This review provides an informative and broad overview of orchid biotechnology, addressing several important aspects such as molecular systematics, modern breeding, in vitro morphogenesis, protoplast culture, flowering control, flower color, somaclonal variation, orchid mycorrhiza, pathogen resistance, virus diagnosis and production of virus-free plants, functional genomics, genetic transformation, conservation biotechnology and pharmaceutical biotechnology. This resource will provide valuable insight to researchers who are involved in orchid biology and floriculture, using biotechnology to advance research objectives. Producing an improved orchid through biotechnology for industrial purposes or to serve as a model plant for pure and applied sciences is well within reach and many of the current techniques and systems are already employed at the commercial production level.

The Application of Biotechnology to Orchids

Leaf explants of Jatropha curcas cultured on Murashige and Skoog’s (MS) medium supplemented with thidiazuron (TDZ; 0.90 μM) in combination with indole-3-butyric acid (IBA; 0.98μM) produced adventitious shoot buds directly on the surface of the explants without formation of intervening callus while shoot bud formation was accompanied with callus formation on medium supplemented with 6-benzylaminopurine (BAP; 13.3 μM) and IBA (2.46 μM). TDZ treatment resulted in more than twice higher rate of shoot bud induction than BAP. Shoot buds were multiplied and elongated following repeated transfers to medium containing BAP (2.22 μM) and gibberellic acid (GA3; 1.44 μM). The effect of copper sulphate on differentiation of shoot buds from leaf segments was also investigated. Both shoot induction and multiplication media were supplemented with different levels of CuSO4 (0–5 μM). Significant improvement in shoot bud induction was observed when the concentration of CuSO4 was increased to 10 times the normal MS level. Healthy elongated shoots were rooted on half strength MS medium supplemented with IBA (2.46 μM). Rooted plantlets were transferred to field and survived. Histological analysis revealed direct formation of shoot buds from leaf explants.

Direct shoot regeneration from leaf explants of Jatropha curcas in response to thidiazuron and high copper contents in the medium

This article demonstrates the plantlet regeneration from alginate-encapsulated shoot tips of Spilanthes acmella. Shoot tip explants excised from in vitro proliferated shoots were encapsulated in calcium alginate beads. The best gel complexation for encapsulation of shoot tips was achieved using 3% sodium alginate and 100 mM calcium chloride. Maximum percent response for the conversion of encapsulated shoot tips into plantlets was obtained on growth regulator-free full-strength liquid MS (Murashige and Skoog, Physiol Plant 15:473–497, 1962) medium. The addition of MS nutrients in alginate matrix was found to have pronounced effect on shoot and root emergence from alginate beads. Encapsulated shoot tips could be stored at low temperature (4°C) up to 60 days. Plantlets regenerated from encapsulated shoot tips were acclimatized successfully. The present synthetic seed technology could be useful in large-scale propagation as well as short-term conservation and germplasm distribution and exchange of Spilanthes acmella.

Plant regeneration from alginate-encapsulated shoot tips of Spilanthes acmella (L.) Murr., a medicinally important and herbal pesticidal plant species

Plants provide medicine and pest control resources for millions of poor people world-wide. Widespread harvesting of medicinal and pesticidal plants puts pressure on natural populations, thus severely compromising their contribution to the income and well-being of traders and consumers. The development of in vitro propagation techniques appropriate for developing countries will provide a robust platform for effective propagation and cultivation of endangered plants. This review focuses on advances in the application of phytochemical and in vitro tools to identify and rapidly propagate medicinal and pesticidal plants. Problems of over-harvesting can be alleviated and ex situ cultivation in agroforestry systems can be facilitated through improving seed germination, in vitro cloning and the use of mycorrhizal fungi. We also present a case for effective use of phytochemical analyses for the accurate identification of elite materials from wild stands and validation of the desired quality in order to counter loss of efficacy in the long run through selection, propagation or ex situ management in agroforestry systems. Future prospects are discussed in the context of medicinal activity screening, sustainable propagation, on-farm planting, management and utilization.

