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Medicinal and Aromatic Plants I pp 136–156Cite as

Immobilization of Higher Plant Cells

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Part of the book series: Biotechnology in Agriculture and Forestry ((AGRICULTURE,volume 4))

Abstract

The initial interest in the immobilization of cultured plant cells was stimulated by the potential advantages of immobilized systems over free cell systems for the production of metabolites (Brodelius et al. 1979). It has since been demonstrated that cell immobilization has certain additional advantageous physiological effects. However, despite the resultant increase in the use of immobilized systems for the study of a variety of phenomena, attention still remains centred upon their use for the production of phytochemicals, as reflected by the balance of the contents of this chapter. It is, perhaps, something of a paradox that the great interest expressed in this subject, as exemplified by the number of recent reviews, has not been accompanied by a parallel increase in the number of research papers. Nevertheless, we believe that plant cell immobilization will become one of the important techniques used by plant biotechnologists to achieve a range of economically viable, commercial processes using plant cell cultures. The ability to immobilize plant cells has been demonstrated for a large number of higher plant cells and protoplasts (Table 1) using a variety of polymeric matrices. In our searches of the literature we have found no reference to the failure to immobilize cultured cells of any species tested. In this chapter is presented a review of the rationale and techniques used for the immobilization of plant cells, emphasizing the advantages and limitations of the published methods and the extent of their application.

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References

  • Adams TL, Townsend JA (1983) A new procedure for increasing efficiency of protoplast plating and clone selection. Plant Cell Rep 2:165–168.

    Article  CAS  Google Scholar 

  • Alfermann AW, Schuler I, Reinhard E (1980) Biotransformation of cardiac glycosides by immobilized cells of Digitalis lanata. Planta Medica 40:218–223.

    Article  CAS  Google Scholar 

  • Alfermann AW, Bergmann W, Figur C, Helmbold U, Schwantag D, Schuler I, Reinhard E (1983) Biotransformation of β-methyldigitoxin to β-methyldigoxin by cell cultures of Digitalis lanata. In: Mantell SH, Smith H (eds) Plant biotechnology. Univ Press, Cambridge, pp 67–74.

    Google Scholar 

  • Archambault J, Volesky B, Kurz WGW (1986) Surface immobilization of plant cells. In: Somers DA, Gengenbach BG, Biesboer DD, Hacket WP, Green CE (eds) Proc VIth Int Congr Plant tissue and cell culture, vol 1. IAPTC, Minneapolis, p 451.

    Google Scholar 

  • Ayabe S, Iida K, Furuya T (1986) Induction of stress metabolites in immobilized Glycyrrhiza echinata cultured cells. Plant Cell Rep 5:186–189.

    Article  CAS  Google Scholar 

  • Beiderbeck R (1982) Two-phase culture — a method for the isolation of lipophilic substances from plant suspension cultures. Z Pflanzenphysiol 108:27–30.

    CAS  Google Scholar 

  • Berlin J (1985) The use of immobilized plant cells — an evaluation. IAPTC Newslett 46:8–14.

    Google Scholar 

  • Berlin J, Witte L, Schubert W, Wray V (1984) Determination and quantification of monoterpenoids secreted into the medium of cell cultures of Thuja occidentalis. Phytochemistry 23:1277–1279.

    Article  CAS  Google Scholar 

  • Bohm H (1978) Regulation of alkaloid production in plant cell cultures. In: Thorpe TA (ed) Frontiers of plant tissue culture 1978. Univ Press, Calgary, pp 201–211.

    Google Scholar 

  • Bornmann CH, Zachrisson A (1982) Immobilization of protoplasts by anchoring to microcarriers. Plant Cell Rep 1:151–153.

    Article  Google Scholar 

  • Brodelius P (1983) Production of biochemicals with immobilized plant cells. Ann NY Acad Sci 413:383–393.

    Article  CAS  Google Scholar 

  • Brodelius P (1985a) Immobilized plant cells. In: Laskin AI (ed) Enzymes and immobilized cells in biotechnology. Benjamin, Cummings, CA, pp 109–148.

