Solasodine accumulation in regenerated plants of Solanum torvum Sw

Acúmulo de solasodina em plantas micropropagadas de Solanum torvum Sw

Solasodine accumulation in regenerated plants of Solanum torvum Sw

Acúmulo de solasodina em plantas micropropagadas de Solanum torvum Sw

Moreira, C.B^I; Lima, S.S^I; Esquibel, M.A^I; Sato, A^I,II,*

^ILaboratório de Fisiologia Vegetal, Programa de Pós-Graduação em Biotecnologia Vegetal, Instituto de Biofísica Carlos Chagas Filho, Centro de Ciências da Saúde, Universidade Federal do Rio de Janeiro, CEP: 21941-590, Rio de Janeiro-Brasil

^IILaboratório de Cultura de Tecidos Vegetais, Departamento de Botânica, Escola de Ciências Biológicas, Universidade Federal do Rio de Janeiro, CEP: 22290-240, Rio de Janeiro-Brasil

ABSTRACT

A nodal segment culture was developed in order to assess Solanum torvum Sw. regeneration and solasodine levels. The influence of auxins (indoleacetic acid, 1-Naphthaleneacetic acid) and benzyl adenine on S. torvum growth in micropropagation was investigated. A nodal segment culture was initiated with seeds germinated in MS basal medium added of GA₃ and grown in different concentrations of IAA, IAA + BAP and NAA + BAP. Sixty-day-old plants from the in vitro culture were collected, frozen and lyophilized; then, the methyl orange method was used to quantify solasodine for the spectrophotometric assay. The best results regarding plant regeneration and solasodine accumulation were obtained by using the MS basal medium without addition of plant growth regulators; however, there was great production of calluses presenting friable bases. Based on these results, cell cultures can be initiated from such calluses with application of other auxins and cytokinins to enhance solasodine production, besides different elicitors, light intensities and sucrose concentrations.

Key words: Solanaceae, "Jurubeba", auxin, cytokinin, steroidal alkaloid

RESUMO

A regeneração de Solanum torvum e a avaliação do conteúdo de solasodina foram os objetivos de cultura de segmentos nodais. A influência de auxinas (ácido 3-indolacético, ácido naftalenoacético) e de 6-benzilaminopurina no crescimento de S. torvum na micropropagação foi investigado. Cultura de segmentos nodais foi iniciada por sementes germinadas em meio básico MS acrescido de GA₃ e cultivadas em diferentes concentrações de AIA, AIA + BAP e ANA + BAP. Plantas da cultura in vitro com 60 dias foram coletadas, congeladas e liofilizadas e o método de alaranjado de metila foi utilizado para quantificação de solasodina para o ensaio espectrofotométrico. Os melhores resultados para regeneração vegetal e acúmulo de solasodina foram alcançados no meio MS sem adição de reguladores de crescimento havendo, porém grande produção de calos de base friáveis. Esses resultados mostram que a partir desses calos, cultura de células pode ser iniciada com aplicação de outras auxinas e citocininas para o aumento da produção de solasodina além de diferentes eliciadores, intensidades luminosas e concentrações de sacarose.

Palavras-chave: Solanaceae, jurubeba, auxina, citocinina, alcalóide esteroidal

INTRODUCTION

Alkaloids are a class of nitrogen compounds structurally diverse, found in all plant groups, occurring most of them in angiosperms (Henriques et al., 2002; Hughes & Shanks, 2002). Solanaceae family presents several alkaloid groups and many plants accumulate steroidal alkaloids based on a C₂₇ cholestane skeleton, an important source of raw material to partial synthesis of steroidal hormones (Vieira & Carvalho, 1993; Esteves-Souza et al., 2002). The steroidal alkaloid solasodine has been reported to be accumulated in relatively high concentrations in a number of Solanum species. It can be converted to starter compound 16-dehydropregnenolone and has been used for the semi-synthetic production of pharmaceutical and contraceptive steroids in many parts of the world. In spite of the steroidal saponin diosgenin is the most important steroid from raw material (Figure 1), the high demand of this compound and problem with the supply of it have led researchers to look for alternative compounds (Galanes et al., 1984; Eltayeb et al., 1997).

