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[en] Based on 2,500 herbarium vouchers of the subgenus Seriphidium of Artemisia, which were collected from 21 sites across Central and NW-Balochistan, morphological studies and detailed drawings of stem leaves were performed with the aim to be able to identify the most common Artemisia species of Balochistan by a few vegetative characters. The following species were recognized: Artemisia quettensis (most common and endemic species in the area), A. turanica, A. oliveriana, A. sieberi, A. stenocephala, and A. santolina. Some presumed hybrid species had intermediate morphological characters, such as A. quettensis x A. oliveriana, A. quettensis x A. turanica, A. oliveriana x A. turanica, and A. oliveriana x A. sieberi. Key characters of the species, illustrations, and data on the distribution were provided. The frequent polyploidization and hybridization processes within this species complex were emphasized, and the effects on speciation and habitat preference were discussed. The present study also suggests a possible relationship between species distribution patterns, xeromorphism and climatic factors, varying from northeast to southwest Balochistan. (author)
[en] The paper describes the potential use of in vitro culture systems of Dactylis glomerata L. for inducing and recovering mutants, avoiding or dissolving chimeras and mass propagation of mutant phenotypes. Specifically, the systems rely on the production of embryos directly from mesophyll cells of plated leaf segments and the full development of embryos directly in liquid suspension cultures. Since embryos appear to arise from single cells, the leaf-culture system could be used both to avoid chimerism in mutation induction and selection experiments and to dissolve existing chimeras. Since D. glomerata is an autotetraploid, chances for the recovery of completely homozygous recessive (nulliplex, aaaa) mutants would be greatly improved if plants could be scaled down to the 2x chromosome number using haploidy techniques, of if 2x plants could be regenerated from gametic cells. Mutagenic treatment of either 2x gametes or 2x plants could even allow for the recovery of nulliplex plants from a triplex (AAAa) genotype. The avoidance of chimerism in mutagenic treatment of cell-suspension cultures is not as clear-cut. Even though embryos probably have a single cell origin, it is not possible to state unequivocally that any aggregation of two or more cells is not of the same lineage and will not contribute to the same embryo. The system may, however, be used to dissolve chimeras. The full development of embryos directly in liquid medium and their ability to germinate directly into plants offer a unique potential for mass vegetative propagation of mutants or other selected genotypes. Further refinements of the system are needed to synchronize embryo development, establish embryos or seedlings into workable propagation modes and to incorporate the embryogenic trait into a wider range of genotypes. (author)
[en] A study was undertaken to find out the estimates of genetic variability, genetic parameters and character association among different flower traits between three gladiolus cultivars viz: Sancerre, Fado and Advanced Red. The experiment was repeated three times by using RCBD (Randomized complete block design) at Department of Horticulture, PMAS-UAAR, Rawalpindi. The highest genotypic coefficient variation (GCV) and phenotypic coefficient variation (PCV) magnitude was observed for spike length (16.00) and number of florets per spike (14.84) followed by number of leaves (10.00). Among the traits studied the highest heritability estimates was recorded in spike length (99.5 percent) followed by number of florets/spike (99.6 percent) and lowest in plant height (98.2 percent). The genetic advance as percent of mean was ranged from 2.8 percent to 24.75 percent. Genetic advance was highest for floret breadth (24.75 percent) and lowest for plant height (2.8 percent). High heritability combined with high genetic advance was noticed for number of florets per spike, spike length and floret breadth indicating additive gene action which suggested that improvement of these traits would be effective for further selection of superior genotypes. Plant height and number of florets per spike showed highly positive and significant association with spike length, number of leaves, leaf area, floret length and floret breadth while, spike length registered positive and significant correlation with number of leaves and floret breadth. The path coefficient analysis based on spike length, as responsible variable exposed that all of the traits exerted direct positive effect except leaf area and floret length. Spike length imparted maximum positive direct effect on the number of florets per spike. Hence, spike length and number of florets per spike may be considered for further improvement. However, Floret length and floret breadth may also be considered as a criterion for selection. (author)
[en] The discussion in the paper centres on the in vitro selection of mutants relevant to agriculture. First, the advantages of in vitro selection are assessed. Second, the major targets for selection are listed: efficiency of nutrient uptake/utilization and of carbon fixation; nutrient quality of the crop; and resistance to temperature stress, water stress, flooding, heavy metals, pollutants, herbicides, pathogens and pests. Third, the two major in vitro selection strategies are described and evaluated: (1) the imposition of stress and (2) recognition of biochemical markers. Attention is drawn to recent developments in in vitro selection for characters to be used in molecular cell genetics, especially the selection of auxotrophs and antibiotic-resistant lines and the use of negative selection procedures. It is concluded that good progress is being made in the in vitro selection of agriculturally relevant target characters, but some problems remain. Fourth, the suitability of the following types of culture for in vitro selection is discussed and evaluated: (1) haploid cultures; (2) pollen/microspores, cell suspensions, protoplasts, callus, embryos/embryoids and regenerating plantlets. Finally, in vitro selection for one agriculturally relevant character, resistance to pathogens, is analysed in detail. Four selection strategies are considered: (i) challenge with pathogen propagules; (ii) exposure to pathotoxins; (iii) exposure to toxic culture filtrates; (iv) selection based on identification of biochemical or molecular markers known to be coorelated with resistance. It is concluded that steady progress has been made so far in the development of the first three strategies. Development of the final strategy will require more research, but rapid advances are expected in the near future. (author)