    Google Scholar 

  • Brodelius P (1985b) Immobilized plant cells: preparation and biosynthetic capacity. In: Woodward J (ed) Immobilized cells and enzymes, a practical approach. IRL, Washington DC, pp 127–145.

    Google Scholar 

  • Brodelius P, Mosbach K (1982) Immobilized plant cells. Adv Appl Microbiol 28:1–26.

    Article  PubMed  CAS  Google Scholar 

  • Brodelius P, Nilsson K (1980) Entrapment of plant cells in different matrices. FEBS Lett 122:312–316.

    Article  CAS  Google Scholar 

  • Brodelius P, Nilsson K (1983) Permeabilization of immobilized plant cells, resulting in release of intracellulary stored products with preserved cell viability. Eur J Appl Microbiol Biotechnol 17:275–280.

    Article  CAS  Google Scholar 

  • Brodelius P, Deus B, Mosbach K, Zenk MH (1979) Immobilized plant cells for the production and transformation of natural products. FEBS Lett 103:93–97.

    Article  PubMed  CAS  Google Scholar 

  • Butcher DN, Connolly JD (1971) An investigation of factors which influence the production of abnormal terpenoids by callus cultures of Andrographis paniculata. J exp Bot 22:314–322.

    Article  CAS  Google Scholar 

  • Curtin ME (1983) Harvesting profitable products from plant tissue culture. Bio/Technology 1:649–657.

    Article  Google Scholar 

  • Dainty AL, Goulding KH, Robinson PK, Simpkins I, Trevan MD (1985) Effect of immobilization on plant cell physiology — real or imaginary? Trends Biotechnol 3:59–60.

    Article  Google Scholar 

  • Deus-Neumann B, Zenk MH (1984a) Instability of indole alkaloid production in Catharanthus roseus cell suspension cultures. Planta Medica 50:427–431.

    Article  PubMed  CAS  Google Scholar 

  • Deus-Neumann B, Zenk MH (1984b) A highly selective alkaloid uptake system in vacuoles of higher plants. Planta 162:250–260.

    Article  CAS  Google Scholar 

  • Deus-Neumann B, Zenk MH (1986) Accumulation of alkaloids in plant vacuoles does not involve an ion-trap mechanism. Planta 167:44–53.

    Article  CAS  Google Scholar 

  • Felix HR, Brodelius P, Mosbach K (1981) Enzyme activities of the primary and secondary metabolism of simultaneously permeabilized and immobilized cells. Analyt Biochem 116:462–470.

    Article  PubMed  CAS  Google Scholar 

  • Fowler MW (1983) Commercial applications and economic aspects of mass plant cell culture. In: Mantell SH, Smith H (eds) Plant biotechnology. Univ Press, Cambridge, pp 3–38.

    Google Scholar 

  • Fowler MW (1986) Process strategies for plant cell cultures. Trends Biotechnol 4:214–218.

    Article  Google Scholar 

  • Fuller KW, Bartlett DJ (1985) The chemosynthetic potential of plants and its realisation by immobilized systems. Annu Proc Phytochem Soc Eur 26:229–247.

    Google Scholar 

  • Furuya T, Yoshikawa T, Taira M (1984) Biotransformation of codeinone to codeine by immobilized cells of Papaver somniferum. Phytochemistry 23:999–1002.

    Article  CAS  Google Scholar 

  • Galun E, Aviv D, Dantes A, Freeman A (1983) Biotransformation by plant cells immobilized in cross-linked polyacrylamide-hydrazine. Planta Med 49:9–13.

    Article  PubMed  CAS  Google Scholar 

  • Galun E, Aviv D, Dantes A, Freeman A (1985) Biotransformation by division-arrested and immobilized plant cells: Bioconversion of monoterpenes by Gamma-irradiated, suspended and entrapped cells of Mentha and Nicotiana. Planta Med 51:511–514.

    Article  PubMed  CAS  Google Scholar 

  • Goldstein WE (1983) Large-scale processing of plant cell cultures, Ann NY Acad Sci 413:394–408.