The production of alkaloids in plant tissue culture by some solanaceous species have been presented in many reports as shown in Table 1 (Yamada & Hashimoto, 1982; Conner, 1987; Savary & Dougall, 1990; El-Ashaal et al., 1999; Khanam et al., 2000; Khanam et al., 2001; Okršlar et al., 2002; Kang et al., 2004; Jacob & Malpathak, 2005a; Jacob & Malpathak, 2005b; Bhat et al., 2008).

Solanum species which are found solasodine are easy to be cultivated because their high occurrence as herbs and ruderal shrubs, many times harmful in plant breeding (Vieira, 1998). Solanum torvum Sw. (Solanaceae), a medicinal plant known in Brazil as Jurubeba is indicated as sedative, diuretic and digestive (Mahmood et al., 1983; Corrêa, 1984; Ajaiyeoba, 1999; Chah et al., 2000). It is also considered a weed because its rapid spread in disturbed lands (Francis, 2007) but very common ingredient in Thai cuisine (Arthan et al., 2002).

The aim of this work was to study the in vitro development and solasodine production of the S. torvum plants from nodal segments culture.

MATERIAL AND METHOD

Fruits of S. torvum were collected in the Valonguinho campus of the Fluminense Federal University, Niterói, Rio de Janeiro and were identified by Drª Lúcia D'Ávila F. de Carvalho of Rio de Janeiro Botanical Garden Research Institute. A voucher specimen of this plant material is deposited in the Herbarium (RB 377.641) at Rio de Janeiro Botanical Garden Research Institute.

For the establishment of the tissue culture, seeds were surface sterilized twice with commercial liquid detergent for 15 minutes each time. In sterile chamber, they were washed with 70% (v/v) alcohol and then with 20% (v/v) commercial hypoclorite (2% active chlorine). Seeds were rinsed with sterile distilled water between steps. Seeds were germinated on Murashige and Skoog (MS) basal medium (Murashige & Skoog, 1962) added to 2.0 mg L^-1 gibberellic acid (GA₃).

Nodal segments were grown in sterile flasks with MS basal medium hormone free and added with 0.2 mg L^-1 indole acetic acid (IAA), 0.2 mg L^-1 IAA + 0.7 mg L^-1 benzyl adenine (BA), 0.2 mg L^-1 IAA + 1.6 mg L^-1 BA, 0.2 mg L^-1 naphthalene acetic acid (NAA) + 0.7 mg L^-1 BA at 28ºC ± 2ºC with 16 hours photoperiod and light intensity of 23 µmoles m^-2 s^-1. The development and elongation of new shoots and roots formation were verified after 60 days of culture.

The methyl orange method was used for solasodine quantification (Vieira, 1998). Each sample was divided in three aliquots and it was analyzed by spectrophotometric assay. Harvested plants from in vitro culture with 60 days old were frozen and lyophilized. The dried plants (3 g) were extracted in commercial ethanol-glacial acetic acid system (95:5), in reflux, for two hours. Afterwards, the extract was evaporated to dryness and reconstituted with 50 mL glacial acetic acid 10% (v/v) and boiled for thirty minutes. Then the extract was chilled, it was separated by filtration with paper filter. The material was warmed up about 70ºC and basified with NH₄OH to pH 9-10. The extract was frozen for twenty-four hours and then centrifuged for thirty minutes to 3500 rpm.