[en] In this study, karyotype criteria of 27 accessions (17 taxa) of the two tribes Asclepiadeae (20 accessions) and Ceropegieae (7 accessions) from Egypt and Saudi Arabia belonging to subfamily Asclepiadoideae are described and polyploid variations are also discussed. Detailed karyotype features, i.e. total chromosome length (TCL), mean chromosome length (MCL) and karyotype asymmetry expressed as arm ratio (MAR), total form percent (TF %), intrachromosomal asymmetry (A1) and interchromosomal asymmetry (A2), are also described. Karyotype features of the studied accessions were used to assess the tribal relationships within the subfamily Asclepiadoideae to differentiate between taxa that belonging to the tribes Asclepiadeae and Ceropegieae in the light of the current systems of classification. In addition, new chromosome counts of 16 taxa or accessions are reported here for the first time. (author)
[en] Haploid are plants with a gametophytic chromosome number and doubled haploid are dihaploids that have undergone chromosome duplication. The production of haploid and doubled haploid (DHs) through gametic embryogenesis allows a single-step development of complete homozygous lines from heterozygous parents, shortening the time required to produce homozygous plants in comparison with the conventional breeding methods that employ several generations of selfing. The production of haploid and DHs provides a particularly attractive biotechnological tool, and the development of haploidy technology and protocols to produce homozygous plants has had a significant impact on agricultural systems. Nowadays, these bio technologies represent an integral part of the breeding programmes of many agronomically important crops. There are several available methods to obtain haploid and DHs, of which in vitro anther or isolated microspore culture are the most effective and widely used (Germana Maria 2011). Tissue culture techniques, particularly short-term culture procedures such as shoot-tip culture and regeneration from primary explants, have been proposed as methods for obtaining large numbers of plants identical to the plant used as an explant source( Evans et al., 1984). Nicotiana spp. are one of the most important commercial crops in the world ( Liu and Zhang, 2008). Nicotiana alata is member from family solanacea, it is ornamental plant and the diploid cells contains 18 chromosomes. Nitsch (1969) reported the first production of haploid plants through anther culture and regeneration of plants of Nicotiana alata, For these reasons they have been considered to suitable candidates for model species in somatic cell genetics research( Bourgin et al., 1979). Radiobiological studies on plant tissues in culture may provide information on the cell growth behavior, radiosensitivity and the induction of mutations. The radiosensitivity of plants and calli can be manifested mostly in three ways: 1) inhibition of growth, 2) reduction of reproduction capacity and 3) death. growth inhibition induced by ionizing radiation has been attributed to chromosome deletion (Sparrow et al. 1961) and changes in a variety of biochemical and physiological systems Gunckel and Sparrow, (1961). Irradiation with gamma rays may provide and insight into the mechanism of action of radiation in producing physiological and genetic variability, thus it has been directly used to produce useful variation in quantitatively inherited characters, such as quality and maturity time (Brock, 1970). Salinity is a major factor limiting the crop productivity in the semi arid area of the world (Robinson, 1986). Salinity inhibits plant growth by one or more of the three principle ways; 1st. ion toxicity (mainly of Na+ and Cl-), 2nd. osmotic stress and the 3rd. nutritional disruption (Yeo et al., 1991). These include genetic variability between species, or among cultivars within species and duration and timing of exposure to salinity (Cushman et al. 1990) they added that salt tolerance of halophytes depends on the constitutive expression of several genes in response to salt stress. The application of mutagens in tissue culture in vitro to enhance the rates of spontaneous mutations and the use of direct selection for the screening of spontaneous mutants or variant lines, have been used in several laboratories. In addition, an increase in genetic variability may be induced in large and homogeneous populations of plant cells or in callus tissues, by exposing cultures to physical or chemical mutagenic agents. These are capable of increasing the frequency of changes in the genetic material when the cultures are under conditions which allow for the rapid screening of the mutants. These conditions may also be used to select and recover spontaneous variants or mutants directly from untreated material. The main types of mutants are (1) auxotrophic, which require nutritional supplements for normal growth, (2) resistant, which resist specific drugs, antimetabolites, or abnormal environmental or nutritional condition and (3) autotrophic mutants, that grow in deficient media and are capable of synthesizing some substances normally required for wild lines. The use of mutagenesis and in vitro induce mutation should provide a new input to the solution if breeding problems in crop plant (Ancora and Sonnino, 1987). The aim of the present investigation is production of haploid plants through anther culture in N. alata and study the effect of gamma rays, salt stress and combined effect between them on it. Morever, determining the changes in the internal composition of the cell as proline and protein. Also, to study the molecure diversity as revealed by; Protein Acrylamid Gel Electrophoresis - SDS (PAGE-SDS), Random Amplified Polymorphic DNA (RAPD) .