    Article  Google Scholar 

  • Hahlbrock K, Grisebach H (1979) Enzymic controls in the biosynthesis of lignins and flavenoids. Ann Rev Plant Physiol 30:105–130.

    Article  CAS  Google Scholar 

  • Haldimann D, Brodelius P (1986) Changes of methylxanthin-pattern in high alkaloid producing immobilized cells of Coffea arabica. In: Somers DA, Gengenbach BG, Biesboer DD, Hackett WP, Green CE (eds) Proc VIth Int Congr Plant tissue and cell culture, vol 1. IAPTC, Minneapolis, p 349.

    Google Scholar 

  • Hall RD, Yeoman MM (1986a) Temporal and spatial heterogeneity in the accumulation of antho-cyanins in cell cultures of Catharanthus roseus. J exp Bot 37:48–60.

    Article  CAS  Google Scholar 

  • Hall RD, Yeoman MM (1986b) Factors determining anthocyanin yield in cell cultures of Catharanthus roseus. New Phytol 103:33–43.

    Article  CAS  Google Scholar 

  • Hall RD, Holden MA, Yeoman MM (1986a) Studies on the regulation of capsaicin biosynthesis in immobilized cell cultures and the developing fruit of the chilli pepper Capsicum frutescens. In: Morris P, Scragg AH, Stafford A, Fowler MW (eds) Secondary metabolism in plant cell cultures. Univ Press, Cambridge, pp 121–127.

    Google Scholar 

  • Hall RD, Holden MA, Yeoman MM (1986b) The accumulation of phenylpropanoid and capsaicinoid compounds in cell cultures and whole fruit of the chilli pepper C. frutescens. Plant Cell Tiss Org Cult 8:163–176.

    Article  Google Scholar 

  • Hamilton R, Pedersen H, Chin C-K (1984) Immobilized plant cells for the production of biochemicals. Biotechnol Bioeng Symp 14:383–396.

    CAS  Google Scholar 

  • Holden MA, Hall RD, Lindsey K, Yeoman MM (1987a) Capsaicin biosynthesis in cell cultures of Capsicum frutescens. In: Webb C, Mavituna F, Faria JJ (eds) Process possibilities for plant and animal cell cultures. Inst Chem Eng, pp 46-63.

    Google Scholar 

  • Holden MA, Hall RD, Yeoman MM (1987b) Incorporation of cell-wall-bound cinnamic acid derivatives into capsaicin in cultured cells of the chilli pepper Capsicum frutescens. In: Webb C, Mavituna F, Faria JJ (eds) Process possibilities for plant and animal cell cultures. Inst Chem Eng, pp 297-300.

    Google Scholar 

  • Jirku V, Macek T, Vanek T, Krumphanzl V, Kubanek V (1981) Continuous production of steroid glycoalkaloids by immobilized plant cells. Biotechnol Lett 3:447–450.

    Article  CAS  Google Scholar 

  • Jones A, Veliky A (1981) Effect of medium constituents on the viability of immobilized plant cells. Can J Bot 59:2095–2101.

    Article  CAS  Google Scholar 

  • Jose W, Pedersen H, Chin C-K (1983) Immobilization of plant cells in a hollow-fibre reactor. Ann NY Acad Sci 413:409–412.

    Article  Google Scholar 

  • Kilby NJ, Hunter CS (1986) Ultrasonic stimulation of betanin release from Beta vulgaris cells in vitro. In: Somers DA, Gengenbach BG, Biesboer DD, Hackett WP, Green CE (eds) Proc VIth Int Congr Plant tissue and cell culture, vol 1. IAPTC, Minneapolis, p 352.

    Google Scholar 

  • Kitto S, Janick J (1982) Polyox as an artificial seed coat for asexual embryos. Hort Sci 17:448.

    Google Scholar 

  • Knorr D, Teutonico RA (1986) Chitosan immobilization and permeabilization of Amaranthus tricolor. J Agric Food Chem 34:96–97.

