IONIZING RADIATION (Gamma rays) AND ITS EFFECT ON PLANT MORPHOLOGY, PHYSIOLOGY, AND CYTOLOGY

IONIZING RADIATION (Gamma rays) AND ITS EFFECT ON PLANT MORPHOLOGY, PHYSIOLOGY, AND CYTOLOGY

1. INTRODUCTION

In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome . These random sequences can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic chemicals, as well as errors that occur during meiosis or DNA replication. They can also be induced by the organism itself, by cellular processes such as hypermutation.

Mutation can result in several different types of change in sequences; these can either have no effect, alter the product of a gene, or prevent the gene from functioning properly or completely. One study on genetic variations between different species of Drosophila suggests that if a mutation changes a protein produced by a gene, the result is likely to be harmful, with an estimated 70 percent of amino acid polymorphisms having damaging effects, and the remainder being either neutral or weakly beneficial.^[4] Due to the damaging effects that mutations can have on genes, organisms have mechanisms such as DNA repair to prevent mutations.

Mutations can involve large sections of DNA becoming duplicated, usually through genetic recombination. These duplications are a major source of raw material for evolving new genes, with tens to hundreds of genes duplicated in animal genomes every million years. Most genes belong to larger families of genes of shared ancestry. Novel genes are produced by several methods, commonly through the duplication and mutation of an ancestral gene, or by recombining parts of different genes to form new combinations with new functions.

Here, domains act as modules, each with a particular and independent function, that can be mixed together to produce genes encoding new proteins with novel properties. For example, the human eye uses four genes to make structures that sense light: three for color vision and one for night vision; all four arose from a single ancestral gene.^] Another advantage of duplicating a gene (or even an entire genome) is that this increases redundancy; this allows one gene in the pair to acquire a new function while the other copy performs the original function. Other types of mutation occasionally create new genes from previously noncoding DNA.

Changes in chromosome number may involve even larger mutations, where segments of the DNA within chromosomes break and then rearrange. For example, in the Homininae, two chromosomes fused to produce human chromosome 2; this fusion did not occur in the lineage of the other apes, and they retain these separate chromosomes. In evolution, the most important role of such chromosomal rearrangements may be to accelerate the divergence of a population into new species by making populations less likely to interbreed, and thereby preserving genetic differences between these populations.

Sequences of DNA that can move about the genome, such as transposons, make up a major fraction of the genetic material of plants and animals, and may have been important in the evolution of genomes.^] For example, more than a million copies of the Alu sequence[An Alu element is a short stretch of DNA originally characterized by the action of the Alu (Arthrobacter luteus) restriction endonuclease. Alu elements of different kinds occur in large numbers in primate genomes. In fact, Alu elements are the most abundant Transposable elements in the human genome. They are derived from the small cytoplasmic 7SL RNA, a component of the signal recognition particle ]are present in the human genome, and these sequences have now been recruited to perform functions such as regulating gene expression. Another effect of these mobile DNA sequences is that when they move within a genome, they can mutate or delete existing genes and thereby produce genetic diversity .

Nonlethal mutations accumulate within the gene pool and increase the amount of genetic variation.^[20] The abundance of some genetic changes within the gene pool can be reduced by natural selection, while other "more favorable" mutations may accumulate and result in adaptive changes.

For example, a butterfly may produce offspring with new mutations. The majority of these mutations will have no effect; but one might change the color of one of the butterfly's offspring, making it harder (or easier) for predators to see. If this color change is advantageous, the chance of this butterfly surviving and producing its own offspring are a little better, and over time the number of butterflies with this mutation may form a larger percentage of the population.

Neutral mutations are defined as mutations whose effects do not influence the fitness of an individual. These can accumulate over time due to genetic drift. It is believed that the overwhelming majority of mutations have no significant effect on an organism's fitness. Also, DNA repair mechanisms are able to mend most changes before they become permanent mutations, and many organisms have mechanisms for eliminating otherwise permanently mutated cells. Beneficial mutations can improve reproductive success.

2. INDUCED MUTATION BREEDING

Plant breeding requires genetic variation of useful traits for crop improvement. Often, however, desired variation is lacking. Mutagenic agents, such as radiation an certain chemicals, then can be used to induce mutations and generate genetic variations from which desired mutants may be selected. Mutation induction has become a proven way of creating variation within a crop variety. It offers the possibility of inducing desired attributes that either cannot be found in nature or have been lost during evolution. Breeding for improved plant cultivars is based on two principles: genetic variation and selection. Induced mutagenesis has been practiced with great success in crop breeding programmes in developing countries since the 1930s (Ahloowalia, Maluszynski and Nichterlein, 2004), but its scope and utility have recently been greatly enhanced and extended by the new molecular-based technology of Targeting Induced Local Lesions in Genomes (TILLING). 