The waste obtained was dissolved in warm methanol and then added chloridric acid for 5 hours of reflux. Afterwards, the extract was evaporated to dryness and solubilised with methanol-glacial acetic acid (95:5) until 100 mL. From the methanol-glacial acetic acid solution 1 mL was solubilised with distilled water in a volumetric balloon (50 mL). From the aqueous solution 2 mL was passed to a volumetric balloon and added 5 mL of buffer solution of phosphates (pH 5.0) and 1 mL of methylorange solution 0.05%. The mixture was extracted with 25 mL of chloroform (5 X 5 mL) and to the chloroformic solution was added 2 mL of ethanol-sulphuric acid solution (98:2). The absorbance was read in 520 nm. The values found were transformed in percentage of solasodine/dry weight for the equation of the calibration curve obtained. The calibration curve was obtained according to Vieira (1998) utilizing external standard of solasodine.

In all of the experiments the layout was totally randomized. For growth regulators, tests were done in triplicate, n = 40 each time. Data was analyzed by variance test (ANOVA) and mean data were compared by Tukey test (significance of 5%). Rooting percentage was analyzed by difference of percentage test (p₁ and p₂), significance of 5%.

RESULT AND DISCUSSION

After 60 days of culture, plants grown in MS showed the best results for bud neoformation, shoot elongation and rooting. In this study, growth regulators supplementation reduced the height; bud neoformation number and rooting in regard to MS control (Table 2).

The formation of white to white-brown basal calli was observed on nodal segments under effect of growth regulators tested and concomitantly reduction of shoots production and elongation.

The induction of small organogenic callus in leaf explants of Duboisia myoporoides (Solanaceae) grown in MS medium added with 1 µM IAA and 10 µM BA was reported after four weeks of culture (Khanam et al., 2000). In the present work, S. torvum nodal segments showed the formation of basal calli but there was no organogenesis. Hypocotyl explants of S. torvum under effect of NAA (0.1-1.0 mg L^-1) and BA (0.2-2.0 mg L^-1) on MS medium had developed shoots and organogenic calli (Jaiswal & Narayan, 1985). On leaf explants of Solanum nigrum and S. nigrum var. judaicum, calli were formed in NAA (0.5-4.0 mg L^-1) with BA (0.5 mg L^-1) on MS medium. In this case, the combination of 0.5 mg L^-1 for both regulators resulted on the highest index of regeneration (El-Ashaal et al., 1999). From these studies it can be concluded that the combination of NAA + BA was very efficient to induction of indirect organogenesis, although in S. torvum nodal segments, the formation of basal calli were observed only without organogenesis.

Nodal segments of S. torvum presented roots in over 98% of the explants in MS medium added to 0.2 mg L^-1 IAA and when it was added 1.6 mg L^-1 BA to the medium, rooting rate have dropped. In MS medium added to NAA and BA concentrations nodal segments produced over 90% of plants rooted in 60 days of culture.

The production of solasodine by in vitro culture was affected to a significant extent by plant growth regulators added to medium culture. Plants grown in MS media produced more solasodine than those grown in MS with auxins and cytokinin added (Table 2).

Auxins have been shown to inhibit alkaloid biosynthesis and accumulation. In Catharanthus roseus cell cultures, auxins exerted a dramatic reduction on alkaloid terpenoid precursors availability (Gantet et al., 1997). Auxins have also been shown to down-regulate gene expression in alkaloid biosynthesis. In C. roseus cell cultures the sss gene (for strictosidine synthase) and tdc gene (for tryptophan decarboxylase) was rapidly down regulated by auxin (Pasquali et al., 1992). However, it was showed that NAA applications did not affect leaf camptothecin concentration (Li & Liu, 2003).

Cytokinins have also been shown to be involved in plant secondary metabolism. For example, cytokinins stimulate alkaloid biosynthesis in cell lines of C. roseus and Fagara zanthoxyloides (Decendit et al., 1992; Coillerot et al., 1996; Carpin et al., 1997). On the other hand, it was reported that BA applications do not improve total leaf camptothecin (Li & Liu, 2003).

