in vitro propagation – a potential method for plant conservation

7/27/2019 IN VITRO PROPAGATION A POTENTIAL METHOD FOR PLANT CONSERVATION

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Volume: 02, October 2013, Pages: 268-272 International Journal of Computing Algorithm

Integrated Intelligent Research (IIR) 268

IN VITRO PROPAGATION A POTENTIAL METHOD FOR PLANTCONSERVATION

A.Vinoth, R.Ravindhran

Department of Plant Biology and Biotechnology, Loyola College, Chennai -600034, [email protected]

Abstract

Conservation of plant biodiversity, a potential resource for health care, is essential for the verysurvival of the human race. Increasing importance to traditional medicine in the recent years hasthreatened the survival of rare species. Conventional plant propagation methods are affected byvariable environmental factors and time consuming. In vitro propagation, an ex situ conservationstrategy, provides new means for conservation and mass propagation of economically important

plants. In addition, in vitro plant systems serve as an alternative approach for the production of bioactive compounds from medicinal plants. The present review is to focus on application of in vitro

propagation via organogenesis, somatic embryogenesis and cell suspension culture for plant conservation.Keywords : Micropropagation, Synthetic seeds, Secondary metabolites, Germplasm conservation

1. IntroductionPlant genetic resources are a vital part of theworlds biological diversity and an essentialsource for the human well being. Plants play akey role in maintaining the environmental

balance and ecosystem stability and provide animportant component of the habitats for theworld's animal life. In addition to the crop

plants that provide us food, many thousands of wild plants have great economic and culturalimportance and potential for use in traditionalmedicines throughout the world. However, theworlds biodiversity is declining at anunprecedented rate due to the alarmingincrease in the world population and many

plants are in danger of extinction, threatened by habitat transformation, over-exploitation,unsustainable agriculture and forestry

practices, alien invasive species, pollution and climate change. Hence the loss of biodiversityin large scale in the recent years has set one of the greatest challenges for the world community, that is, to halt the destruction of the plant diversity to meet the present and future needs of humankind.The Global Strategy for Plant Conservationhas been adopted unanimously at the sixth

meeting of the Conference of the Parties to theConvention on Biological Diverstiy (CBD)

held at Hague in April, 2002 to address thechallenge of biodiversity conservation. Thisstrategy aims to improve long-termconservation, management and restoration of

plant diversity, plant communities, and theassociated habitats and ecosystems both in situ (in natural habitats) and ex situ . Althoughspecies conservation is achieved mosteffectively through the management of wild

populations and natural habitats ( in situ conservation), ex situ conservation methodshave been favourably used to complement insitu measures and, in some instances, may bethe only option for some species [1-2]. Theimportance of ex situ conservation has gained international recognition with its inclusion inArticle 9 of the Convention on BiologicalDiversity (CBD) [3] and in Target 8 of theGlobal Strategy for Plant Conservation(www.bgci.org.uk/files/7/0/global_strategy.pd f).Approaches to ex situ conservation includemethods like seed storage, field genebanks and

botanical gardens. DNA and pollen storagealso contribute indirectly to ex situ conservation of plant genetic resources.Among the various ex situ conservation

methods, seed storage is the most convenientfor long-term conservation of plant genetic


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resources. However, conventional seed storagestrategies are not possible for a large number of important tropical and sub-tropical treespecies which produce recalcitrant seeds thatquickly lose viability and do not survivedesiccation [4]. Field genebanks provide easyaccess to conserved material but they run therisk of destruction by natural calamities, pestsand diseases. Hence, in vitro conservationoptions through tissue culture techniques have

been the safest alternative with several distinctadvantages for plant conservation. In vitro techniques have been found to be useful in the

propagation of a large number of threatened plants [5-6] and the Micropropagation Unit at

Royal Botanical Gardens, Kew has beeninvolved in the propagation and maintenanceof more than 3000 plant taxa, from all over theworld, for over 30 years. In addition, cellsuspension culture systems could be used for large scale culturing of plant cells from whichsecondary metabolites could be extracted. Thismethod ultimately provides a continuous and reliable source of natural products.Thus the present review aims to highlight the

importance of in vitro propagation methods in plant conservation. Development of techniquesfor conservation, with special emphasis onmicropropagation, somatic embryogenesis and cell suspension cultures using both threatened and non-threatened plants are discussed.

