Girjesh Kumar

Genetic loss through heavy metal induced chromosomal stickiness in Grass pea.

Abstract Cytogenetic studies were carried out to evaluate the genotoxic effect of two heavy metals viz. lead (Pb) and zinc (Zn) on the gametic cells of grasspea (Lathyrus sativus). Our study presented a severe case of chromosome stickiness in meiosis impairing normal chromosome segregation. This phenomenon persisted upto microspore stage. The manifestation of stickiness ranged from mild to intense followed by chromosome degeneration. Stickiness taken together with abnormal spindles, irregular chromosome segregation, pycnotic nuclei were considered the most probable causes of low pollen fertility found in both metal treatments at higher doses.

EMS-induced cytomictic variability in safflower (Carthamus tinctorius L.).

Seeds of safflower (Carthamus tinctorius L.) were subjected to three treatment durations (3, 5 and 7 h) of 0.5% Ethyl Methane Sulphonate (EMS). Microsporogenesis was carried out in the control as well as in the treated materials. EMS treated plants showed interesting feature of partial inter-meiocyte chromatin migration through channel formation, beak formation or direct cell fusion. Another interesting feature noticed during the study was the fusion among tetrads due to wall dissolution. The phenomenon of cytomixis was recorded at nearly all the stages of microsporogenesis connecting from a few to several meiocytes. Other abnormalities such as laggards, precocious movement, bridge and non-disjunction of chromosomes were also recorded but in very low frequencies. The phenomenon of cytomixis increased along with the increase in treatment duration of EMS. Cells with these types of cytomictic disturbances may probably result in uneven formation of gametes or zygote, heterogenous sized pollen grains or even loss of fertility in future.

Characteristics of cytomixis in the pollen mother cells of green manure crop Sesbania cannabina

Cytomixis has been reported in many plant species, but there is no published report in Sesbania cannabina spp. The cytological stability of any plant is an important consideration in view of its extensive use in genetics and plant breeding programmes. Present study reveals the occurrence of inter PMC (pollen mother cell) transfer of chromatin material. During present investigation, it was found that out of different doses of gamma rays + ethylmethane sulfonate, the highest dose displayed the highest instances of cytomixis. In present investigation, the phenomenon of cytomixis can be observed between 2 to 10 PMCs. During male meiosis, it occurs through narrow and broad cytoplasmic channels or through direct contact between PMCs from early prophase to late telophase stage. However, the frequency of its occurrence during late meiotic stages is rather low. It elucidates that in Sesbania cannabina, induced cytomixis results into possible sources for production of aneuploids and polyploids. This may be further useful in plant breeding programmes to improve genotypic and phenotypic characters of Sesbania cannabina.

Induced cytomictic diversity in maize (Zea mays L.) inbred

Mutation breeding has been used for improving oligogenic and polygenic characters, disease resistance and quantitative characters including yielding ability. The cytological stability of maize inbred lines is an important consideration in view of their extensive use in genetics and plant breeding research. Investigation in Zea mays L. confirms that the migration of chromosomes is a real event that cannot be misunderstood as an artifact produced by fixation or mechanical injuries. During present investigation, we found that out of six inbred lines of Zea mays L. viz. CM-135, CM-136, CM-137, CM-138, CM-142 and CM-213 at various treatment doses of gamma irradiations viz. 200, 400 and 600 Gy, some of the plants of inbred line CM-138 at 200 Gy dose displayed characteristic cytoplasmic connections during all the stages of meiosis. Four plants from this treatment set were found to be engaged in a rare phenomenon reported as “Cytomixis”. It elucidates that in inbred of Zea mays L., induced cytomixis through gamma rays treatment may be considered to be a possible source of production of aneuploid and polyploid gametes. This phenomenon may have several applications in Zea mays L. improvement in the sense of diversity and ever yield potential.

Genetic Damage Induced by a Food Coloring Dye (Sunset Yellow) on Meristematic Cells of Brassica campestris L.

We have performed the present piece of work to evaluate the effect of synthetic food coloring azo dye (sunset yellow) on actively dividing root tip cells of Brassica campestris L. Three doses of azo dye were administered for the treatment of actively dividing root tip cells, namely, 1%, 3%, and 5%, for 6-hour duration along with control. Mitotic analysis clearly revealed the azo dye induced endpoint deviation like reduction in the frequency of normal divisions in a dose dependent manner. Mitotic divisions in the control sets were found to be perfectly normal while dose based reduction in MI was registered in the treated sets. Azo dye has induced several chromosomal aberrations (genotoxic effect) at various stages of cell cycle such as stickiness of chromosomes, micronuclei formation, precocious migration of chromosome, unorientation, forward movement of chromosome, laggards, and chromatin bridge. Among all, stickiness of chromosomes was present in the highest frequency followed by partial genome elimination as micronuclei. The present study suggests that extensive use of synthetic dye should be forbidden due to genotoxic and cytotoxic impacts on living cells. Thus, there is an urgent need to assess potential hazardous effects of these dyes on other test systems like human and nonhuman biota for better scrutiny.