Mutation breeding is the process of exposing seeds to chemicals or radiation in order to generate mutants with desirable traits to be bred with other cultivars. Plants created using mutagenesis are sometimes called mutagenic plants or mutagenic seeds. From 1930–2004 more than 2250 mutagenic plant varietals have been released that have been derived either as direct mutants (70%) or from their progenies (30%).Crop plants account for 75% of released mutagenic species with the remaining 25% ornamentals or decorative plants. However, it is unclear how many of these varieties are currently used in agricultural production around the world, as these seeds are not always identified or labeled as being mutagenic or having a mutagenic provenance. There are different kind of mutagenic breeding such as using Chemical mutagens like EMS and DMS, radiation and transposons are used to generate mutants. Mutation breeding is commonly used to produce traits in crops such as larger seeds, new colors, or sweeter fruits that either cannot be found in nature or have been lost during evolution.

Induced mutations on the molecular level can be caused by:

3. CHEMICALS

Hydroxylamine NH₂OH

Base analogs (e.g. BrdU)

Alkylating agents (e.g. N-ethyl-N-nitrosourea) These agents can mutate both replicating and non-replicating DNA. In contrast, a base analog can only mutate the DNA when the analog is incorporated in replicating the DNA. Each of these classes of chemical mutagens has certain effects that then lead to transitions, transversions, or deletions.

Agents that form DNA adducts (e.g. ochratoxin A metabolites)

DNA intercalating agents (e.g. ethidium bromide)

DNA crosslinkers

Oxidative damage

Nitrous acid converts amine groups on A and C to diazo groups, altering their hydrogen bonding patterns which leads to incorrect base pairing during replication.

4. RADIATION

Radiation in its passage through matter causes the ejection of electrons from atoms on which it impinges. The ejection of electrons may result in both chemical and physical changes in the constituents of cell. These changes are considered to be primarily responsible for the biological effect of the radiation.

Ultraviolet radiation (nonionizing radiation). Two nucleotide bases in DNA – cytosine and thymine – are most vulnerable to radiation that can change their properties. UV light can induce adjacent pyrimidine bases in a DNA strand to become covalently joined as a pyrimidine dimer. UV radiation, particularly longer-wave UVA, can also cause oxidative damage to DNA. Mutation rates also vary across species.

5. GAMMA RAYS AND ITS EFFECT ON MORPHOLOGY OF PALNTS

 Gamma rays belongs to ionizing radiation and are the most effective electromagnetic radiation, having the energy level from around 10kilo electron volts(keV)to several hundred keV. Therefore, they are more penetrating than other types of radiation such as alpha and beta rays. There are several usages of nuclear techniques in agriculture. In plant improvement, the irradiation of seeds may cause genetic, variability that enable plant breeders to select\new genotypes with improved characteristics such as precocity, salinity tolerance, grain yield and quality (Ashraf, 2003). Ionizing radiations are also used to sterilize some agricultural products in order to increase their conservation time or to reduce pathogen propagation when trading these products within the same country or from country to country (Melki & Salami, 2008).

A number of radiobiological parameters are commonly used in early assessment of effectiveness of radiation to induce mutations. Methods based on physiological changes such as inhibition of seed germination and shoot and root elongation have been reported for detection of irradiated cereal grains and legumes. Chaudhuri (2002) reported that the irradiation of wheat seeds reduced shoot and root lengths upon germination. Gamma radiation can be useful for the alteration of physiological characters (Kiong etal., 2008). The biological effect of gamma-rays is based on the interaction with atoms or molecules in the cell, particularly water, to produce free radicals (Kova´cs & Keresztes2002). These radicals can damage or modify important components of plant cells and have been reported to affect differentially the morphology, anatomy, biochemistry and physiology of plants depending on the radiation dose (Ashraf et al., 2003). These effects include changes in the plant cellular structure and metabolism e.g., dilation of thylakoidmembranes, alteration in photosynthesis, modulation of the anti-oxidative system, andaccumulation of phenolic compounds (Kova´cs & Keresztes 2002; Kim et al., 2004; Wi etal., 2007; Ashraf, 2009). From the ultra-structural observations of the irradiated plant cells,the prominent structural changes of chloroplasts after radiation with 50 Gy revealed thatchloroplasts were more sensitive to a high dose of gamma rays than the other cellorganelles. Similar results have been reported to be induced by other environmental stressfactors such as UV, heavy metals, acidic rain and high light (Molas, 2002; Barbara et al.,2003; Quaggiotti et al., 2004). However, the low-dose irradiation did not cause thesechanges in the ultra-structure of chloroplasts. The irradiation of seeds with high doses ofgamma rays disturbs the synthesis of protein, hormone balance, leaf gas-exchange, waterexchange and enzyme activity (Hammed et al., 2008). Due to limited genetic variabilityamong the existing wheat genotypes, Irfaq & Nawab (2001) opened a new era for cropimprovement and now mutation induction has become an established tool in plant breedingthat can supplement the existing germplasm and can improve cultivars in certain specifictraits as well (Irfaq & Nawab 2001)