[en] Directed and undirected mutagenesis continues to offer unique opportunities for crop improvement. Mutations also occur naturally and different forms are present in each strain of plants within and among species. Modifying genes affect the expression of all mutants and examples exist where the deleterious features of a mutant can be significantly changed by selection. New technologies, including those associated with genomics such as re-sequencing, TILLING, and RNA interference, allow the detection of gene variation at an unprecedented frequency. Knowledge of genes that affect recombination among homoeologous chromosomes may lead to inducible methods regulating the exchange among chromosomes in a polyploid species. Forward and reverse genetic methods are readily available in many species, including model plant species. There are an estimated one million sites in the japonica rice genome tagged via Tos17, Ac/Ds, T-DNA, and other insertion elements. Site-specific mutagenesis and gene replacement methods may replace the need for transgenic technology in some cases. Transcriptome modification occurs via mutagen treatment, aneuploidy, and uniparental chromosome loss, and sometimes results in a mutant phenotype. The boundaries of gene variation appear to be more expansive as plant genetics knowledge and technologies increase. (author)
[en] Anogenital cancers and head and neck cancers are causally associated with infection by high-risk human papillomavirus (HPV). The mechanism by which high-risk HPVs contribute to oncogenesis is poorly understood. HPV16 encodes three genes (HPV16 E5, E6, and E7) that can transform cells when expressed independently. HPV16 E6 and E7 have well-described roles causing genomic instability and unregulated cell cycle progression. The role of HPV16 E5 in cell transformation remains to be elucidated. Expression of HPV16 E5 results in enlarged, polyploid nuclei that are dependent on the level and duration of HPV16 E5 expression. Live cell imaging data indicate that these changes do not arise from cell-cell fusion or failed cytokinesis. The increase in nuclear size is a continual process that requires DNA synthesis. We conclude that HPV16 E5 produces polyploid cells by endoreplication. These findings provide insight into how HPV16 E5 can contribute to cell transformation.
[en] The p53 tumour suppressor protein has defined roles in G1/S and G2/M cell cycle checkpoint in response to a range of cellular stresses including DNA damage, dominant oncogene expression, hypoxia, metabolic changes and viral infection. In addition to these responses, p53 can also be activated when damage occurs to the mitotic spindle. Initially, spindle damage activates a p53-independent checkpoint which functions at the metaphase-anaphase transition and prevents cells from progressing through mitosis until the completion of spindle formation. Cells eventually escape from this block (a process termed 'mitotic slippage'), and an aberrant mitosis ensues in which sister chromatids fail to segregate properly. After a delay period, p53 responds to this mitotic failure by instituting a G1-like growth arrest, with an intact nucleus containing 4N DNA, but without the cells undergoing division. Cells lacking wild-type p53 are still able to arrest transiently at mitosis, and also fail to undergo division, underscoring that the delay in mitosis is p53-independent. However, these cells are not prevented from re-entering the cell cycle and can reduplicate their DNA unchecked, leading to polyploidy. Additionally, p53-null cells which experience spindle failure often show the appearance of micronuclei arising from poorly segregated chromosomes which have de-condensed and been enclosed in a nuclear envelope. The ability of p53 to prevent their formation suggests an additional G2 involvement which prevents nuclear breakdown prior to mitosis. The molecular mechanism by which p53 is able to sense mitotic failure is still unknown, but may be linked to the ability of p53 to regulate duplication of the centrosome, the organelle which nucleates spindle formation. (authors)