Effect of waterlogging stress on meiotic course, tetrad formation and pollen fertility of Sesbania pea

Sesbania cannabina a multipurpose leguminous crop of family Fabaceae, is widely adaptable to adverse climatic conditions such as waterlogging, drought and high salinity. Flooding and water logging are very common phenomena and there may be possibility to become more serious alarms for environment, which is progressively deteriorated by human beings by their anthropogenic activities, polluting the atmosphere. Flooding provides a case of natural selection to the nature which selects the plants which are more adaptable to this condition and renders themselves to survive due to this tolerance or resistance behavior. Present study envisages the effect of waterlogging stress on chromosomal biology of Sesbania pea. To study the effect of waterlogging stress on microsporogensis of Sesbania cannabina, presoaked seeds were sown in experimental pots. Permanent waterlogged condition is created by shifting pots in water filled tanks. Cytological studies showed various types of chromosomal aberrations induced by waterlogging stress and reduction in pollen fertility was also encountered.

Sodium Azide Induced Complementary Effect of Chromosomal Stickiness in Brassica Campestris L.

Present investigation reports the mutagenic efficacy of sodium azide with a view to study its effects on meiotic behavior and phenotypic quantitative traits of Brassica campestris L. Seeds were treated with three concentration of sodium azide i.e. 0.3%, 0.5% and 0.7%, along with control. Morphological/phenotypic parameters studied were plant height, number of primary branches, number of secondary branches, seeds/siliqua, husk yield, seed yield and 1000-seed weight. All these traits showed the significant positive shifts in mean at 0.3% and 0.7% doses of azide as compared to control and 0.5% dose. However, cytogenetic assessment of the treated plants clearly revealed the preponderance of stickiness distributed in all the phases of meiotic division that persisted up to the tetrad stage. The phenomenon displayed mild to severe case of stickiness on the basis of number of genome involved during meiosis. Manifestation of stickiness has also been resulted in several other meiotic abnormalities such as bridge (1.88%), unorientation (0.64%), micronuclei (1.38%), asynchronous division (0.77%), and precocious chromosomes (3.89%) along with some other anomalies (laggards, univalents etc.). Frequency of these anomalies along with severe stickiness was higher at 0.5% dose of azide that must have compromised with pollen fertility resulting declined fertility rate. Though, pollen fertility at 0.3% and 0.7% doses had not been much affected and had fallen near control. Thus, from present investigation inference can be drawn that the sodium azide induced stickiness might have resulted in some meiotic mutant that has imposed some novel genetic combinations thereby positively affecting morphological traits of the crop.

Consequences of colchicine induced intermeiocyte connections in Helianthus annuus

During microsporogenesis sometimes the chromatin materials migrate from one cell to another by intermeiocyte connections. In the present study, during induction of tetraploidy in sunflower, changes in the normal behaviour of chromosomes was detected. Besides chromosomal aberrations, cytomictic connections were frequently recorded. Cytomixis has been reported by many researchers in many diploid or tetraploid plants. In sunflower, cytomixis in colchiploids has not been recorded. In the current study high numbers of cytoplasmic connections were observed in the plants failing to reach higher ploidy level. Formation of cytoplasmic connections was very high, leading to many hyperploids, hypoploids and even empty pollen mother cells (PMCs). Cytomixis occurred frequently, with two to many meiocytes engaged in exchange of chromatin through one or multiple cytoplasmic connections. Few rare polyploid PMCs with cytoplasmic connections were observed, which favours formation of aneuploids and polyploids. Besides various chromosomal anomalies, fertility was also significantly affected. This work envisages the possibility that although polyploidy was not achieved in some plants there is tendency to form higher ploidy levels in this species. This illustrates the potential for formation of various genetic combinations and thus novel traits. Cytomixis is also an additional source of male sterility in sunflower and thus requires intense research.

Induction of cytomixis affects microsporogenesis in Sesamum indicum L. (Pedaliaceae)

Cytomixis was recorded during microsporogenesis in sesame (Sesamum indicum L.), a member of the family Pedaliaceae. The phenomenon of cytomixis was observed at various stages of meiosis in 0.5% sodium azide (SA) treated populations of Sesamum indicum L. Cytomixis was observed to occur through various methods, i.e. by forming cytoplasmic channels and direct fusion of pollen mother cells (PMCs), the former was more frequent than the latter. The migration of nuclear content involved all the chromatin/chromosomes or part of it from donor to recipient cell/cells. Some completely empty meiocytes were also observed. Stickiness, precocious movement, laggards, unorientation and micronuclei were observed in almost all the sets treated with various doses of SA. Increase in the doses of SA had a positive effect on the percentage of PMCs showing cytomixis and chromosomal abnormalities. The impact of cytomixis on meiotic behaviour, reduced pollen viability and heterogeneous sized pollen grains were observed.

Comparative Genotoxicity of Herbicide Ingredients Glyphosate and Atrazine on Root Meristem of Buckwheat ( Fagopyrum Esculentum Moench )

Herbicides have been extensively used in agriculture but people have not concerned about its adverse effects on plants and animals. The aim of the present study is to analyze the detrimental effects of two herbicides in Fagopyrum esculentum Moench (Variety: VL-7). The root tips were treated with four concentrations viz. 50, 100, 150 and 200 ppm of glyphosate and atrazine at room temperature for 3 hrs. Mitotic indices and chromosomal anomalies were calculated. It was observed that both the herbicides induced different types of chromosomal abnormalities comprising of scattering, precocious movement, stickiness, bridges, laggard etc. along with the increasing doses of herbicides. Scattering and stickiness are most prevalent abnormalities among others. The effect of glyphosate was more toxic than atrazine in the root meristem of Fagopyrum esculentum.