Several positive mutations have been created in agricultural crops by using gamma irradiations Crops with improved characteristics have successfully been developed by mutagenic inductions (Rehman et al., 1987; Javed et al., 2000; Gustaffson et al., 1971) developed a high yielding barley variety with early maturity, high protein contents and stiff straw by mutation breeding techniques. Khatri et al., (2005) collected three high grain yielding and early maturing mutants by treating seeds of Brassica juncea L. cv. S-9 with gamma rays (750-1000KGy) and EMS.

6. REVIEW ON IONIZING RADIATION (Gamma rays) AND ITS EFFECT ON PLANT MORPHOLOGY, PHYSIOLOGY, AND CYTOLOGY.

The study of the effects of radiation on plants is a broad and complex field. Gamma irradiation was found to increase plant growth and development by inducing cytological, genetical, biochemical, physiological and morphogenetic changes in cells and tissues depending on the irradiation level (Gunckel and Sparrow, 1961). It is one of the important physical agents used to improve the characters and productivity of many plants(Jaywardena and Peiris, 1988, Sharma and Rana,2007). The gamma ray had adverse effect on traits of plants and this depended on plant species or varieties and the dose of irradiation (Artk and Peksen 2006).These effects include changes in the plant cellular structure and metabolism e.g., dilation of thylakoid membranes, alteration in photosynthesis, modulation of the antioxidative system and accumulation of phenolic compounds (Kim et al., 2004, Wi et al.,2005). Mokobia and Anomohanran 2005) found that gamma irradiation were very useful not only for sterilization of medicine but also for the preservation of food and cereals in nutrition and agriculture.

7. EFFECT OF RADIATION ON MORPHOLOGY OF PLANT

7.1 Germination

According to a research conducted by Wilkus,  R.D. (2011)results showed that gamma irradiation can affect the germination of corn (Zea mays L.) seeds. It was observed that different doses of gamma rays have various effects on the total number of germinated seeds and its respective germination rate., the control set-up (0 kr) has 10 out of 10 seeds germinated, and has germination rate of 100 percent. In the 10 kr set-up, 9 out of 10 seeds germinated with a germination rate of 90 percent. In the 30 kr set-up, 9 out of 10 seeds germinated with a germination rate of 90 percent. In the 50 kr set-up, 7 out of 10 planted seeds germinated with a germination rate of 70 percent.

 High stimulatory effect in early growth of maize was observed in 2Gy irradiation group of Kosungjaerae cultivar and in 12 Gy irradiation group of Youngwoljarae cultivar(Kim sung et al, Korean journal of environmental Agriculture ,19-4, pp 328-331).

7.2 Seedling height

Study revealed that there is significant effect of low doses of gamma radiation in certain maize cultivars. The seedling height of maize cultivar kosungjaerae  was found more at the low radiation dose of 2 and 4 Gy(Jae-Sung kim,Young-Keun Lee,Hong-sook Park,Myung-Hwa Back,andDong-Hee Kim,2000).In an publication(Schwartz,1954),a preliminary report was presented describing the effect of high doses of ionizing radiation on germination and growth of maize seeds..

The work of Schmidt and Frolik (1951) and of Beard (1955) has shown that plants of corn (Zea mays L.) grown from seeds treated with appropriate doses of X-rays or thermal neutrons are greatly reduced in stature and survival in comparison with control plants.

7.3 Plant height

According to Hartt and Jones (2006), over a wide range of radiation doses, the frequency of mutation induced by radiation is proportional to the radiation dose Thus, the higher the dosage of radiation, the more evident the expression of morphological changes is observed in the samples. Therefore, low level of radiation produced positive effects such as increase in plant height of corn plants while high level of radiation caused detrimental damage to the corn plants and may result to cell death. Thus, low levels of gamma radiation could be used in agriculture to improve plant cultivation.

 The control group and 10 kr gamma radiation treatment produced the greatest number of germinated seeds and also the highest values for plant height were obtained from the 10kr treatment, only minimal plant height for the 50kr gamma radiation treatment was obtained in maize(Parcon ,2011).

