The origin of plant cell and tissue culture can be found in a treatise published during the mid-18th century, entitled La Physique des Arbes, that describes the formation of callus tissue following the for mation of a ring of cortex from elm trees. Over the next two centuries, the discovery of plant growth hormones, in particular auxins and cytokinins, and detailed analyses on the nutritional requirements of plants, led to the formulation of media that could maintain actively dividing cultures derived from gymnosperms, and both dicotyledon ous and monocotyledonous angiosperms. However, much of the prog ress and technological development in the in vitro propagation of plant cells, tissues, and organs has occurred during the last 25 years. Recently, plant tissue culture techniques have been used as basic tools in the rapidly expanding field of plant biotechnology for the development and clonal propagation of new and/or improved plant varieties. Plant tissue culture is used for the micropropagation of commercially valuable cultivars that include ornamentals, oil palm, Glycyrrhiza, Pyrethrum, pine, Eucalyptus, sugar cane, and potatoes. Cultured plant tissue is also used for the selection of cells and, ul timately, the regeneration of plants that are tolerant to physical stresses such as pathogens, drought, and temperature extremes, and to chemical stress agents such as salinity, herbicides, proteins, and pyrethrins. In addition, new plants have been produced by the fusion of protoplasts prepared from cultured cells of different species in cluding sunflower and french bean, tomato and potato, and various cultivars of Datura. Finally, bacterial vectors and various mechanical methods have been used to introduce foreign genes into cultured plant tissues. Genetic transformation can result in profound changes in the phenotype and/or biochemical profile of the regenerated trans genic plants that are not characteristic of the wild type. An impressive variety of technologies in tissue culture, genetic manipulation, and molecular biology have been developed for nu merous plant species. Many of these techniques, sometimes referred to as plant biotechnology, have been extensively summarized and compiled in a well-balanced collection of easy-to-follow protocols presented in three separate, but complimentary, volumes. Plant Cell, Tissue and Organ Culture consists of 22 chapters (with 86 figures) and 5 appendices. The chapters cover critical aspects of (a) the es sential requirements for the operation of a plant tissue culture lab oratory; (b) the basic procedures of micropropagation, regeneration, and somatic embryogenesis; (c) some specific applications of organ culture systems such as embryo rescue and culture, and anther and microspore culture for haploid and double haploid production; (d) elementary transformation technology; and (e) useful microtechnique and analytical protocols specifically adapted to cultured tissues and cells. The appendices provide a convenient summary of media for mulations and commercial suppliers for the materials described in the text.

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Plant Cell, Tissue and Organ Culture

Mangroves are woody plants which form the dominant vegetation in tidal, saline wetlands along tropical and subtropical coasts. The current knowledge concerning the most striking feature of mangroves i.e., their unique ability to tolerate high salinity is summarized in the present review. In this review, we shall discuss recent studies that have focused on morphological, anatomical, physiological, biochemical, molecular and genetic attributes associated with the response to salinity, some of which presumably function to mediate salt tolerance in the mangroves. Here we shall also review the major advances recently made at both the genetic and the genomic levels in mangroves. Salinity tolerance in mangroves depends on a range of adaptations, including ion compartmentation, osmoregulation, selective transport and uptake of ions, maintenance of a balance between the supply of ions to the shoot, and capacity to accommodate the salt influx. The tolerance of mangroves to a high saline environment is also tightly linked to the regulation of gene expression. By integrating the information from mangroves and performing comparisons among species of mangroves and non-mangroves, we could give a general picture of salt tolerance mechanisms of mangroves, thus providing a new avenue for development of salt tolerance in crop plants through effective breeding strategies and genetic engineering techniques.

Salt tolerance mechanisms in mangroves: a review

This long-awaited book would seem to mark the end of classical tropical botany and phytogeography as subjects for scholarly pursuits. Since the middle of the century, when the first edition of The Tropical Rain Forest appeared, the wet tropical lowlands of the world have become an industrial battleground and, today at the end of the "Second Millennium", the future of the remaining rainforests that have evolved over millions of years looks bleak. Indeed, the book may well become "a record of what the rainforest was like in the twentieth century", as stated on its first page. This elegiac declaration not only reflects world concern about its pending extinction, but also Professor Richards' increasingly personal involvement with rainforest conservation in his later years.