    Article  CAS  Google Scholar 

  • Knorr D, Miazga SM, Teutonico RA (1985) Immobilization and permeabilization of cultured plant cells. Food Technol 39:135–142.

    Google Scholar 

  • Kurz WGW, Constabel F (1979) Plant cell cultures, a potential source of pharmaceuticals. Adv Appl Microbiol 25:209–240.

    Article  PubMed  CAS  Google Scholar 

  • Lambe CA, Rosevear A (1983) Immobilized plant cells. Proc Biotech 83:565–576.

    Google Scholar 

  • Lindsey K (1985) Manipulation, by nutrient limitation, of the biosynthetic activity of immobilized cells of Capsicum frutescens Mill. cv. annuum. Planta 165:126–133.

    Article  CAS  Google Scholar 

  • Lindsey K (1986) Incorporation of [14C]phenylalanine and [14C]cinnamic acid into capsaicin in cultured cells of Capsicum frutescens. Phytochemistry 25:2793–2801.

    Article  CAS  Google Scholar 

  • Lindsey K, Yeoman MM (1983a) Novel experimental systems for studying the production of secondary metabolites by plant tissue cultures. In: Mantell SH, Smith H (eds) Plant biotechnology. Soc Exp Biol Seminar Ser 18:39–66 Univ Press, Cambridge.

    Google Scholar 

  • Lindsey K, Yeoman MM (1983b) The relationship between growth rate, differentiation and alkaloid accumulation in cell cultures. J exp Bot 34:1055–1065.

    Article  CAS  Google Scholar 

  • Lindsey K, Yeoman MM (1984a) The synthetic potential of immobilized cells of Capsicum frutescens. Planta 162:495–501.

    Article  CAS  Google Scholar 

  • Lindsey K, Yeoman MM (1984b) The viability and biosynthetic activity of cells of Capsicum frutescens immobilized in reticulate polyurethane. J exp Bot 35:1684–1696.

    Article  CAS  Google Scholar 

  • Lindsey K, Yeoman MM (1986) Immobilized plant cells. In: Yeoman MM (ed) Plant cell culture technology. Blackwell, Oxford, pp 228–270.

    Google Scholar 

  • Lindsey K, Yeoman MM, Black GM, Mavituna F (1983) A novel method for the immobilization and culture of plant cells. FEBS Lett 155:143–149.

    Article  CAS  Google Scholar 

  • Linsefors L, Brodelius P (1985) Immobilization of plant protoplasts: viability studies. Plant Cell Rep 4:23–27.

    Article  CAS  Google Scholar 

  • Lörz H, Larkin PJ, Thomson J, Scowcroft WR (1983) Improved protoplast culture and agarose media. Plant Cell Tiss Org Cult 2:217–226.

    Article  Google Scholar 

  • Luckner M (1980) Expression and control of secondary metabolism. In: Bell EA, Charlwood BV (eds) Encyclopedia of plant physiology, New Ser, vol 8. Springer, Berlin Heidelberg New York, pp 23–64.

    Google Scholar 

  • Majerus F, Pareilleux A (1986) Alkaloid accumulation in Ca-alginate entrapped cells of Catharanthus roseus: using a limiting growth medium. Plant Cell Rep 5:302–305.

    Article  CAS  Google Scholar 

  • Mantell SH, Smith H (1983) Cultural factors that influence secondary metabolite accumulation in plant cell and tissue cultures. In: Mantell SH, Smith H (eds) Plant biotechnology. Univ Press, Cambridge, pp 75–110.

    Google Scholar 

  • Mavituna F, Park JM, Williams PD, Wilkinson AK (1987) Characteristics of immobilized plant cell reactors. In: Webb C, Mavituna F, Faria JJ (eds) Process possibilities for plant and animal cell cultures. Inst Chem Eng (in press).

    Google Scholar 

  • Miyasaka H, Nasu M, Yamamoto T, Endo Y, Yoneda K (1986) Production of cryptotanshinone and ferruginol by immobilized cultured cells of Salvia miltiorrhiza. Phytochemistry 25:1621–1624.

