditions for in vitro cultivation is essential for obtaining high biomass and secondary metabolites production. A large number of articles considering the role of plant growth regulators and other additives in the culture medium in the growth and development of Stevia are available in the literature. However, there are no summarized data about the use of nanoparticles in Stevia tissue cultures. Therefore, this review also includes the research conducted so far on the effect of nanoparticles on Stevia micropropagation. Furthermore, the influence of different elicitors on secondary metabolite production and antioxidant activity of in vitro-cultivated Stevia plants have been discussed. By referring to the collected literature, we concluded that biotechnological approaches applied to S. rebaudiana cultivation might improve the agronomic traits of plants and steviol glycosides production.

Influence of Mineral Treatment, Plant Growth Regulators and Artificial Light on the Growth of Jewel Sweet Potato (Ipomoea batatas Lam. cv. Jewel) In Vitro

Sweet potato (Ipomoea batatas (L.) Lam), a member of the bindweed family (Convolvulaceae Juss.), is well known for its food, medicinal, and industrial values. It is estimated that more than 7000 sweet potato cultivars have been bred to date. Jewel sweet potato (I. batatas Lam cv. Jewel) is one of the most popular cultivars of sweet potato grown today because of its high nutritional value, delicious taste, and is suitable for all processing methods. However, little is known about the micropropagation of jewel sweet potato. The purpose of this paper was to study the effect of three important factors, including culture medium, plant growth regulators (PGRs), and artificial light sources, on the induction, proliferation, and growth of in vitro I. batatas 'Jewel' shoots obtained from the axillary bud and shoot tip explants. The different Murashige and Skoog (MS) salt levels (33%, 50%, 100%, and 150%) were used to study the influence of mineral treatment. To assess the influence of PGRs, we used 0.5 mg/L indole-3-acetic acid (IAA) combined with various cytokinins, including 0.5-2.0 mg/L 6-benzylaminopurine (BAP), 0.5-2.0 mg/L kinetin (Kn), and 0.1-1.0 mg/L thidiazuron (TDZ). On the other hand, the in vitro shoots were cultivated in a light room with different lighting conditions. Three lighting treatments (differences in the ratio between the red (R) and blue (B) spectra) were used. Research results have shown that the medium containing 50% MS salt concentration supplemented with 0.5 mg/L BAP or 0.5 mg/L Kn combined with 0.5 mg/L IAA was the most suitable for induction, proliferation, and growth of in vitro jewel sweet potato shoots. On the other hand, stem pieces bearing the axillary buds' explants were determined to be suitable for the shoot induction. Using artificial light with different blue/red ratios also had a significant effect on the growth of explants and stimulates shoot or root formation.

Influence of Plant Growth Regulators and Artificial Light on the Growth and Accumulation of Inulin of Dedifferentiated Chicory (Cichorium intybus L.) Callus Cells

Chicory (Chicorium intybus L.) is a perennial herb of the family Asteraceae, widely distributed in Asia and Europe, commonly used industrially as a raw material for extracting inulin because of a high content of inulin and biologically active compounds. Light conditions and plant growth regulators (PGRs) are two of many factors that affect the growth and inulin content of chicory callus. The aim of this work is to study the effect of PGRs and light conditions on proliferation and accumulation of inulin of chicory callus in vitro. In this study, we used semi-solid MS medium supplemented with different auxins (including Indole-3-acetic acid (IAA), naphthylacetic acid (NAA), and 2,4-dichlorophenoxyacetic acid (2,4-D)) at a concentration of 5.5−9.5 mg/L in combination with 2.0 mg/L 6 benzylaminopurine (BA) to determine induction and proliferation of callus. The increasing value of callus fresh weight was used to assess the growth of the callus in treatments. The results showed that a steady increase in callus fresh weight and inulin content in callus cells was obtained when they were cultured on MS medium supplemented with a combination of 2.0 mg/L BA with 7.5 mg/L IAA in lighting conditions with radiation equalized by the flux density of photosynthetic photons and ratios of radiation levels in the region of FR—far red > R—red. Increasing demand for organic inulin sources in production practice can be met by our finding.

Flavonoid Accumulation in an Aseptic Culture of Summer Savory (Satureja hortensis L.)

Summer savory (Satureja hortensis L.) is a medicinal and aromatic plant of the Lamiaceae family, a source of valuable secondary metabolites (monoterpenoids, rosmarinic acid, flavonoids). For this paper, flavonoid accumulation in an aseptic culture of summer savory was determined by using a colorimetric method. The organ specificity of flavonoid accumulation in aseptic plants was revealed: In leaves (8.35 ± 0.17 mg/g FW), flower buds (7.55 ± 0.29 mg/g FW), and calyx (5.27 ± 0.28 mg/g FW), flavonoids accumulated in significantly higher amounts than in stems (1.50 ± 0.22 mg/g FW) and corolla (0.78 ± 0.12 mg/g FW). We found that primary callus tissue formed from cotyledon and hypocotyl explants retains the ability to synthesize flavonoids at deficient levels (0.50 ± 0.09 mg/g FW and 0.44 ± 0.11 mg/g FW, respectively), that remained stable throughout six subcultures. Placing the callus tissue in monochrome lighting conditions with blue, green, and red light-emitting diode (LED) lamps leads to morphological changes in the tissue and decreased flavonoid accumulation compared to fluorescent lamps.

