Effects of cerous nitrate on growth and tanshinone production in salvia miltiorrhiza hairy roots

Application of Hairy Root Culture for Bioactive Compounds Production in Medicinal Plants

Medicinal plants are rich sources of natural bioactive compounds used to treat many diseases. With the development of the health industry, the market demands for Chinese medicine have been rapidly increasing in recent years. However, over-utilization of herbal plants would cause serious ecological problems. Therefore, an effective approach should be developed to produce the pharmaceutically important natural drugs. Hairy root culture induced by Agrobacterium rhizogenes has been considered to be an effective tool to produce secondary metabolites that are originally biosynthesized in the roots or even in the aerial organs of mature plants. This review aims to summarize current progress on medicinal plant hairy root culture for bioactive compounds production. It presents the stimulating effects of various biotic and abiotic elicitors on the accumulation of secondary metabolites. Synergetic effects by combination of different elicitors or with other strategies are also included. Besides, the transgenic system has promising prospects to increase bioactive compounds content by introducing their biosynthetic or regulatory genes into medicinal plant hairy root. It offers great potential to further increase secondary metabolites yield by the integration of manipulating pathway genes with elicitors and other strategies. Then advances on two valuable pharmaceuticals production in the hairy root cultures are illustrated in detail. Finally, successful production of bioactive compounds by hairy root culture in bioreactors are introduced.

Primary and secondary metabolites produced in Salvia miltiorrhiza hairy roots by an endophytic fungal elicitor from Mucor fragilis

Salvia miltiorrhiza is one of the most commonly used medicinal materials in China. In recent years, the quality of S. miltiorrhiza has attracted much attention. Biotic and abiotic elicitors are widely used in cultivation to improve the quality of medicinal plants. We isolated an endophytic fungus, Mucor fragilis, from S. miltiorrhiza. We compared the effects of endophytic fungal elicitors with those of yeast extract together with silver ion, widely used together as effective elicitors, on S. miltiorrhiza hairy roots. Seventeen primary metabolites (amino acids and fatty acids) and five secondary metabolites (diterpenoids and phenolic acids) were analyzed after elicitor treatment. The mycelium extract promoted the accumulation of salvianolic acid B, rosmarinic acid, stearic acid, and oleic acid in S. miltiorrhiza hairy roots. Additionally, qPCR revealed that elicitors affect the accumulation of primary and secondary metabolites by regulating the expression of key genes (SmAACT, SmGGPPS, and SmPAL). This is the first detection of both the primary and secondary metabolites of S. miltiorrhiza hairy roots, and the results of this work should help guide the quality control of S. miltiorrhiza. In addition, the findings confirm that Mucor fragilis functions as an effective endophytic fungal elicitor with excellent application prospect for cultivation of medicinal plants.

Inducing red pigment and inhibiting citrinin production by adding lanthanum(III) ion in Monascus purpureus fermentation

Monascus pigments (MPs) are widely used natural colorants in Asian countries. The problems of low extracellular red pigment (ERP) and high citrinin remain to be solved in Monascus pigment production. The effect of lanthanum(III) ion (LaCl₃) on Monascus purpureus fermentation was investigated in this study. The yields of ERP and biomass respectively reached maxima of 124.10 U/mL and 33.10 g/L by adding 0.4 g/L La³⁺ on the second day in the total 8-day fermentation; simultaneously, citrinin was decreased by 59.93% and 38.14% in the extracellular and intracellular fractions, respectively. Reactive oxygen species (ROS) levels were obviously improved by La³⁺ treatment, while the activities of catalase (CAT) and superoxide dismutase (SOD) were increased compared with the control. The ratio of unsaturated/saturated fatty acids in mycelia was increased from 2.94 to 3.49, indicating that the permeability and fluidity of the cell membrane were enhanced under La³⁺ treatment. Gene expression analysis showed that the relative expression levels of Monascus pigment synthesis genes (pksPT, mppB, mppD, MpFasB2, and MpPKS5) were significantly upregulated by La³⁺ treatment, and in contrast, the relative expression levels of citrinin synthesis genes (ctnA, pksCT and mppC) were markedly downregulated. This work confirmed that LaCl₃ possesses the potential to induce red pigment biosynthesis and inhibit citrinin production in M. purpureus fermentation. KEY POINTS: • La³⁺ induced red pigment and inhibited citrinin production in Monascus fermentation. • La³⁺ regulated genes expression up for Monascus pigment and down for citrinin. • La³⁺ increased the UFAs in cell membrane to enhance the permeability and fluidity.

