Mutagen Sensitivity Research Articles

Agro-morphological evaluation of gamma ray-induced mutant populations and isolation of harder grain mutants in wheat (Triticum aestivum L.)

Abstract Gamma ray-induced mutations have been widely used to improve existing crop germplasm and create novel genetic variation. In the current study, a multi-year experiment was carried out to induce and isolate mutants with desirable agro-morphological traits and improved grain hardness through evaluation of induced mutant populations generated in soft-textured wheat variety HPW 89 irradiated with gamma ray dose of 250, 300 and 350 Gy. Mutagen sensitivity studies revealed a higher frequency of biological damage and seedling mortality for doses beyond 300 Gy in the M1 generation. However, the mutagenic treatments in the M2–3 populations significantly altered the magnitude of the biometrical traits. Results from the variability and association studies among traits showed that biological yield per plant, 1000-grain weight, spike length, grains per spike and plant height may be prioritized for higher genetic gain and could be used as selection criteria parameters. Multivariate analysis indicated induction of heterogeneity among mutant populations. Overall, 250–300 Gy doses were found ideal for a successful wheat mutation programme and 293 agro-morphologically superior wheat mutants were identified, out of which 108 had semi-hard grain texture based on single kernel characterization system. Among these, nine mutants were found to have the highest grain hardness index due to induced changes in one or both puroindoline genes. Hence, these mutants identified for several traits along with harder grain texture will serve as important genetic resource in future wheat-breeding programmes.

Deciphering induced variability, character association and multivariate analysis utilizing gamma rays and ethyl methanesulfonate in bread wheat (Triticum aestivum L.) genotypes with differential grain texture

Purpose Sustainable wheat production and higher genetic gains can be realized by broadening the genetic base and improving the well adapted varieties. In the present study, a multi-year experiment involving induced mutagenesis was conducted to create genetic variation, assess trait associations and genetic divergence in four wheat varieties with differential grain texture treated with six doses of gamma rays and ethyl methane sulfonate using ten agro-morphological traits. Materials and methods Healthy selfed seeds of four bread wheat varieties with differential texture were irradiated using six doses ranging from 175 Gy-300 Gy of gamma rays (Co60: BARC, Mumbai) and six concentrations of ethyl methanesulfonate (0.3–1.3%) (Sigma-Aldrich, Bangalore, India) to evaluate variability, character association and degree of genetic diversity induced among the mutagenic treatments of wheat varieties with differential grain texture. Results Significant inter-population differences were observed for almost all the traits. The sample mean of twelve mutant populations in each of the cultivar exhibited superior quantitative phenotypic traits and increased values of the genetic parameters. Based on association and variability studies, plant height, spike length, grain filling period, biological yield per plant and harvest index can be used as early generation criteria for maximum genetic improvement. Multivariate studies indicated the contribution of various traits towards divergence and indicated the efficiency of mutagens in generating variability. Gamma-irradiation dosages between 200–250 Gy and 0.5–1.1% EMS for soft-textured varieties, whereas doses between 225–275 Gy and 0.5–0.9% EMS were found to be most potent for semi-hard-textured varieties. Conclusions Assessment of mutagen sensitivity showed that semi-hard wheat varieties were responsive to both mutagens, particularly EMS and generated higher variability and divergence than the soft textured varieties. Hence, gamma rays were proved to be more effective in generating higher variability than ethyl methanesulfonate. A total of 117 putative mutants were identified with desirable agro-morphological attributes. Among these, mutants with higher inter-cluster distance can be used as parents in hybridization programs and serve as important genetic resources in future wheat improvement programs.