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The Tropical Rain Forest: An Ecological Study

The advancements made in tissue culture techniques has made it possible to regenerate various horticultural species in vitro as micropropagation protocols for commercial scale multiplication are available for a wide range of crops. Clonal propagation and preservation of elite genotypes, selected for their superior characteristics, require high degree of genetic uniformity amongst the regenerated plants. However, plant tissue culture may generate genetic variability, i.e., somaclonal variations as a result of gene mutation or changes in epigenetic marks. The occurrence of subtle somaclonal variation is a drawback for both in vitro cloning as well as germplasm preservation. Therefore, it is of immense significance to assure the genetic uniformity of in vitro raised plants at an early stage. Several strategies have been followed to ascertain the genetic fidelity of the in vitro raised progenies comprising morpho-physiological, biochemical, cytological and DNA-based molecular markers approaches. Somaclonal variation can pose a serious problem in any micropropagation program, where it is highly desirable to produce true-to-type plant material. On the other hand, somaclonal variation has provided a new and alternative tool to the breeders for obtaining genetic variability relatively rapidly and without sophisticated technology in horticultural crops, which are either difficult to breed or have narrow genetic base. In the present paper, sources of variations induced during tissue culture cycle and strategies to ascertain and confirm genetic fidelity in a variety of in vitro raised plantlets and potential application of variants in horticultural crop improvement are reviewed.

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Somaclonal variations and their applications in horticultural crops improvement

Pongamia pinnata (L.) Pierre is a fast-growing leguminous tree with the potential for high oil seed production and the added benefit of the ability to grow on marginal land. These properties support the suitability of this plant for large-scale vegetable oil production required by a sustainable biodiesel industry. The future success of P. pinnata as a sustainable source of feedstock for the biofuels industry is dependent on an extensive knowledge of the genetics, physiology and propagation of this legume. In particular, research should be targeted to maximizing plant growth as it relates to oil biosynthesis. This review assesses and integrates the biological, chemical and genetic attributes of the plant, providing the basis for future research into Pongamia’s role in an emerging industry.

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Pongamia pinnata: an untapped resource for the biofuels industry of the future.

Ginger (Zingiber officinale Roscoe) is an economically important plant, valued all over the world. The existing variation among 16 promising cultivars as observed through differential rhizome yield (181.9 to 477.3 g) was proved to have a genetic basis using different genetic markers such as karyotype, 4C nuclear DNA content and random amplified polymorphic DNA (RAPD). The karyotypic analysis revealed a differential distribution of A, B, C, D and E type of chromosomes among different cultivars as represented by different karyotype formulas. A significant variation of 4C DNA content was recorded in ginger at an intraspecific level with values ranging from 17.1 to 24.3 pg. RAPD analysis revealed a differential polymorphism of DNA showing a number of polymorphic bands ranging from 26 to 70 among 16 cultivars. The RAPD primers OPC02, OPA02, OPD20 and OPN06 showing strong resolving power were able to distinguish all 16 cultivars. The extent of genetic diversity among these cultivars was computed through parameters of gene diversity, sum of allele numbers per locus and Shannon's information indices. Cluster analysis, Nei's genetic similarity and genetic distances, distribution of cultivars into special distance classes and principal coordinate analysis and the analysis of molecular variance suggested a conspicuous genetic diversity among different cultivars studied. The genetic variation thus detected among promising cultivars of ginger has significance for ginger improvement programs.

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Assessment of genetic diversity among 16 promising cultivars of ginger using cytological and molecular markers.

An efficient large-scale clonal propagation protocol has been described for Withania somnifera (L.) Dunal, a valuable medicinal plant, using cotyledonary nodes derived from axenic seedlings. Murashige and Skoog’s (Physiol Plant 15:473–497, 1962) (MS) medium supplemented with 1.0 mg l−1N6-benzyladenine (BA) was found to be optimum for production of multiple shoots (100 % shoot proliferation frequency and 16.93 shoots per explant). Successive shoot cultures were established by repeatedly sub-culturing the original cotyledonary node on a fresh medium after each harvest of newly formed shoots. Multiple shoot proliferation was also achieved from nodal segments derived from in vitro raised shoots on MS medium augmented with 1.0 mg l−1 BA. Regenerated shoots were best rooted (95.2 %, 38.7 roots per shoot) in half-strength MS medium supplemented with 1.0 mg l−1 indole-3-butyric acid. The plantlets were successfully acclimated and established in soil. Random amplified polymorphic DNA and inter-simple sequence repeats analysis revealed a homogeneous amplification profile for all micropropagated plants analyzed validating the genetic fidelity of the in vitro regenerated plants.