A living plant cell-based biosensor for real-time monitoring invisible damage of plant cells under heavy metal stress

Heavy metals inevitably cause invisible or visible damage to plants, leading to significant economic losses. Therefore, it is necessary to develop a method for timely monitoring the damage of plants under the stress of heavy metals. Here, vitronectin-like proteins (VN) on the surface of plant cells is as an important biomarker for monitoring damage of plants under the stress of heavy metals. A living plant cell-based biosensor is constructed to monitor invisible damage of plant cells induced by cadmium [Cd(II)] or lead [Pb(II)]. To fabricate this sensor, l-cysteine was first modified on the glassy carbon electrode followed by the modification of anti-IgG-Au antibody. Then, the living plant cells, incubated with the anti-VN, were modified onto the electrode. The sensor worked by determining the change in electrochemical impedance. Cd(II) and Pb(II) was detected in the linear dynamic range of 45-210 and 120-360 μmol·L^-1, respectively. And the detection limit of Cd(II) and Pb(II) of this biosensor was 18.5 nmol·L^-1 [with confidence interval (95%) 18.4-18.6 nmol·L^-1] and 25.6 nmol·L^-1 [with confidence interval (95%) 25.4-25.8 nmol·L^-1], respectively. In both Arabidopsis and soybean, when the content of VN increased by about 20 times under the stress of Cd(II) or Pb(II), which means when the electron-transfer resistance increased by 35%, chlorophyll content showed significant decrease about 17%. Therefore, by establishing a quantitative relationship among the content of biomarker, the electron-transfer resistance and chlorophyll content in plant cells, the invisible damage of plants under the stress of heavy metals was detected. These results can provide a reference method for early-onset warning systems for heavy metal pollution in the environment.

Structure of a polysaccharide from Trichoderma atroviride and its promotion on tanshinones production in Salvia miltiorrhiza hairy roots

This study evaluates the chemical structure of a heteropolysaccharide (PSF-W-1) from the endophytic fungus Trichoderma atroviride and its effects on the production of tanshinones in Salvia miltiorrhiza hairy roots. The total carbohydrate content of isolated PSF-W-1 was determined to be 97.72%. PSF-W-1 has a relative molecular weight of 36.13 kDa and contains mannose, glucose and galactose in molar ratios of 1.00:4.86:2.25. Through methylation analysis, IR and NMR, PSF-W-1 was determined to possess a backbone of →4)-β-D-Glcp-(1→6)-α-D-Galp-(1→4)-β-D-Manp-(1→6)-α-D-Galp-(1→ with two side chains β-D-Glcp-(1→4)-β-D-Glcp-(1→ attached to O3 of 1,6-α-D-Galp. Bioactivity tests suggested that PSF-W-1 was responsible for boosting the S. miltiorrhiza hairy root growth and the biosynthesis of dihydrotanshinone I, tanshinone I, tanshinone IIA and cryptotanshinone in hairy roots. According to this study, PSF-W-1 might be utilized as a potent stimulator of tanshinones synthesis.

A detection method in living plant cells for rapidly monitoring the response of plants to exogenous lanthanum