    Article  CAS  Google Scholar 

  • Morris P, Smart NJ, Fowler MW (1983) A fluidised bed vessel for the culture of immobilized plant cells and its application for the continuous production of fine cell suspensions. Plant Cell Tiss Org Cult 2:207–216.

    Article  Google Scholar 

  • Nakagawa K, Konagai A, Fukui H, Tabata M (1984) Release and crystallization of berberine in the liquid medium of Thalictrum minus cell suspension cultures. Plant Cell Rep 3:254–257.

    Article  CAS  Google Scholar 

  • Nakajima H, Sonomoto K, Usui N, Sato F, Yamada Y, Tanaka A, Fukui S (1985) Entrapment of Lavandula vera cells and production of pigments by entrapped cells. J Biotechnol 2:107–117.

    Article  CAS  Google Scholar 

  • Parr AJ, Robins RJ, Rhodes MJC (1987) Release of secondary products by plant cell cultures. In: Webb C, Mavituna F, Faria JJ (eds) Process possibilities for plant and animal cell cultures. Inst Chem Eng (in press).

    Google Scholar 

  • Phillips R, Henshaw GG (1977) The regulation of synthesis of phenolics in stationary phase cell cultures of Acer pseudoplatanus L. J exp Bot 28:785–794.

    Article  CAS  Google Scholar 

  • Prenosil JE, Pedersen H (1983) Immobilized plant cell reactors. Enz Microb Technol 5:323–331.

    Article  CAS  Google Scholar 

  • Redenbaugh K, Paasch BD, Nichol JW, Kossler ME, Viss PR, Walker KA (1986) Somatic seeds: encapsulation of asexual plant embryos. Bio/Technology 4:797–801.

    Article  Google Scholar 

  • Rhodes MJC (1985) Immobilized plant cell cultures. Top Enz Ferment Biotechnol 10:51–87.

    CAS  Google Scholar 

  • Rhodes MJC, Kirsop BH (1982) Plant cell cultures as sources of valuable secondary products. Biologist 29:134–140.

    Google Scholar 

  • Rhodes MJC, Robins RJ, Turner RJ, Smith JI (1985) Mucilaginous film production by plant cells immobilized in a polyurethane or nylon matrix. Can J Bot 63:2357–2363.

    Article  Google Scholar 

  • Rosevear A, Lambe CA (1985) Immobilized plant cells. Adv Biochem Eng 31:37–58.

    CAS  Google Scholar 

  • Sahai O, Knuth M (1985) Commercializing plant tissue culture processes: economics, problems and prospects. Biotechnol Progr 1:1–9.

    Article  CAS  Google Scholar 

  • Sato F, Yamada Y (1984) High berberine-producing cultures of Coptis japonica cells. Phytochemistry 23:281–285.

    Article  CAS  Google Scholar 

  • Scheurich P, Schnabl H, Zimmermann U, Klein J (1980) Immobilization and mechanical support of individual protoplasts. Biochem Biophys Acta 598:645–651.

    Article  PubMed  CAS  Google Scholar 

  • Schnabl H, Youngman RJ (1985) Immobilization of plant cell protoplasts inhibits enzymic lipid peroxidase. Plant Sci 40:65–69.

    Article  CAS  Google Scholar 

  • Schnabl H, Scheurich P, Zimmermann U (1980) Mechanical stabilization of guard cell protoplasts of Vicia faba. Planta 149:280–282.

    Article  CAS  Google Scholar 

  • Schnabl H, Youngman RJ, Zimmermann U (1983a) Maintenance of plant cell membrane integrity and function by the immobilization of protoplasts in alginate matrices. Planta 158:392–397.

    Article  CAS  Google Scholar 

  • Schnabl H, Elbert C, Youngman RJ (1983b) Release of ethane from immobilized plant cell protoplasts in response to chemical treatment. Physiol Plant 59:46–49.

    Article  CAS  Google Scholar 

  • Schuler M (1981) Production of secondary metabolites from plant tissue culture — problems and prospects. Ann NY Acad Sci 369:65–79.