Gamma Rays Sensitivity of Two Sesame cultivars in M1 Generation

The present study investigated the gamma ray sensitivity of two sesame (Sesamum indicum L.) varieties viz., AKT-64 and N-8 irradiated with five different doses from 400Gy to 700Gy. Germination percentage, root and shoot length, Survival percentage decreased gradually and observed a dose dependent relationship with an increase in dosage of gamma rays. N-8 showed a pronounced maximum reduction in germination percentage (28.44%) than AKT-64 (35.78%) at 700Gy, whereas survival percentage of AKT-64 (32.79%) and N-8 (26.45%) was drastically reduced at 700Gy dose. At a higher dose of 700Gy, root (2.42cm) and shoot (2.06cm) length of seedlings of N-8 were greatly inhibited. LD50 values that showed 50% reduction in biological parameters differed between AKT-64 and N-8. Based on all the biological parameters studied, the mutagen sensitivity of N-8 is higher than AKT-64. The overall considerations on M1 generation effects showed that N-8 were highly sensitive to gamma rays.

Mutagenic sensitivity analysis in soybean (Glycine Max L. Merill)

The seeds of soybean were treated with nine different doses of Gamma rays and six different doses of EMS to study the mutagenic sensitivity of physical and chemical mutagen. The treated seeds along with control were sown to raise M1 generation. Germination percentage was recorded in laboratory as well as in the field condition the higher doses showed drastic reduction in germination, and survival percentage. The Probit analysis showed that the LD50 value of Gamma rays based on laboratory and field germination was 335.68 Gy and 283.40 Gy respectively while for EMS it was 0.28% and 0.23% respectively.

Mutagenic sensitivity, effectiveness and efficiency of gamma rays and ethyl methane sulfonate on soft and semi-hard bread wheat (Triticum aestivum L.) varieties in the north-western Himalayan climate

Purpose The North-western Himalayan region requires unique varietal traits for the cultivation and quality of grain produced. Wheat varieties released for this zone in the past remained very popular among the farmers. However, with the passage of time certain traits such as the appearance of pathogenic rust races and grain softness have become threat to the fecundity of these genotypes and needs immediate improvement in this region. Mutation breeding facilitates improving one or two traits of a popular cultivar and to generate variability for most of plant traits upon which selection can be imposed. The purpose of this study is to evaluate the mutagenic sensitivity, effectiveness and efficiency of physical and chemical mutagens in four bread wheat varieties with differential grain texture. Materials and methods Four bread wheat varieties; HS 490, HPW 89, HPW 360 and HPW 251 were irradiated using six doses of gamma rays (γ-rays) ranging from 175 to 300 Gy; Co60 source (BARC, Mumbai, India) and six doses of ethyl methane sulfonate (EMS) ranging from 0.3 to 1.3%; EMS (Sigma-Aldrich, Bangalore, India) to assess their mutation sensitivity, effectiveness, efficiency and spectrum of induced macro-mutations in M1 and M2 generation. Results Based on mutagen sensitivity tests, both gamma rays and ethyl methane sulfonate had similar effects as the doses/concentrations increased in all four varieties. Ethyl methane sulfonate had a discernible effect on seed germination and growth parameters as compared to gamma irradiated treatments. Pollens viability studies confirmed the differential effects of both mutagens on germination and plant survivability. The LD50 and LC50 values varied between 290–315 Gy for gamma rays and 0.90–1.35% for EMS under controlled laboratory conditions, however, the range substantially differs for gamma rays (240–290 Gy) and for EMS (0.50–1.1%) under field conditions, irrespective of the variety treated. The frequency of chlorophyll mutations was low and showed a linear correlation with the doses/concentrations of the mutagen. A total of 117 putative mutants with desirable agro-morphological characteristics were also isolated. Mutagenic effectiveness and efficiency results showed that gamma irradiation doses of 250–300 Gy and ethyl methane sulfonate of 0.7–1.3% were most potent for an effective mutation breeding programme in wheat crop. Conclusions It was found that semi-hard textured varieties showed higher sensitivity to chemical mutagens as compared to soft-textured varieties. Gamma irradiation dose of 250–300 Gy and ethyl methane sulfonate concentration of 0.7–1.3% were found to be most effective and efficient across four bread wheat varieties and can be used in large scale mutagenesis programmes.

Cytomorphometric Analysis of Exfoliated Buccal Mucosal Cells and DNA Repair Proficiency in Peripheral Lymphocytes in Type 1 Diabetes Mellitus.