Regenerated plants that had been developed high basal calli, presented lower elongation consequently less photosensitizing tissues. In S. laciniatum this fact alters solasodine biosynthesis on leaves since the synthesis is dependent or promoted in active chloroplast (Conner, 1987). It was also observed on green root culture of Datura stramonium the increment of alkaloid production and subsequent decrease of the production when this culture was transferred to dark conditions (Flores et al., 1993). This type of culture might be the key for high production of the solasodine since this compound was firstly detected and this accumulation occurs on green parts of the plants, e.g. leaves and immature fruits (Kittipongpatana et al., 1998).

It was reported a great production of glycoalkaloids (solasonine, solamargine and solanine) on leaf culture of Solanum nigrum and Solanum nigrum var. judaicum on MS + 0.5 mg L^-1 NAA + 0.5 mg L^-1 BA (El-Ashaal et al., 1999). The results of this work are controversy since lower solasodine accumulation on regenerated plants were obtained when cultivated on the same combination of plant growth regulators.

The evaluation of solasodine content on in vitro plants of S. torvum showed that on MS medium with no plant growth regulators, the content was 13.4 mg solasodine g^-1 DW (1.34%) as higher as the most competitive species that produced on leaves, from field plants, from 1.6 to 3.8% (Vieira & Carvalho, 1993).

It was mentioned that a number of factors might influence the in vitro accumulation of solasodine on S. aviculare as basic medium of culture, sucrose concentration, type and concentration of plant growth regulators and the combinations of overall factors (Kittipongpatana et al., 1998). Also, the salinity stress in S. nigrum offers possibility of enhanced production of solasodine, using NaCl as an efficient and economical elicitor source (Bhat et al., 2008).

From the biotechnological point of view, S. torvum is a species that must be investigated in future work since the in vitro production of solasodine have been a desired target and it has been potential alternative to diosgenin for commercial steroid drug synthesis (Galanes et al., 1984). Also the price of diosgenin increased dramatically in the 90's, therefore the search for suitable alternative remains a viable area of research. The success in obtaining a method for high production of solasodine, might very well be one of the solutions for this problem in the future.

It was investigated the relation between growth and solasodine production manipulating the components in MS and Gamborg's B5 media in hairy root cultures of Solanum khasianum (Jacob & Malpathak, 2005a). Thus it was concluded that optimization of appropriate root line with a high growth rate and secondary metabolism shall help in a scale up of solasodine production in suitable bioreactors. Meanwhile, in hairy roots culture of S. khasianum, the presence of shoots as an alternate sink for the steroidal alkaloid extended the exponential growth phase of the culture and it can be used to achieve optimum hairy root culture performance for increased solasodine production and low permeabilization into the medium (Jacob & Malpathak, 2005b)

In vitro plants of Solanum torvum showed the capacity to produce alkaloids. MS basal medium was the best culture conditions for solasodine accumulation (1.34% DW). IAA (0.2 mg L^-1) and BA (0.7 and 1.6 mg L^-1) and also NAA (0.2 mg L^-1) and BA (0.7 mg L^-1) applications in growth media decreased the bud neoformation/explant, shoot elongation and rooting percentage in nodal segment culture and also inhibited the solasodine accumulation in regenerated plants, however growth regulators combinations induced high production of friable basal calli. These results show that, for further studies, in vitro cell culture can be initiated with others auxin and cytokinin for enhancing in vitro production of solasodine besides different elicitors, light intensities and sucrose concentrations.

ACKNOWLEDGEMENT

The authors thank Drª Lúcia D'Ávila F. de Carvalho from Rio de Janeiro Botanical Garden Research Institute by taxonomic identification. We are very grateful to Drª Rita de Cássia Almeida Lafetá for providing purified solasodine.