2. In vitro propagation techniques2.1. MicropropagationMicropropagation involves the production of

plants using shoot tip or nodal culture. In thistechnique, newly formed shoots or shoot basesserve as explants for repeated proliferation of

plants. Micropropagation plays a distinctiverole in the conservation of species, particularlythose having pharmacologic value [7]. It offerscost-effective protocols for large scale

propagation of medicinal plants collected fromthe wild without affecting the survival of thespecies in their natural habitats [8]. Thelaboratory at Kings Park & Botanic Garden,Perth, Australia (http://www.kpbg.wa.gov.au)specialized in the conservation of threatened

flora of Western Australia has developed techniques for the micropropagation of over 200 species representing 33 families of Australian plants. The Tropical BotanicGardens and Research Institute in Kerala,India has studied the in vitro conservation of 46 medicinal plants and 30 orchids from theconservation hotspot of Western Ghats(www.tbgri.org).Micropropagation helps to improve medicinal

plants through the selection of high-yield linesand their efficient cloning. Genetically similar clones of Talinum triangulare , a medicinalherb, were obtained through micropropagation[9]. The most significant advantage offered by

this aseptic method of clonal propagation over the conventional methods is that in a relativelyshort time and space, a large number of plantscan be produced starting from a singleindividual. For orchids, micropropagation isthe only commercially viable method of clonal

propagation. Over 250 orchid genera have been successfully propagated at RoyalBotanical Gardens, Kew including speciesfrom Angraecum, Paphiopedilum,

Phragmipedium , and Cypripedium , many of which are threatened in the wild [10].Micropropagation allows for the creation and dissemination of large numbers of nursery

plants without spreading pathogens acrosscontinents. It has been of great help in large-scale production of disease-free plantingmaterials of elite Vanilla planifolia genotypes[11].In the past decade, autotrophicmicropropagation, an in vitro culture without acarbon source has gained importance in the

propagation of economically important plants.In comparison with plantlets produced byconventional micropropagation systems, those

produced by photoautotrophic systems with asugar-free medium showed better growth,higher quality, lower contamination rate invitro , and higher percentage survival ex vitro [12-13]. This method is still under laboratorytrials and if good multiplication rates areachieved, this method should be explored togenerate quality plants for reintroduction and long-term conservation of threatened species.


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2.2. Somatic embryogenesisSomatic embryogenesis is the techniqueinvolving the formation of embryo-likestructures in plant cultures without the act of fertilization. Embryos thus formed in culturesand variously designated as accessoryembryos, adventive embryos, embryoids or supernumerary embryos have the potential todevelop into whole plants without theapplication of plant growth regulators in theculture medium. The first observations of invitro somatic embryogenesis were made asearly as 1950s in Daucus carota [14-16].Although somatic embryos serve as a modelsystem in embryological studies, the greatest

interest lies in the practical application for large-scale vegetative propagation, especiallythrough scale up of the propagation using

bioreactors [17]. It has also been suggested that regeneration via embryogenesis has better chances of obtaining genetically uniform

plants than through organogenicdifferentiation [18].Another approach to the plant regeneration viasomatic embryogenesis is the production of

synthetic seeds or syn seeds. In this method,naked embryos are encapsulated in a

protective covering which not only protectsthe embryo but also provides nutrients for germination thus resembling the true seeds.Thus, somatic embryogenesis is potentially themost amenable system to automation, not onlyat the production stage but also for mechanized planting in the field as syntheticseeds [19-20]. In most cases, somatic embryosor embryogenic cultures can be cryopreserved,which makes it possible to establish gene

banks.2.3. Cell suspension culturesCell suspension culture is the process of culturing of cells or cell aggregates in anagitated liquid medium. Plant cell bioreactor technology promises exploitation of the plantkingdom as a rich resource of important and unique specialty chemicals [21]. Plant cell

bioreactors also provide favorable conditionsfor improved secondary metabolite formation.Vast numbers of secondary metabolites have

been produced using cell suspension culturesin the recent years. Calli and cell suspensionsof different species of Linum, Callitris and Podophyllum [22-28] have been reported assources of aryltetralin lignans. Suspensionculture systems have been established for the

production of caffeic acid derivatives (CAD)from Echinacea purpurea [29-30], flavonoid from Saussurea medusa [31-32] and gymnemic acid from Gymnema sylvestre [33].Protoplasts isolated from embryogenicsuspensions, may give rise to somatic embryosdirectly, without any intervening callus phase[34-35]. Cryopreservation for high-frequency

plant regeneration via somatic embryogenesis

has been achieved from zygotic embryo-derived cell suspension cultures of Ranunculuskazusensis [36]. Though this technique is notsufficiently reliable for plant propagation, it isthe best method available for the production of medicinally important compounds from plantspecies, thereby facilitating their sustainableutilization.

3. Conclusion

In vitro propagation has a great potential for germplasm conservation of plant geneticresources. Ex situ conservation using in vitro methods provides a safe repository for plant

populations derived from severely at risk locations. In vitro regeneration systems favour rapid production of large numbers of plantlets,without seasonal dependency, for ex situ commercial cultivation purposes and reducesthe risk of endangered plants being sampled from wild habitats thus safeguarding theexisting natural populations. In vitro

propagated plants may also be acclimatized tonatural environments and utilized in controlled

breeding programmes for seed production.Hence in vitro propagation methods are notonly an alternative means for mass

proliferation of plants but also help in theconservation of endangered plant species.

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in vitro propagation – a potential method for plant conservation

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