Tissue Culture Approaches in Relation to Medicinal Plant Improvement

Abstract

The medicinal and aromatic plant species owe their importance to the production of secondary metabolites. These species with worldwide highest volume of business for phytopharmaceuticals, herbal supplements and functional food ordered by size are ginseng (Panax ginseng C.A. Mey.), ginkgo or maidenhair tree (Ginkgo biloba L.), noni or Indian mulberry (Morinda citrifolia L.), saw palmetto (Serenoa repens [W. Bartram] Small), coneflower (Echinacea spp. Moench), valerian or all-heal (Valeriana officinalis L.), green tea (Camellia sinensis [L.] Kuntze), garlic (Allium sativum L.), Saint John’s wort (Hypericum perforatum L.), black cohosh, black snakeroot (Actaea racemosa L., syn. Cimicifuga racemosa [L.] Nutt.), great nettle (Urtica dioica L.), horse chestnut (Aesculus hippocastanum L.), hawthorn (Crataegus spp.) and apricot vine or maypop (Passiflora incarnata L.) (Hoppe (2013) Handbuch des Arznei- und Gewürzpflanzenbaus (book in German), vol 1. Saluplanta, Bernburg, pp 509–513). Plant tissue and protoplast culture/somatic hybridization methods offer a huge scope for creation and conservation of genetic variability for the improvement of a wide variety of medicinal plants. In addition to this, tissue culture methods are now being used for the production of secondary metabolites in vitro. The micropropagation is the best example of the commercial application of tissue culture technology. Meristem-tip culture helps in developing disease-free plants. Development of efficient methods for somatic embryogenesis and embryo desiccation and encapsulation technology may lead to the production of ‘synthetic seeds’ for mass cloning of plants. Somatic embryogenesis in plants further helps in cloning and genetic transformation. Production of haploids anther/pollen culture from wide hybrids has been exploited for the early release of varieties. Embryo culture is very useful technique to obtain interspecific and intergeneric hybrids among otherwise difficult to cross parents. Protoplast culture and somatic cell hybridization help in combining characteristics even from otherwise sexually incompatible plant species and to obtain cytoplasmic hybrids (cybrids). In vitro freeze-storage and cryopreservation in liquid nitrogen at ultra-low temperature of –196 °C (−320 °F) are very important methods for germplasm conservation especially of the vegetatively propagated crops. Since the possibility of producing useful secondary products in plant cell cultures was first recognized in the 1970s, significant progress has been made, and a number of plant species have been found to produce secondary products such as capsaicin, shikonin, diosgenin, caffeine, glutathione and anthraquinone.