In vitro plant regeneration from cotyledonary nodes of Withania somnifera (L.) Dunal and assessment of clonal fidelity using RAPD and ISSR markers

was developed for in vitro propagation of an elite genotype of Curcuma longa (cv Roma) using axillary buds from unsprouted rhizomes. The explant produced multiple shoots when cultured on MS basal medium supplemented with varying combinations and concentrations of Benzyladenine, Kinetin,α Napthalene, Acetic acid, Indole-3- acetic acid and Adenine sulphate. Medium containing BA (3mg/l) was found to be optimum for micropropagation and conservation of C. longa plantlets. The genetic stability of the micropropagated clones was evaluated over 26 months in culture using cytophotometry and Random Amplified Polymorphic DNA (RAPD) analysis. Cytophotometry analysis revealed unimodal DNA distribution with 4C peak and RAPD analysis revealed monomorphic bands in all in vitro grown plants of C. longa, thus confirming genetic uniformity among somaclones of C. longa. This study is of high significance as these cultures are currently being used as source of disease free planting material for commercial utilization.

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Assessment of genetic stability of micropropagated plants of Curcuma longa L. by cytophotometry and RAPD analyses

Rhizome yield, 4C nuclear DNA content and RAPD analysis were carried out of 17 promising cultivars of turmeric (Curcuma longa L.). The rhizome yield per plant varied significantly from 77.66 to 350 g among 17 cultivars of Curcuma longa. Significant variation of 4C DNA content was recorded at the intraspecific level with values ranging from 4.30 to 8.84 pg. The differential DNA content observed among 17 different cultivars of Curcuma longa comprising same (2n=48) chromosome number could be attributed to the loss or addition of highly repetitive sequences in the genome. Random amplified polymorphic DNA (RAPD) analysis clearly revealed genetic variation among 17 cultivars of turmeric showing differential polymorphism using 20 primers. The amplification fragments per primer ranged from 4 to 17 in 17 cultivars with fragment size ranging from 0.4 kb to 3 kb. Intraspecific polymorphism ranged from 35.6% to 98.6% among 17 cultivars studied. The RAPD primers OPN06 and OPA04 having strong resolving power were able to distinguish all 17 cultivars. The extent of genetic diversity among 17 cultivars was computed through Nei's genetic similarity and genetic distances. The genetic variations detected through 4C nuclear DNA content and RAPD analysis have significance for turmeric improvement programmes.

Detection and Evaluation of Genetic Variation in 17 Promising Cultivars of Turmeric (Curcuma longa L.) Using 4C Nuclear DNA Content and RAPD Markers

Genetic diversity was evaluated among 14 cultivars of Catharanthus roseus using RAPD and ISSR markers. The RAPD primers resulted in the amplification of 56 bands, among which 46 (82%) bands were polymorphic Four ISSR primers amplified 31 loci out of which 17 were polymorphic and 14 are monomorphic. The Jaccard's similarity derived from the combined marker system showed that the varieties First Kiss Coral and Cooler Orchid were the most closely related cultivars, with 98% similarity. In the dendrogram constructed on the basis of both RAPD and ISSR data two clear clusters were obtained. The smaller cluster included C. roseus Cv Blue Pearl and C. roseus Cv. Patricia White and the larger cluster was subdivided into two sub clusters with C. roseus Cv. First Kiss Polka Dot isolated from the rest of the cultivars. This may be useful for breeding for improved quality.

Laxmikanta Acharya

Papers

Assessment of genetic diversity among 16 promising cultivars of ginger using cytological and molecular markers.

In vitro plant regeneration from cotyledonary nodes of Withania somnifera (L.) Dunal and assessment of clonal fidelity using RAPD and ISSR markers

Assessment of genetic stability of micropropagated plants of Curcuma longa L. by cytophotometry and RAPD analyses

Detection and Evaluation of Genetic Variation in 17 Promising Cultivars of Turmeric (Curcuma longa L.) Using 4C Nuclear DNA Content and RAPD Markers

Assessment of genetic diversity in a highly valuable medicinal plant Catharanthus roseus using molecular markers.