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Applications of phytochemical and in vitro techniques for reducing over-harvesting of medicinal and pesticidal plants and generating income for the rural poor

Spilanthes acmella, a well known antitoothache plant with high medicinal usages, has been recognized as an important medicinal plant and has an increasingly high demand worldwide. From its traditional uses in health care and food, extensive phytochemical studies have been reported. This review provides an overview and general description of the plant species, bioactive metabolites and important pharmacological activities including the preparation, purification and in vitro large-scale production. Structure-activity relationships of the bioactive compounds have been discussed. Considering data from the literature, it could be demonstrated that S. acmella possesses diverse bioactive properties and immense utilization in medicine, health care, cosmetics and as health supplements. As a health food, it is enriched with high therapeutic value with high potential for further development.

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Review article: HIGH THERAPEUTIC POTENTIAL OF SPILANTHES ACMELLA: A REVIEW

In vitro flowering of Withania somnifera Dunal.—An important antitumor medicinal plant

Multiple shoots of Spilanthes acmella Murr. were induced from nodal buds of in vivo and in vitro seedlings on Murashige and Skoog (MS) medium containing 1.0 mg dm−3 6-benzyladenine (BA) and 0.1 mg dm−3 α-naphthalene-acetic acid (NAA). Adventitious shoots were successfully regenerated from the leaf explants derived from the above mentioned multiple shoots. The efficiency of shoot regeneration was tested in the MS medium containing BA, kinetin, or 2-isopentenyl adenine in combination with NAA, indole-3-acetic acid (IAA), or indole-3-butyric acid (IBA) and gibberellic acid. Maximum number of shoots per explant (20 ± 0.47) was recorded with 3.0 mg dm−3 BA and 1.0 mg dm−3 IAA. An anatomical study confirmed shoot regeneration via direct organogenesis. About 95 % of the in vitro shoots developed roots after transfer to half strength MS medium containing 1.0 mg dm−3 IBA. 95 % of the plantlets were successfully acclimatized and established in soil. The transplanted plantlets showed normal flowering without any morphological variation.

Direct shoot regeneration from leaf explants of Spilanthes acmella

Plants of teak (Tectona grandis L.f.) growing after transplantation to fertile soil for 5 - 6 months were subjected to water stress by withholding watering continuously for 3 weeks. The growth rates of both plants in height and developing leaves in length were unaffected during the first week after withholding watering, but they were decreased by about 50 % during the second week and became negligible during the third week of water stress treatment. The rate of leaf production and internodal elongation were also decreased in plants experienced 2 weeks of water stress. However, after rewatering, these plants regained growth potential and exhibited high rates of leaf expansion and plant growth comparable to those of well-watered plants. Diurnal course of net photosynthetic rate (PN) of plants subjected to water stress for 2 weeks was similar as that of well-watered plants. However, PN of plants subjected to water stress for 3 weeks was reduced in the afternoon. Similarly, stomatal conductance (gs) and transpiration rate (E) of plants experiencing 3-week water stress were decreased in the afternoon. Soon after rewatering, PN, gs and E reached similar values to those of well-watered plants.

Effects of water stress on leaf growth and photosynthetic and transpiration rates of Tectona grandis

Net photosynthetic rate (PN), ribulose-1,5-bisphosphate carboxylase (RuBPC) activity, chlorophyll (Chl) content and biomass production were estimated at monthly intervals inChukrasia tabularis, Dolichandrone atrovirens, Eugenia jambolana, Gmelina arborea, Lannea coromandelica, Terminalia arjuna andTerminalia bellerica from September 1990 to August 1991. The leaves of all the seven tree species showed significantly higher PN during summer than in winter and these rates differed from one species to the other. A positive correlation was found between PN of different tree species and their Chl content or biomass production. There was no significant correlation between ribulose-1,5-bisphosphate carboxylase activity and PN when these were expressed on leaf area basis.

Seasonal pattern of photosynthetic rate and its relationship with chlorophyll content, ribulose-1,5-bisphosphate carboxylase activity and biomass production

C. V. Naidu

Papers

In vitro flowering of Withania somnifera Dunal.—An important antitumor medicinal plant

Direct shoot regeneration from leaf explants of Spilanthes acmella

Effects of water stress on leaf growth and photosynthetic and transpiration rates of Tectona grandis

Seasonal pattern of photosynthetic rate and its relationship with chlorophyll content, ribulose-1,5-bisphosphate carboxylase activity and biomass production