The classical observations of the skin as a target for melanotropins have been complemented by the discovery of their actual production at the local level. In fact, all of the elements controlling the activity of the hypothalamus-pituitary-adrenal axis are expressed in the skin including CRH, urocortin, and POMC, with its products ACTH, α-MSH, and β-endorphin. Demonstration of the corresponding receptors in the same cells suggests para- or autocrine mechanisms of action. These findings, together with the demonstration of cutaneous production of numerous other hormones including vitamin D3, PTH-related protein (PTHrP), catecholamines, and acetylcholine that share regulation by environmental stressors such as UV light, underlie a role for these agents in the skin response to stress. The endocrine mediators with their receptors are organized into dermal and epidermal units that allow precise control of their activity in a field-restricted manner. The skin neuroendocrine system communicates with itself and wi...

Neuroendocrinology of the skin.

In vitro manipulation and propagation of medicinal plants

The broad applications of somatic embryogenesis, both in basic and applied research, have stimulated studies on the determination of in vitro conditions for the induction of somatic embryos and their conversion into plants. As a result, efficient protocols on SE induction and plant regeneration have recently become available for many plant species, including Arabidopsis thaliana (L.) Heynh., a model plant in genetics and embryogenesis. Studies on factors controlling in vitro plant morphogenesis are highly desirable not only for the development of improved regeneration systems, but also for the analysis of molecular mechanisms underlying plant embryogenesis. This review focuses on the conditions influencing the induction of embryogenic potential in in vitro cultured plant cells. The roles of explant type, endo- and exogenous plant growth regulators and stress factors in the induction of somatic embryogenesis are especially emphasized. Possible mechanisms by which different factors induce or modify embryogenic competence in cultured plant cells are also discussed. Since the production of genetically solid and true-to-type plants is desired, especially for transformation and micropropagation practice, the problem of the genetic characteristics of regenerants, in terms of their chimerism and somaclonal variation, is discussed in some detail. Special consideration is given to A. thaliana– a major model plant species for classical genetics and genomics. Recent availability of efficient embryogenic cultures in this organism makes it possible to benefit from advanced genomic research of Arabidopsis to study plant embryogenesis on the molecular level.

Factors influencing somatic embryogenesis induction and plant regeneration with particular reference to Arabidopsis thaliana (L.) Heynh

Medicinal plants are the most important source of life saving drugs for the majority of the world's population. The biotechnological tools are important to select, multiply and conserve the critical genotypes of medicinal plants. In-vitro regeneration holds tremendous potential for the production of high-quality plant-based medicine. 
Cryopreservation is long-term conservation method in liquid nitrogen and provides an opportunity for conservation of endangered medicinal plants. In-vitro production of secondary metabolites in plant cell suspension cultures has been reported from various medicinal plants. Bioreactors are the key step towards commercial production of secondary metabolites by plant biotechnology. Genetic transformation may be a powerful tool for enhancing the productivity of novel secondary metabolites; especially by Agrobacterium rhizogenes induced hairy roots. This article discusses the applications of biotechnology for regeneration and genetic transformation for enhancement of secondary metabolite production in-vitro from medicinal plants. Key words: Bioreactors; genetic transformation; regeneration; secondary metabolites 
Abbreviations: BA: 6-Benzylaminopurine; TDZ: 1-Phenyl-3-(1,2,3-thiadiazol-5-yl) urea; NAA: a-Naphthaleneacetic acid; IAA: Indole-3 acetic acid; 2iP: 6-(g-Dimethylallylamino) purine; 2,4-D: 2,4-Dichlorophenoxyacetic acid; GA3: Gibberellic acid Trop J Pharm Res , December 2003; 2(2): 243-253

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Role of biotechnology in medicinal plants

In vitro propagation of rose--a review.

Somatic embryogenesis and plant regeneration were obtained from immature leaflet callus of chickpea. Numerous globular embryos developed on the surface of callus on Murashige and Skoog's (1962) medium containing 25 μM 2,4-dichlorophenoxyacetic acid. These globular embryos differentiated into mature somatic embryos upon removal of 2,4-dichlorophenoxyacetic acid. The maturation of embryos was significantly affected by pH, photoperiod, abscisic acid and genotype. Callus continued to produce somatic embryos for over 8 subcultures at 4 week intervals. Two per cent of the embryos formed plants on medium containing 15 μM gibberellic acid and 1 μM indole-3-butyric acid. Desiccation of embryos for a period of 3 d increased their rate of conversion into plants from 0.9 to 2.8%. All regenerated plants showed normal morphological characteristics.