7.4 Root and shoot length

A general reduction in the root and shoot length was reported in maize as the radiation dose increased from 100 Gy to 500Gy, and  the damages caused to a plant by radiation are determined by the amount of energy that is absorbed by the chromosome(Ajayi).

7.5 Grain yield

Mohammad Mehdi Rahimi and Abdollah Bahrani(2009-2010)found that among the two varieties, Zagros cultivar produced more grain yield than Alamot cultivar, grain yield increased in response to application of gamma irradiation, with the grain yield of the crop that no received gamma irradiation being 5% more than control i.e. 25 and 50 Gy gamma irradiation produced the highest grain yield.

There was a more concentrated maturity ,with more ears ready at the time of first harvest in the 1 Gy- and 3Gy treatment in sweet corn cultivar-sunnyvee.(Canadian journal of plant science-vol.48,409-410,1968).

However, Highly significant negative correlations were obtained between high irradiation dosage  and percent kernel set( Pfahler,1967).

 Pfahler(1967) found that the percent kernel set was also reduced by increasing the dosage, no difference was obtained with an increase in dosage from0 to 1 kr,a sharp decrease was obtained by increasing the dosage from 1 to 2 kr with relatively slight decreases observed with further increases in dosages above2 kr and no significant differences were obtained between 3, 4 and 5 kr.

Similarly,Killion et al(1972) found maize variety Golden Bantam was more sensitive than WF9 X 38-11 as measured by a reduction in survival and grain yield when given an acute exposure in the seedling stage on exposure rate below 16R/min.

7.6 Pollen sterility

 The aspects associated with pollen included fertilization ability, kernel set (dominant lethality), fertility, diameter, in vitro germination percentage, and in vitropollen tube length. As indicated by statistical tests, only fertilization ability and in vitro germination percentage were altered by the irradiation treatments.Positive  relation with the pollen sterility and radiation dose was observed in rice (Siddiq and S waminathan,1968),sorghum(Gaud et al.,1970),black gram(Gautam et al.,1992),Trigonella foenum-graecun(Rhaghuvanshi and singh,1974)andVinca rosea(Sudhakaran,1971).

 In maize between 1 and 24 kR, fertilization ability was equal to or above that of 0 kR,above 24 kR, fertilization ability was reduced so that at 40 kR the fertilization ability was about 75% of 0 kR( Pfahler,1967).

Pfahler(1967) observed that the in vitro germination percentage was reduced with increasing dosage, so that at 40 kR the percentage was 75 % of 0 kR, female fertility was the only aspect of female reproduction measured, increasing doses uniformly decreased female fertility to a marked degree so that at 40 kR the female fertility was less than 10 % of 0 kR.

The proportionate increase in the pollen sterility with the radiation dose can be accounted for the cumulative results of the various aberrant meiotic stages, as well as the physiological and of genetic damages induced probably by the breakage of chromosomes through the formation of anti-metabolic agents in the cells(Sudhakaran,1971).

7.7 Leaf size

The effects of γ-irradiation on the biophysical and morphological properties of corn plants investigated with irradiation doses of  0, 1, 1.5, 2.5, 5, and 10 krad showed that corn grains exposed to 1.5 and 2.5 krad showed highly significant changes in all growth parameters like leaf size and chlorophyll content, the obtained results give another support via the biophysical properties for the 1.5 krad irradiation dose to be the most favorable one to improve the plant leaf size(Al-Salhi, M., Ghannam, M. M., Al-Ayed, M. S., El-Kameesy, S. U. and Roshdy, S.2004).

Miah and bhatti(1968) reported that the mean values of the irradiated populations for leaf size in rice  to be almost as same as those of the non irradiated control populations : rather the variance of the irradiated population was greater in comparison to the corresponding controls .

8. REVIEW ON EFFECT OF GAMMA RAYS ON BIOPHYSICAL PARAMETERS

8.1 Chlorophyll content

Gamma radiation induces various physiological and biochemical alteration in plants. The irradiation of plants with high dose of gamma rays disturbs the hormone balance, leaf gas-exchange, water exchange and enzyme activity (Kiong et al., 2008). The effects include changes in the plant cellular structure and metabolism such as dilation of thylakoid membranes, alteration in photosynthesis, modulation of the antioxidant system, and accumulation of phenolic compounds. Based on transmission electron microscope observations, chloroplasts were extremely sensitive to gamma radiation compared to other cell organelles, particularly thylakoids being heavily swollen (Wi et al., 2007).