The aim of this study was to analyze the cytomorphometric changes in the buccal mucosal smears and to correlate the cytomorphometric findings and glycosylated hemoglobin (HbA1c) in type 1 diabetic (T1D) patients. In addition, DNA repair proficiency in peripheral lymphocytes of T1D patients was evaluated. Smears from the clinically normal buccal mucosa of 46 healthy subjects as controls and randomly selected 45 T1D patients, were stained using the Papanicolaou method, and the mean values (μm2) of nuclear area (NA), cytoplasmic area (CA), and cytoplasmic: nucleus ratio (CNR) were obtained for each patient. DNA damage in diabetics and control subjects was tested on peripheral blood samples using an in vitro mutagen sensitivity assay. Statistical analysis included Student's t-test, one-way ANOVA, and Pearson's correlation test to correlate cytomorphometric changes with HbA1c levels in both T1D and healthy control groups. The mean NA and CA values were higher in T1D while the mean CNR was found to be higher in the healthy control group. Statistical significance between the two groups was found only for the mean NA (P < 0.001) and mean CNR values (P < 0.001). A significant correlation was seen between HbA1c and CNR in both the T1D group (P = 0.015) and the healthy control group (P = 0.02). Significant differences were noted between the T1D and control subjects with regard to the frequency of damaged cells and DNA repair proficiency (P < 0.05). Significant cytomorphometric alterations were detected in the buccal mucosal cells of diabetic patients, which may aid in the early detection of diabetes or predict the risk for future disease complications among T1D patients.

Determination of mutagenic sensitivity and its manifestations on papaya (Carica papaya L.) cv. Arka Prabhath

Papaya is an important fruit crop of the family Caricaceae which needs the improvement in terms of virus resistance and shelf life with dwarf stature. Mutation breeding technique has been considered as an efficient tool adopted by plant breeders to create variability in papaya. The mutation frequency and population structure of the mutants directly depend upon the type of mutagen and the time of exposure. Irrespective of the used mutagens, the ultimate induced mutations are random and therefore determination of mutagenic sensitivity is important pre-requisite. Based on this, investigation on the induction of mutation in papaya cv. Arka Prabhath was carried out with the objective of creating genetic variability through physical mutagen. In this study, papaya seeds were irradiated with five different dose of gamma rays ranging from 50 Gy to 500 Gy. The results revealed that gradual reduction in germination, survival of seedlings and delayed germination with increase in dosage of gamma rays. Based on probit analysis, LD50 (Lethal dose) was fixed at 186.24 Gy. Total seven types of chlorophyll mutants were observed as a result of mutation. Mutagenic efficiency and effectiveness were higher in a lower dose of gamma treatment (50 Gy).

Evaluation of mutagenic susceptibility of different stages in germ cell development of Caenorhabditis elegans using whole genome sequencing.

In contrast to somatic mutations, mutations in germ cells affect every cell of any organism derived from the germ cell and therefore are related to numerous genetic diseases. However, there is no suitable assay to evaluate the mutagenic sensitivities of both male and female germ cells. The main type of Caenorhabditis elegans (C. elegans) is hermaphroditic, where spermatogenesis and oogenesis occur chronologically at specific stages, allowing induction of mutations in either sperm or eggs exclusively. In this study, we used the alkylating agent ethyl methanesulfonate and N-ethyl-N-nitrosourea to induce germline mutations in C. elegans at different developmental stages and analyzed mutation frequency and mutational spectrum from data gathered using next-generation sequencing (NGS) technology. Our results revealed low spontaneous mutation rates of C. elegans, along with distinct mutagenic effects elicited by the two mutagens. Our data show that the parental worms treated during germ cell mitosis, spermatogenesis, and oogenesis resulted in different mutation frequencies in their offspring, and female germ cells could be very susceptible to mutagen exposure during oogenesis. In summary, our study indicates that the use of C. elegans and its specific chronological hermaphroditism would be a promising way to explore the sensitivities of both male and female germ cells to mutagens.