    Article  Google Scholar 

  • Schuler ML, Sahai OP, Hallsby GA (1983) Entrapped plant cell cultures. Ann N Y Acad Sci 413:373–412.

    Article  Google Scholar 

  • Shillito RD, Paszkowski J, Potrykus I (1983) Agarose plating and a bead-type culture technique enable and stimulate development of protoplast-derived colonies in a number of plant species. Plant Cell Rep 2:244–247.

    Article  CAS  Google Scholar 

  • Tanaka H, Hirao C, Semba H, Tozawa Y, Ohmomo S (1985) Release of intracellularly stored 5′-phosphodiesterase with preserved plant cell viability. Biotechnol Bioeng 27:890–892.

    Article  PubMed  CAS  Google Scholar 

  • Tramper J (1985) Immobilizing biocatalysts for use in synthesis. Trends Biotechnol 3:45–50.

    Article  CAS  Google Scholar 

  • Veliky IA, Jones A (1981) Bioconversion of gitoxigenin by immobilized plant cells in a column bioreactor. Biotechnol Lett 3:551–554.

    Article  CAS  Google Scholar 

  • Warren GS, Fallon R (1984) Reversible lectin-mediated immobilization of plant protoplasts on agarose beads. Planta 161:201–206.

    Article  CAS  Google Scholar 

  • Watts MJ, Collin HA (1985) Growth and nutrient uptake by immobilized tissue culture cells of celery (Apium graveolens). Plant Sci Lett 42:67–72.

    Article  CAS  Google Scholar 

  • Wichers HJ, Malingre TM, Huizing HJ (1983) The effect of some environmental factors on the production of L-DOPA by alginate-entrapped cells of Mucuna pruriens. Planta 158:482–486.

    Article  CAS  Google Scholar 

  • Yeoman MM (1987) Techniques, characteristics, properties and commercial potential of immobilized plant cells. In: Constabel F, Vasil IK (eds) Cell culture in phytochemistry. Cell culture and somatic cell genetics, vol 4. Academic Press, London New York (in press).

    Google Scholar 

  • Yeoman MM, Lindsey K (1985) The scientific and commercial potential of immobilized plant cells. In: Adv Ferment 11:87–92.

    Google Scholar 

  • Yeoman MM, Miedzybrodzka MB, Turrek-Wheatland UK, Lindsey K, McLauchlan WR (1980) The synthetic potential of cultured cells. In: Sala F, Parisi B, Cella P, Ciferri O (eds) Plant cell cultures: Results and perspectives. Elsevier/North Holland Biomedical Press, Amsterdam New York, pp 327–343.

    Google Scholar 

  • Yeoman MM, Lindsey K, Miedzybrodzka MB, McLauchlan WR (1982a) Accumulation of secondary products as a facet of differentiation in plant cell and tissue cultures. In: Yeoman MM, Truman DES (eds) Differentiation in vitro. Univ Press, Cambridge, pp 65–82.

    Google Scholar 

  • Yeoman MM, Lindsey K, Hall RD (1982b) Differentiation as a prerequisite for the production of secondary metabolites. Proc Plant cell culture Conf. Oyez, London, pp 1–7.

    Google Scholar 

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Author notes

  1. R. D. Hall

    Present address: Foundation for Agricultural Plant Breeding, Droevendaalsesteeg 1, 6700, AC Wageningen, The Netherlands

Authors and Affiliations

  1. Department of Botany, University of Edinburgh, Mayfield Road, Edinburgh, EH9 3JH, UK

    R. D. Hall, M. A. Holden & M. M. Yeoman

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  2. M. A. Holden
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  1. A-137, New Friends Colony, New Delhi, 110065, India

    Y. P. S. Bajaj

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Hall, R.D., Holden, M.A., Yeoman, M.M. (1988). Immobilization of Higher Plant Cells. In: Bajaj, Y.P.S. (eds) Medicinal and Aromatic Plants I. Biotechnology in Agriculture and Forestry, vol 4. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-73026-9_6

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