The pollution of rare earth elements (REEs) in ecosystem is becoming more and more serious, so it is urgent to establish methods for monitoring the pollution of REEs. Monitoring environmental pollution via the response of plants to pollutants has become the most stable and accurate method compared with traditional methods, but scientists still need to find the primary response of plants to pollutants to improve the sensitivity and speed of this method. Based on the facts that the initiation of endocytosis is the primary cellular response of the plant leaf cells to REEs and the detection of endocytosis is complex and expensive, we constructed a detection method in living plant cells for rapidly monitoring the response of plants to exogenous lanthanum [La(III), a representative of REEs] by designing a new immuno-electrochemical method for detecting the content change in extracellular vitronectin-like protein (VN) that are closely related to endocytosis. Results showed that when 30 μM La(III) initiated a small amount of endocytosis, the content of extracellular VN increased by 5.46 times, but the structure and function of plasma membrane were not interfered by La(III); when 80 μM La(III) strongly initiated a large amount of endocytosis, the content of extracellular VN increased by 119 times, meanwhile, the structure and function of plasma membrane were damaged. In summary, the detection method can reflect the response of plants to La(III) via detecting the content change in extracellular VN, which provides an effective and convenient way to monitor the response of plants to exogenous REEs.

Diverse responses of tanshinone biosynthesis to biotic and abiotic elicitors in hairy root cultures of Salvia miltiorrhiza and Salvia castanea Diels f. tomentosa

Salvia miltiorrhiza (S. miltiorrhiza) and Salvia castanea Diels f. tomentosa (S. castanea) are both used for treatment of cardiovascular diseases. They have the same bioactive compound tanshinones, but whose contents are hugely different. This study illustrated diverse responses of tanshinone biosynthesis to yeast extract (YE) and Ag⁺ in hairy roots of the two species. YE enhanced both the growth and tanshinone biosynthesis of two hairy roots, and contributed more to tanshinone accumulation in S. castanea than that in S. miltiorrhiza. Genes encoding 1-deoxy-d-xylulose 5-phosphate synthase (DXS2), geranylgeranyl diphosphatesynthase (GGPPS1), copalyl diphosphate synthase (CPS1), and two cytochromes P450 (CYP76AH1 and CYP76AH3) were also more responsive to YE in S. castanea than those in S. miltiorrhiza. Accumulations of dihydrotanshinone I and tanshinone I, and most biosynthetic genes in S. miltiorrhiza were more responsive to Ag⁺ than those in S. castanea. Accumulations of dihydrotanshinone I and cryptotanshinone were more responsive to YE, while tanshinone IIA accumulation was more responsive to Ag⁺ in S. miltiorrhiza. However, accumulations of other four tanshinones and related genes in S. castanea were more responsive to YE than Ag⁺. This study provides foundations for studying diverse specialized metabolism between the related species.

Phosphate starvation promoted the accumulation of phenolic acids by inducing the key enzyme genes in Salvia miltiorrhiza hairy roots

Phosphate starvation increased the production of phenolic acids by inducing the key enzyme genes in a positive feedback pathway in Saliva miltiorrhiza hairy roots. SPX may be involved in this process. Salvia miltiorrhiza is a wildly popular traditional Chinese medicine used for the treatment of coronary heart diseases and inflammation. Phosphate is an essential plant macronutrient that is often deficient, thereby limiting crop yield. In this study, we investigated the effects of phosphate concentration on the biomass and accumulation of phenolic acid in S. miltiorrhiza. Results show that 0.124 mM phosphate was favorable for plant growth. Moreover, 0.0124 mM phosphate was beneficial for the accumulation of phenolic acids, wherein the contents of danshensu, caffeic acid, rosmarinic acid, and salvianolic acid B were, respectively, 2.33-, 1.02-, 1.68-, and 2.17-fold higher than that of the control. By contrast, 12.4 mM phosphate inhibited the accumulation of phenolic acids. The key enzyme genes in the phenolic acid biosynthesis pathway were investigated to elucidate the mechanism of phosphate starvation-induced increase of phenolic acids. The results suggest that phosphate starvation induced the gene expression from the downstream pathway to the upstream pathway, i.e., a feedback phenomenon. In addition, phosphate starvation response gene SPX (SYG1, Pho81, and XPR1) was promoted by phosphate deficiency (0.0124 mM). We inferred that SPX responded to phosphate starvation, which then affected the expression of later responsive key enzyme genes in phenolic acid biosynthesis, resulting in the accumulation of phenolic acids. Our findings provide a resource-saving and environmental protection strategy to increase the yield of active substance in herbal preparations. The relationship between SPX and key enzyme genes and the role they play in phenolic acid biosynthesis during phosphate deficiency need further studies.