Assessment of genotoxic instability markers in peripheral blood lymphocytes of breast cancer patients: a case control study

Changes in genetic constitution of an individual leads to uncontrollable cell growth and tumour formation. The acquisition of genomic instability predisposes cells to accumulate stable genome mutations causing carcinogenesis. The cytokinesis-block micronucleus cytome assay (CBMN), a well-established marker assay for chromosomal mutagen sensitivity, was applied in this study enrolling breast cancer patients and age and sex-matched controls. This work aimed to assess the predictive value of the frequency of genotoxic markers in peripheral blood lymphocytes for the risk/susceptibility of breast cancer. Samples from a hundred untreated breast cancer patients and age and sex matched controls were enrolled in the study from Government Medical College, Alappuzha. The genomic instability was assessed using cytokinesis block micronucleus assay where cytome events were marked. The results showed a significant increase in the frequency of micronucleus, nucleoplasmic bridge, and buds in the binucleated cells of breast cancer patients compared to the control samples. The variability was assessed by CBMN Cyt assay. The frequency of Micronuclei and Nucleoplasmic buds was significantly higher in the patient groups than in the controls (p < 0.0001). In Breast cancer patients, the median (IQR) range of MNi was 12(6), the Nucleoplasmic bridge 3(3) and the Nuclear buds were 2(1) and, in the controls, it was 6(5), 1(2) and 1(1) respectively. A larger difference in the frequency of genetic markers in cancer patients over control cases support a significant role of these markers in the population screening of individuals at high risk of cancer. Communicated by Ramaswamy H. Sarma

Assessment of Mutagenic Sensitivity and Lethal Dose of EMS in Papaya (Carica papaya L.) variety CO 7

Background: Mutagenesis is the process through which an organism’s genetic makeup is irreversibly altered. The objective of this study was to determine the optimal ethyl methanesulfonate (EMS) dosage to create desirable genetic variations in the papaya variety CO 7. Methods: The pre-soaked papaya seeds were exposed to five different concentrations of EMS (0.2%, 0.4%, 0.6%, 0.8% and 1.0%) for three hours. Non-treated seeds were used as a control. Data was recorded for germination per cent, seedling survival per cent, seedling length, girth, number of leaves, leaf length and width, petiole length and girth. Result: A declining trend in germination and growth of seedlings with the increase in EMS doses was observed. The probit curve analysis based on the seed germination percentage revealed that the LD50 value was found to be 0.55% EMS which was fixed as an optimal dose for large-scale mutagenesis experiments in papaya variety CO 7. The R2 value ranged from 0.73 to 0.99 and the growth reduction percentage (GR50) varied from 0.69 to 1.16 for different seedling traits studied. Since the optimization of mutagen dose would be expected to create desirable mutations with nominal biological damage, this study might assist further mutagenesis experiments in papaya.

Recommendations for laboratory testing of UK patients with acute myeloid leukaemia.

Recommendations for laboratory testing of UK patients with acute myeloid leukaemia.

Mutagen sensitivity and risk of second cancer in younger adults with head and neck squamous cell cancer: 15-year results

PurposeTo evaluate the mutagen sensitivity phenotype on the risk of second primary cancer (SPC) in patients with head and neck squamous cell carcinoma (HNSCC), and to estimate the long-term rate of SPC and the outcome with SPC.MethodsA survey was made regarding SPC among 124 younger (≤ 50 years) adults with HNSCC who were enrolled in a pretreatment mutagen sensitivity investigation during 1996–2006. Mutagen sensitivity was assessed by exposing lymphocytes to bleomycin in vitro and quantifying the bleomycin-induced chromatid breaks per cell (b/c). Patients were classified as hypersensitive (> 1 b/c) or not hypersensitive (≤ 1 b/c).ResultsMean follow-up time for all patients was 68 months (range: 5–288 months), and the 15-year cancer-specific survival was 15%. Twenty patients (16%) developed a SPC (15-year estimated rate: 41%), and half of them was hypersensitive. The crude rate of SPC for hypersensitive (n = 65) or not hypersensitive (n = 59) patients were 15 and 17%, respectively (p = 0.4272). The 15-year estimated rate of SPC for hypersensitive and not hypersensitive patients was 36 and 48%, respectively (p = 0.3743). Gender, UICC stages, anatomical sites of index cancer did not prove to be a significant risk factor for SPC. Forty-five percent of SPC developed after the 10-year follow-up. The 3‑year cancer-specific survival was 23% with SPC.ConclusionAccording to our findings, mutagen hypersensitivity was not associated with an increased SPC risk in HNSCC patients. Patients are at a lifelong risk of developing a SPC. Survival with SPC is very poor.

