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Minichromosomes: The second generation genetic engineering tool

Aakash Goyal, Pankaj Kumar Bhowmik and Saikat Kumar Basu*

Abstract

Genetic engineering is a scientific tool used in every field of science like plant, animal and human sciences. Plant genetic engineering technology has changed the face of plant sciences and the first generation of transgenic crops has become the most rapidly adopted technology in modern agriculture. But genetic engineering has some limitations and therefore still there is a clear need of new technologies to overcome issues like gene stacking, transgene position effects and insertion-site complexity. The recent strategy that researchers have developed to overcome those limitations is the development of plant artificial minichromosomes for delivery of large DNA sequences, including large genes, multigene complexes, or even complete metabolic pathways. A minichromosome is an extremely small version of a chromosome that have been produced by de novo construction using cloned components of chromosomes or through telomere-mediated truncation of endogenous chromosomes. After a successful experiment in maize with the help of minichromsomes by J. Birchler and colleagues (Yu et al., 2007a), a new paradigm have been set for all the agricultural researchers to use the minichromosome techniques for crop improvement. Engineered minichromosomes also offer an enormous opportunity to improve crop performance, as discussed by Houben and Schubert (2007). With rapidly expanding research in minichromosome as a second generation genetic engineering tool we can hope that it will bring a new generation of improved crop species to meet the global demands.

Keywords: Arabidopsis; B chromosomes; maize; mini B chromosome; minichromosomes

(Pages 1-8) PDF full text

Screening wheat germplasm for heat tolerance at terminal growth stage

Aziz ur Rehman, Imran Habib, Nadeem Ahmad, Mumtaz Hussain, M. Arif Khan, Jehanzeb Farooq and Muammad Amjad Ali*

Abstract

The germplasm comprising of 442 wheat varieties/lines was sown in one meter long row in a plastic sheet tunnel to screen the material for heat tolerance during 2004-05 and 2005-06 at Wheat Research Institute, Faisalabad. A set of the material was sown in the open adjacent to the tunnel. The material was exposed to heat shock (>320C) by covering the tunnel with plastic sheet during grain formation for two weeks in 2004-05 and for four weeks in 2005-06. Data was recorded from 25 randomly selected heads from each row for 1000 grain weight, grains per spike and yield per spike during both the years. The data regarding survival (ability to stay green under heat stress) was also recorded. Heat effect was expressed as ratio of stressed / non stressed plants. The effects of heat stress were lesser in shorter period exposure and more drastic in prolonged exposure of the genotypes to heat. The ability of lines to stay green for longer period in heat shock had no direct relationship with seed setting.   Three entries CB-367 (BB#2/ PT// CC/ INIA /3/ ALD’S’) CB-333 (WL 711/3/KAL/BB//ALD ‘S’) and CB-335 (WL711/CROW ‘S’//ALD#1/CMH 77A. 917/3/HI 666/PVN ‘S’ ) showed maximum grain development and survival. This study revealed that these genotypes can be utilized in breeding programs for development of wheat varieties having heat tolerance at terminal growth stage.

Keywords: Bread wheat; Germplasm; Tunnel; Heat stress; Survival


(Pages 9-19) PDF Full text

Genetic diversity analysis in Cymbopogon species using DNA markers

*J. Kumar, V. Verma, A. Goyal, A.K. Shahi, R. Sparoo, R. S. Sangwan and G.N. Qazi1

Abstract

Genetic diversity of 25 accessions of Cymbopogon aromatic grasses including eight species, two hybrids and one mutant strain were analyzed using DNA markers generated by employing 20 primer pairs derived from cDNAs containing simple sequence repeat (SSR) of rice genome. A total of 151 bands were produced ranging from 3 to 12 per primer pair. The polymorphic information content values varied from 0.143 to 0.916 with an average 0.715. Jaccard’s similarity coefficient ranged from 64 to 87% among the paired accessions. The level of diversity among different taxa/accessions observed during the present study was, however, low relative to the diversity level obtained due to RAPD markers in earlier studies. The pattern of genetic diversity neither matched with the known taxonomic classification, nor did it always match with the distribution of chemical constituents of the essential oils available in these accessions. Thus, present investigation though revealed poor correlation between the molecular and chemical diversity, indicating that chemical diversity in medicinal and aromatic species is not only result of genetic variability, but it also depends on a number of other factors. Thus this study may prove useful in several ways in Cymbopogon conservation and breeding programs and in the development of perfect markers though association mapping for genes involved in controlling agronomically important traits.

Keywords: Cymbopogon aromatic grasses; monoterpenoids; molecular markers; DNA polymorphism; genetic diversity and phylogenetic relationship; expressed sequence tag-simple sequence repeats (EST-SSRs).


(Pages 20-29) PDF Full text

Alterations in non-enzymatic antioxidant components of Catharanthus roseus exposed to paclobutrazol, gibberellic acid and Pseudomonas fluorescens

*Cheruth Abdul Jaleel, Ragupathi Gopi, Rajaram Panneerselvam

Abstract

The effect of different plat growth regulators like paclobutrazol (PBZ) gibberellic acid and Pseudomonas fluorescens treatments on the non-enzymatic antioxidant components of Catharanthus roseus was investigated in the present study. The treatments were given to plants by soil drenching on 38, 53, 68 and 83 days after planting (DAP). The plants were taken randomly on 45, 60, 75 and 90 DAP and separated into root, stem and leaves and used for determining antioxidant potentials. The non-enzymatic antioxidant contents like total phenol, ascorbic acid (AA), reduced glutathione (GSH) and ?-tocopherol (?-toc), were extracted and assayed from both control and treated plants. It was found that paclobutrazol (PBZ) gibberellic acid and Pseudomonas fluorescens treatments have a profound effect on the antioxidant metabolism and caused an enhancement in non-enzymatic antioxidant potentials under treatments in Catharanthus roseus. Our results have good significance, as this increase the innate antioxidant potential of this medicinal plant, as this plant being an essential component of traditional as well as modern pharmaceutical systems.

Keywords: Catharanthus roseus; paclobutrazol; antioxidants; Pseudomonas fluorescens; gibberellic acid

(Pages 30-40) PDF Full text



Approaches for enhancing salt tolerance in mulberry (Morus L) -A review

Kunjupillai Vijayan

Abstract

Mulberry (Morus) is a deciduous woody tree with moderate tolerance to salinity, which has great economic importance as its leaf is used for feeding the monophagous silkworm Bombyx mori L. Mulberry leaf is also used as fodder for livestock. The fruits of mulberry are highly nutritious and have many medicinal properties. In this review, effects of salinity on the morphological, physiological, biochemical and genetic characters in mulberry were discussed along with recent developments in salt stress research. Since mulberry is moderately resistant to salinity and a great degree of genotypic variation is found, it is possible to develop varieties with enhanced salt tolerance if appropriate strategies and techniques are adopted. An outline of such strategy was also drawn and discussed. Development of salt tolerant varieties can expand mulberry cultivation into the salt affected marginal lands, thereby increasing the availability of leaf for both sericulture and livestock industries in arid and semiarid regions of India and other Asian countries.

Keywords: Mulberry; sericulture; salinity; silkworm

(Pages 41-59) PDF Full Text