Recebido para publicação em 12/12/2008

Aceito para publicação em 29/10/2009

• AJAIYEOBA, E.O. Comparative phytochemical and antimicrobial studies of Solanum macrocarpum and S. torvum leaves. Fitoterapia, v.70, p.184-6, 1999.
• ARTHAN, D. et al. Antiviral isoflavonoid sulfate and steroidal glycosides from the fruits of Solanum torvum Phytochemistry, v.59, p.459-63, 2002.
• BHAT, M.A. et al. Salinity stress enhances production of solasodine in Solanum nigrum L. Chemical and Pharmaceutical Bulletin, v.56, p.17-21, 2008.
• CARPIN, S. et al. The relationship between the accumulation of a 28 kD polypeptide and that of indole alkaloids in Catharanthus roseus cell suspension cultures. Journal of Plant Physiology, v.150, p.452-7, 1997.
• CHAH, K.F.; MUKO, K.N.; OBOEGBULEM, S.I. Antimicrobial activity of methanolic extract of Solanum torvum fruit. Fitoterapia, v.71, p.187-9, 2000.
• COILLLEROT, E. et al. Furoquinoline alkaloid accumulation in Fagara zanthoxyloides cell cultures is highly dependent on the presence of exogenous benzylaminopurine. Plant Growth Regulation, v.19, p.203-6, 1996.
• CONNER, A.J. Differential solasodine accumulation in photoautotrophic and heterotrophic tissue cultures of Solanum laciniatum Phytochemistry, v.26, p.2749-50, 1987.
• CORRÊA, M.P. Dicionário das plantas úteis do Brasil e das exóticas cultivadas 3.ed. Rio de Janeiro: Ministério da Agricultura/IBDF, 1984. 533p.
• DECENDIT, A. et al. Cytokinin-enhanced accumulation of indole alkaloids in Catharanthus roseus cell cultures: the factors affecting the cytokinin response. Plant Cell Reports, v.11, p.400-3, 1992.
• EL-ASHAAL, H.A. et al. Alkaloid production from regenerated Solanum parts. Fitoterapia, v.70, p. 407-11, 1999.
• ELTAYEB, E.A.; AL-ANSARI, A.S.; RODDICK, J.G. Changes in the steroidal alkaloid solasodine during development of Solanum nigrum and Solanum incanum Phytochemistry, v.46, p.489-94, 1997.
• ESTEVES-SOUZA, A. et al. Cytotoxic activities against Ehrlich carcinoma and human K562 leukaemia of alkaloids and flavonoid from two Solanum species. Journal of the Brazilian Chemical Society, v.13, p.838-42, 2002.
• FLORES, H.E. et al. Green roots: photosynthesis and photoautotrophy in an underground plant organ. Plant Physiology, v.101, p.363-71, 1993.
• FRANCIS, J.K. Solanum torvum Sw. (Solanaceae): turkey berry Disponível em: <http://www.fs.fed.us/global/iitf/pdf/shrubs/Solanum%20torvum.pdf>. Acesso em: 22 abr. 2007.
• GALANES, I.T.; WEBB, D.T.; ROSARIO, O. Steroid production by callus and cell suspension cultures of Solanum aviculare. Journal of Natural Products, v.47, p.373-6, 1984.
• GAMBORG, O.L.; MILLER, R.A.; OJIMA, K. Nutrient requirements of suspension cultures of soybean root cells. Experimental Cell Research, v.50, p.151-8, 1968.
• GANTET, P. et al. Inhibition of alkaloid accumulation by 2,4 D in Catharanthus roseus cell suspension is overcome by methyl jasmonate. Acta Botanica Gallica, v.122, p.783-6, 1997.
• HENRIQUES, A.T.; KERBER, V.A.; MORENO, P.R.H. Alcalóides: generalidades e aspectos básicos. In: SIMÕES, C.M.O. et al. (Ed.). Farmacognosia: da planta ao medicamento. Porto Alegre/Florianópolis: UFRGS/UFSC, 2002. p.651-6.