A three-gene cluster in Trichoderma reesei reveals a potential role of dmm2 in DNA repair and cellulase production

BackgroundThe ascomycete Trichoderma reesei is one of the most efficient industrial producers of cellulase. Gene targeting by homologous recombination is a key technique for improving strains and constructing mutants. In T. reesei, tku70 (homologous to human KU70) was deleted to block non-homologous end-joining, which led to 95% of transformants exhibiting homologous recombination.ResultsTwo genes located in close proximity to tku70 were identified: the ferrochelatase gene hem8 (tre78582, homologous to Aspergillus niger hemH and Cryptococcus neoformans HEM15) and a putative DNA methylation modulator-2 gene dmm2 (tre108087, homologous to Neurospora crassa dmm-2). Genome-wide surveys of 324 sequenced fungal genomes revealed that the homologues of the three genes of interest are encoded in tandem in most Sordariomycetes. The expression of this three-gene cluster is regulated by blue light. The roles of these three genes were analyzed via deletion and complementation tests. The gene hem8 was originally described as a novel and highly distinct auxotrophic marker in T. reesei and we found that the product protein, HEM8, catalyzes the final step in heme biosynthesis from highly photoreactive porphyrins. The lethal phenotype of the hem8 deletion could be overcome by hematin supplementation. We also studied the functions of tku70 and dmm2 in DNA repair using mutagen sensitivity experiments. We found that the Δtku70 strain showed increased sensitivity to bleomycin, which induces DNA double-strand breaks, and that the Δdmm2 strain was sensitive to bleomycin, camptothecin (an inhibitor of type I topoisomerases), and hydroxyurea (a deoxynucleotide synthesis inhibitor). The double-mutant Δtku70&dmm2 showed higher sensitivity to hydroxyurea, camptothecin, and bleomycin than either of the single mutants. Knockout of dmm2 significantly increased cellulase production.ConclusionsOur data show, for the first time, that ferrochelatase encoded by hem8 catalyzes the final step in heme biosynthesis from highly photoreactive porphyrins and that dmm2 encodes a putative DNA methylation modulator-2 protein related to DNA repair and cellulase expression in T. reesei. Our data provide important insights into the roles of this three-gene cluster in T. reesei and other Sordariomycetes and show that the DNA methylation modulator DMM2 affects cellulase gene expression in T. reesei.

ASSESSMENT OF SEED GERMINATION IN BLACKGRAM (VIGNA MUNGO L. HEPPER) UNDER EMS INDUCED MUTAGENESIS

The present investigation was carried out to estimate the mutagenic sensitivity of blackgram accession IC 436524 with EMS (Ethyl methane sulfonate). The seeds of IC436524 were treated with four different concentrations of EMS viz., 0.2%, 0.3%, 0.4% and 0.5%. Thirty seeds of each concentration were placed in Petri plates in three replication along with untreated seeds for germination test, shoot length(cm) and root length(cm). The germination was observed on the 5th day after treatment while shoot and root length of seedling was recorded on the 10 day. The results showed that the germination% was recorded highest (86.67%) at 0.2% of EMS followed by (80.00%) at 0.3% of EMS and lowest seed germination% was recorded at 0.4 and 0.5% of EMS. The reduction percentage of seed germination with control (untreated seeds) at 0.2% of EMS was 6.66% followed by 13.33% at 0.3% of EMS, 53.33% at 0.4% of EMS and 80% at 0.5% of EMS respectively. The results also showed that the highest shoot and root length (cm) was recorded at 0.2% of EMS (8.60cm and 5.50cm) followed by at 0.3% of EMS (6.50cm and 3.83cm). Thus 0.4 and 0.5% dose of EMS seemed very effective in reducing percent seed germination in black gram. The results excerted that the blackgram accession IC436524 could be germinated up to 0.3% EMS concentration to create variability in blackgram which are further useful for crop improvement programs.