Effects of Light Spectral Quality on Photosynthetic Activity, Biomass Production, and Carbon Isotope Fractionation in Lettuce, Lactuca sativa L., Plants

The optimization of plant-specific LED lighting protocols for indoor plant growing systems needs both basic and applied research. Experiments with lettuce, Lactuca sativa L., plants using artificial lighting based on narrow-band LEDs were carried out in a controlled environment. We investigated plant responses to the exclusion of certain spectral ranges of light in the region of photosynthetically active radiation (PAR); in comparison, the responses to quasimonochromatic radiation in the red and blue regions were studied separately. The data on plant phenotyping, photosynthetic activity determination, and PAM fluorometry, indicating plant functional activity and stress responses to anomalous light environments, are presented. The study on carbon isotopic composition of photoassimilates in the diel cycle made it possible to characterize the balance of carboxylation and photorespiration processes in the leaves, using a previously developed oscillatory model of photosynthesis. Thus, the share of plant photorespiration (related to plant biomass enrichment with ¹³C) increased in response to red-light action, while blue light accelerated carboxylation (related to ¹²C enrichment). Blue light also reduced water use efficiency. These data are supported by the observations from the light environments missing distinct PAR spectrum regions. The fact that light of different wavelengths affects the isotopic composition of total carbon allowed us to elucidate the nature of its action on the organization of plant metabolism.

Effect of light intensity on steviol glycosides production in leaves of Stevia rebaudiana plants

Stevia rebaudiana leaf extracts contain stevioside and rebaudioside A, two steviol glycosides (SGs) used as natural sweeteners because of their non-toxic, thermally stable and non-caloric properties. Indeed, leaf extracts can be up to 300 times sweeter than sucrose. Stevioside and rebaudioside A have organoleptic differences, the first one having an undesirable bitterness and the second one a higher sweetener capacity. Selection of the S. rebaudiana varieties and the best environmental conditions that elicit higher SGs content and the appropriate composition is an important goal. In this study we quantified and compared the amount of stevioside and rebaudioside A in two of the most used S. rebaudiana cultivars, Morita II and Criolla. Our results show a strong differential ratio of stevioside and rebaudioside A accumulated in the leaf between these cultivars. The Criolla cultivar showed about 3 times more stevioside per mg of dry weight than Morita II, whereas the Morita II accumulated almost 10 times more rebaudioside A than that produced in Criolla. We observed an enhanced expression in Morita II of three genes (SrKA13H, SrUGT74G1 and SrUGT76G1) known to encode three enzymes that participate in SGs biosynthesis, likely contributing to the differences in the stevioside and rebaudioside A accumulation. Not only genetic variation can affect SGs composition, but also environmental factors and crop management. Numerous studies have shown that the light regime in which S. rebaudiana cultivars grow can affect SGs accumulation. However, the optimal light regime to increase total SGs content is currently controversial. By applying various light intensities, we detected an increase of expression of these three biosynthetic genes at higher light intensity, accompanied by higher levels of stevioside and rebaudioside A, demonstrating that light intensity influences the synthesis of SGs.

Effects of Light Spectral Quality on the Micropropagated Raspberry Plants during Ex Vitro Adaptation

This work focuses on developing light environments for the effective regulation of morphogenesis and ex vitro conditions adaptation in micropropagated raspberry plants on the basis of photomorphogenetic control of physiological processes using light-emitting diodes (LEDs). In experiments with cloned plants growing ex vitro in stressful conditions during acclimation, the effects of optical radiation of various spectral combinations from different photosynthetically active radiation (PAR) spectral regions were studied. The data on the plant development and state of the photosynthetic apparatus, features of photosynthetic gas exchange and transpiration, accumulation of photosynthetic pigments, light curves of photosynthesis, and data on growth processes in light modes using combined quasimonochromatic radiation (either mixture of red, green, and blue light or red, far-red, and blue light) with various ratio of the distinct spectral regions were obtained. Photosynthetic apparatus functional activity under different light conditions was studied with chlorophyll fluorescence determination, and plant stress responses to growing under artificial spectral light conditions were characterized. The experiments were accompanied by detailed plant phenotyping at the structural and functional levels. Plant acclimation and photosynthetic improvements in response to added far-red and green light wavelengths to the main red-blue spectrum have been elucidated.