• HUGHES, E.H.; SHANKS, J.V. Metabolic engineering of plants for alkaloid production. Metabolic Engineering, v.4, p.41-8, 2002.
• JACOB, A.; MALPATHAK, N. Manipulation of MS and B5 components for enhancement of growth and solasodine production in hairy root cultures of Solanum khasianum Clarke. Plant Cell, Tissue and Organ Culture, v.80, p.247-57, 2005a.
• JACOB, A.; MALPATHAK, N. Plantlet regeneration enhances solasodine productivity in hairy root culture of Solanum khasianum Clarke. In Vitro Cellular and Developmental Biology - Plant, v.41, p.291-5, 2005b.
• JAISWAL, V.S.; NARAYAN, P. Plantlet regeneration from hypocotyl callus of Solanum torvum Swartz. Journal of Plant Physiology, v.119, p.381-3, 1985.
• KANG, Y.M. et al. Rapid in vitro adventitious shoot propagation of Scopolia parviflora through rhizome cultures for enhanced production of tropane alkaloids. Plant Cell Reports, v.23, p.128-33, 2004.
• KHANAM, N. et al. Organogenesis, differentiation and histolocalization of alkaloids in cultured tissues and organs of Duboisia myoporoides R. Br. Annals of Botany, v.86, p.745-52, 2000.
• KHANAM, N. et al. Tropane alkaloid production by shoot culture of Duboisia myoporoides R. Br. Phytochemistry, v.56, p.59-65, 2001.
• KITTIPONGPATANA, N.; HOCK, R.S.; PORTER, J.R. Production of solasodine by hairy root, callus, and cell suspension cultures of Solanum aviculare Forst. Plant Cell, Tissue and Organ Culture, v.52, p.133-43, 1998.
• LI, Z.; LIU, Z. Effects of benzyladenine and naphthalene acetic acid on growth and camptothecin accumulation in Camptotheca acuminata seedlings. Plant Growth Regulation, v.22, p.205-16, 2003.
• LINSMAIER, E.M.; SKOOG, F. Organic growth factor requirements of tobacco tissue culture. Physiologia Plantarum, v.18, p.100-27, 1965.
• MAHMOOD, U.; SHUKLA, N.; THAKUR, R.S. Non-alkaloidal constituents from Solanum torvum leaves. Phytochemistry, v.22, p.164-9, 1983.
• MURASHIGE, T.; SKOOG, F. A revised medium for rapid growth and bioassays with tobacco tissue cultures. Physiologia Plantarum, v.15, p.473-97, 1962.
• OKRLAR, V. et al. Micropropagation and hairy root culture of Solanum laciniatum Ait. In vitro cellular and developmental biology. Plant, v.38, p.352-7, 2002.
• PASQUALI, G. et al. Coordinated regulation of two indole alkaloid biosynthetic genes from Catharanthus roseus by auxin and elicitors. Plant Molecular Biology, v.18, p.1121-31, 1992.
• SAVARY, B.J.; DOUGALL, D.K. Scopolamine radioimmunoassay for tissue cultures of Datura Phytochemistry, v.29, p.1567-9, 1990.
• VIEIRA, R.F. Alcalóides esteroidais do gênero Solanum: avaliação quantitativa do teor de solasodina em frutos verdes de Solanum mauritianum Scop. In: MING, L.C. et al. (Ed.). Plantas Medicinais, aromáticas e condimentares: avanços na pesquisa agronômica. Botucatu: Unesp, 1998. p.169-91.
• VIEIRA, R.F.; CARVALHO, L.D.F. Espécies medicinais do gênero Solanum produtoras de alcalóides esteroidais. Revista Brasileira de Farmácia, v.74, p.97-111, 1993.
• YAMADA, Y.; HASHIMOTO, T. Production of tropane alkaloids in cultured cells of Hyoscyamus niger Plant Cell Reports, v.1, p.101-3, 1982.

Publication Dates

• Publication in this collection
  11 Nov 2010
• Date of issue
  Mar 2010

History

• Received
  12 Dec 2008
• Accepted
  29 Oct 2009