Induced Mutants in Locally Adapted Landraces of French Bean (Phaseolus vulgaris L.), their Mutagenic Sensitivity and Mutability for Crop Improvement

Induced Mutants in Locally Adapted Landraces of French Bean (Phaseolus vulgaris L.), their Mutagenic Sensitivity and Mutability for Crop Improvement

Induced variability and assessment of mutagenic effectiveness and efficiency in sorghum genotypes [Sorghum bicolor (L.) Moench

Purpose Sorghum is an important cereal crop, cultivated for food, fodder and biofuel. Mutation breeding techniques are used to create genetic variability for qualitative and quantitative traits in crop plants. The purpose of this study was to create induced variability and estimate mutagenic effectiveness and efficiency of physical and chemical mutagens in two sorghum cultivars. Materials and methods Gamma rays (100, 200, 300 and 400 Gy, Co60 source, Bhabha Atomic Research Center, Mumbai, India), ethyl methane sulfonate (0.1%, 0.2%, 0.3%, and 0.4% EMS, Sigma-Aldrich, Bangalore, India) and their combinations were used to mutagenize 296B (rainy season) and Parbhani moti (post-rainy) cultivars. Morphological and yield traits were analyzed for enhanced variability in qualitative and quantitative traits across M2 and M3 generations. Results Based on the mutagenic sensitivity, lethal dose at 50% survivability (LD50) for both the genotypes was found to be 269–281 Gy in case of gamma rays and 0.32–0.33% for EMS. Based on reduced germination and survivability, mutagenic sensitivity was dose dependent and genotype independent. High frequency of chlorophyll mutations (albino, xantha, viridis, variegated and chlorina) was linearly correlated with dose in both the genotypes. Among the favorable mutants, dwarf and brown midrib were isolated from Parbhani moti population, which could be used in the cross breeding programs. A combined treatment, 100 Gy + 0.1% EMS showed high mutagenic effectiveness and efficiency. Enhanced genetic variation for quantitative traits as measured by wide range values and coefficient of variation was attributed to the effect of physical and chemical mutagens. Early flowering and high grain yield (24–49% increase over control) mutants were identified in M2 and validated in M3 generation in both genotypes. Conclusions This study has revealed wide genetic variability and better effectiveness and efficiency of the physical (300 Gy) and chemical mutagens (0.2%) and their combination (200 Gy + 0.2%) across two sorghum genotypes. Significant correlations identified between quantitative traits will help in better selection in the segregating generations.

Assessment of mutagenic sensitivity in blackgram variety CO 6

The present study was conducted to examine the mutagenic effect of 60Co gamma rays and a combination of 60Co gamma rays with EMS in blackgram variety CO 6. Based on the LD50 dose, the seeds were treated with three different doses of gamma rays (200, 300, 400 Gy) and recurrent doses of 20 mM and 30 mM EMS were treated with gamma ray irradiated seeds for combination treatments. The M1 generation was evaluated in the field for the following parameters viz., germination percentage, plant survival percentage, plant height at 30 DAS and maturity, pollen fertility and seed fertility. A dose-dependent decrease was noticed for all the characters under this study in M1 generation. Overall, the maximum reduction was noticed at a higher dose of 400 Gy gamma rays and 400 Gy + 30 mM EMS mutagenic treatments. Among the mutagenic treatments, a combination of 60Co gamma ray + EMS exhibited the maximum effect with a higher percentage of reduction in all the traits while increased pollen sterility was found to be associated with a corresponding increase in dose/concentration of mutagenic agents. A significant positive correlation was observed between viable mutation frequency and biological damage caused by mutagens in M1 generation. Hence, the higher doses of 60Co gamma rays (300 and 400 Gy) and 60Co gamma rays +EMS (300 Gy+ 30; 400 Gy+ 20 and 400 Gy+ 30 mM) proved to be efficient in increasing the mutation frequency towards desirable directions. Key wordsBlackgram, combination treatment (60Co gamma rays + EMS), 60Co gamma rays, mutation breeding.