Somatic embryogenesis and plant regeneration from callus cultures of chickpea (Cicer arietinum L.).

Plantlets of the mulberry (Morus alba L. vars. Chinese White, and Kokuso-27) were produced from callus cultures. For callus induction, leaf, internodal segments, and petiole explants of Chinese White, Kokuso-27 and Ichinose varieties were grown on MS basal medium fortified with 2,4-D and 6-benzylaminopurine (BA). Callogenesis was dependent on the nature of explant used, the genotype and growth regulators supplemented in the medium. Leaves were the best explant type used for callus induction. Best callogenesis was obtained on MS medium containing a combination of 1 mg l−1 2,4-D and 0.5 mg l−1 BA (95-100%). Calluses formed shoots on MS medium supplemented with 1 mg l−1 BA. Supplementation with 0.1 mg l−1 2,3,5-triiodobenzoic acid (TIBA) in this medium enhanced shooting response. Presence of TIBA in the medium also improved the long-term organogenic potential of the callus. Regenerated shoots produced roots on Murashige & Skoog (MS) medium containing either 0.5 mg l−1 indole-3-butyric acid (IBA) or α-naphthaleneacetic acid (NAA). Seventy percent of the rooted plants were established in the field where they are performing well.

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Effect of genotype, explant type and growth regulators on organogenesis in Morus alba

A protocol for whole plant regeneration of Cicer arietinum L. cv. C-235 via organogenesis from callus has been developed. Callus initiation was best when immature leaflets were cultured on MS medium containing 5 or 25 μM 2,4-D or NAA in combination with 10 μM BA, or 25 μM 2,4-D alone. The callus grew most vigorously on MS medum supplemented with 10 μM NAA and 5 μMBA. Best shoot differentiation was obtained from calli derived from the basal portion of shoot tips on MS medium supplemented with 10 μM BA and 0.1 μM IBA. The shoot forming ability of calli was enhanced by adding 5 mM potassium phosphate to the medium. Shoots were rooted on a MS medium containing l μM IBA. The regenerated plants were grown to maturity and produced viable seed.

Whole plant regeneration of Cicer arietinum from callus cultures via organogenesis.

The technique for callus initiation, growth and plant regeneration from cultured hypocotyl explants of Plantago ovata cv. GI-2 is described. Best initiation and growth of callus was achieved on Murashige & Skoog's medium containing 2,4-dichlorophenoxyacetic acid (1.0 mgl-1) and kinetin (1.0 mgl-1). The callus showed maximum shoot differentiation on medium containing kinetin (4.0 mgl-1) and α-naphthaleneacetic acid (0.01 mgl-1). Root formation of shoots was best on half-strength medium supplemented with 3-indolebutyric acid. The regenerated plants were successfully transferred into pots.

Callus initiation, growth and plant regeneration in Plantago ovata Forsk. cv. GI-2

Callus was obtained from mericarps of Bunium persicum Boiss. on MS medium supplemented with 2.0 mg/1 2,4-D and 4.0 mg/1 Kn. Small white clumps of compactly packed cells developed on the callus on a medium containing 1.0 mg/1 2,4-D and 0 mg/1 Kn. These cell clumps differentiated numerous globular embryos on the same medium. Embryo maturation and germination was achieved on the basal as well as on 1 mg/1 Kn supplemented medium. All regenerated plants examined were normal diploids with 2n=14.

A. K. Wakhlu

Papers

Somatic embryogenesis and plant regeneration from callus cultures of chickpea (Cicer arietinum L.).

Effect of genotype, explant type and growth regulators on organogenesis in Morus alba

Whole plant regeneration of Cicer arietinum from callus cultures via organogenesis.

Callus initiation, growth and plant regeneration in Plantago ovata Forsk. cv. GI-2

Somatic embryogenesis and plant regeneration from callus cultures of Bunium persicum Boiss.