Determination of gamma rays induced mutagenic sensitivity of guava (Psidium guajava L.) cv. ‘Lalit' and ‘Shweta’

In the present investigation, seeds of guava cv. ‘Lalit' and ‘Shweta' were irradiated with different dosages of gamma rays ranging from 25 to 150 Gy using the 60Co source to examine its effects on morphological and physiological traits. The LD50 value calculated on the basis of germination percentage of irradiated seedlings using probit curve analysis, was 57.81 Gy and 57.42 Gy for ‘Lalit' and ‘Shweta', respectively. Seed germination and growth parameters viz., plant height, internode number, internodal length and leaf dimensions had negative correlation with gamma irradiation., while the parameters, number of leaves and branches experienced the hormetics radiostimulant effect at lower dosage (up to 50 Gy), but a marginal reduction was observed at higher dosages (125–150 Gy). Reduction in stomatal number with increased stomatal size were observed in the mutant populations. With ascending irradiation doses, a marginal signifcant reduction was observed in leaf chlorophyll content. The results of this study will allow implementation of mutagenesis-based genetic improvement programmes in guava and, serve as a morphological and physiological marker to identify some desirable mutants at early stage.

Radiation sensitivity of sesame (Sesamum indicum L.) genotypes in M1 generation

The present study investigated the gamma ray sensitivity of two sesame (Sesamum indicum L.) varieties viz., SVPR1 and TMV7 irradiated with five different doses from 250 Gy to 450 Gy at 50 Gy intervals. Germination percentage, root and shoot length, pollen fertility (%) decreased gradually and observed a dose dependent relationship with an increase in dosage of gamma rays. Survival percentage recorded irregular decreasing trend with upsurge in survival rate at certain doses. SVPR1 showed a pronounced maximum reduction in germination percentage (37.5%) than TMV7 (40.05) at 450 Gy, whereas survival percentage of TMV7 (20.02%) and SVPR1 (19.5%) was drastically reduced at 250 Gy itself. At a higher dose of 450 Gy, root (3.08) and shoot (3.03) length of seedlings of SVPR1 were greatly inhibited. Pollen fertility percentage showed a linear reduction irrespective of the genotypes, and maximum reduction was rear at 450 Gy in SVPR1 (62.76%) was recorded. LD50 values that showed 50% reduction in biological parameters differed between TMV7 and SVPR1. Based on all the biological parameters studied, the mutagen sensitivity of SVPR1 is higher than TMV7. The overall considerations on M1 generation effects showed that SVPR1 were highly sensitive to gamma rays.

The msh1 gene is responsible for short life span mutant natural death and functions to maintain mitochondrial DNA integrity

Wild-type filamentous fungus Neurospora crassa continues to grow its hyphae for a very lengthy period of time (>2 years), whereas mutations at the natural death (nd) locus shorten life span (approximately 20 days). By positional cloning based on heat augmented mutagen sensitivity of the nd strain, we identified a nonsense mutation in the msh1 gene, an eukaryotic homolog of bacterial MutS, and this mutation resulted in encoding non-functional polypeptide. By tagging with GFP, subcellular localization of the MSH1 protein in the mitochondria was observed, and knock out of the msh1 gene caused severe growth deficiency accompanying mitochondrial DNA (mtDNA) aberrations such as large-scale mtDNA deletions and rearrangements as seen in the nd strain. These results suggested that MSH1 may maintain mtDNA integrity. Thus, loss of function compromises mtDNA, leading to the acceleration of cellular aging.