Furthermore, Kim et al., (2004) have evaluated the chlorophyll content on irradiated red peper plants; their results showed that plants exposed at 16 Gy may have some significant increase in their chlorophyll content that can be correlated with stimulated growth.

The effects of low doses of gamma radiation on water- or Molybdenum-soaked seeds on the photosynthetic apparatus of the resultant seedlings showed  the increase in both the content and stability of the chloroplast pigments, chlorophyll a and b and the carotenoids, moreover, it increased the protein: chlorophyll ratio, the dehydroascorbic, and to a greater extent, the ascorbic acids as well as the photochemical activity of the chloroplasts, the 500 R exposure was generally more effective in producing seedlings better equipped with an active photosynthetic apparatus(Ahmed, . Ashour,  El-Basyouni and Sayed,1976).

8.2 Growth physiological indices

Ionizing radiation like gamma rays can induce some positive effects at lower doses on the crops physiological indices like CGR(Crop Growth Rate) , LAI(Leaf Area Indices),NAR(Nate Assimilation Rate).

·         CGR=(W1-W2   T2-T1)*1    GA

·         LAI= LA/GA

·         (NAR) = LAI × CGR

Where, W, T and GA refer dry matter weight, time and

ground area, leaf area respectively.

The highest LAI and CGR obtained in 25 Gy gamma irradiation with average 4.81 and 25.6, respectively  LAI, CGR and NAR decreased with increasing  gamma irradiation . The best combination in order to obtain the highest LAI and CGR was 50 Gygamma irradiation and Zagros cultivar  The highest NAR was obtained in Alamot cultivar and 50 Gy, gamma irradiation(World Applied Sciences Journal 15 (5): 654-659, 2011).

8.3 Protein content

Kushelevskii and Slifkin (1972)found a cleavage of the peptide linkage after irradiation.At 0.5 Mrad ,the native free organic acids may have been partially destroyed;at higher doses partial radiolysis may occur in the glyceride ester (Dubravic and Nawar 1968)or in peptide linkages(Kushelvskii and Slifkin 1972),which might lead to the liberation of some free fatty acids and amino acids .

Gamma irradiation and interaction between cultivar and gamma irradiation were significant in grain protein percent of wheat cultivar, 25 and 50 Gy gamma  irradiation produced the highest grain protein content, increasing in gamma irradiation more than 50 Gy decreased grain protein about 28% to 67%(World Applied Sciences Journal 15 (5): 654-659, 2011).

The increase in the soluble nitrogen upto a dosage of 2Mrad could be attributed to the partial cleavage of peptide linkage ,however, at higher than 2Mrad,the soluble nitrogen percentage tended to fall,which might be the result of partial elimination of some amino groups from free amino acids (Simic 1968). Nene et al (1975) reviewed the literature about the effect of gamma irradiation on proteins.

8.4 Starch in maize

Many investigators (Akulova et al 1970; Berger et al 1973,1977;El-Saadany et al1976;Korotchenko et al 1968,1973;Yakovenko et al1968)have studied the effect of different gamma ray doses on some physical and chemical properties of corn starch.

 The research indicated that the combination of 20 Gy of gamma-ray and 1 mmol/L of NaN3 is the most effective for mutation inducement of maize calli, three endosperm mutant lines with “super sweet” phenotype were derived from the mutated offspring. By complementation test and DNA sequence analysis, their mutation site was found in exon 14 of gene  sh2 that encodes adenosine diphosphate glucose pyrophosphorylase(African Journal of Biotechnology Vol. 10(76), pp. 17490-17498, 30 November, 2011).

8.5 Proline content in wheat

Biochemical differentiation based onproline content revealed that seedlings irradiated at 100, 200 and 300 Gy, exhibitedproline content of 1.4 mg/g FW, 1.7 mg/g FW and 1.5 mg/g FW, respectively which werenot significantly different as compared to those in non- irradiated seedlings, However, there was no significant difference among the seedlings irradiated with 100,

200 and 300 Gy. In T-65-58-8 genotype, proline contents were slightly increased afterimposing different levels of gamma radiation of seeds as compared with non-irradiatedcontrol , however, in cv. Roshan, proline contents were higher after irradiationwith 100, 200 and 300 Gy as compared to non-irradiated control. A maximum increase in proline contents was observed after 200 Gy dose in Roshan genotype ( BORZOUEI ET AL.,20100).

Gamma radiation was reported to induce oxidative stress with overproduction ofreactive oxygen species (ROS) such as superoxide radicals, hydroxyl radicals andhydrogen peroxide, which react rapidly with almost all structural and functional organicmolecules, including proteins, lipids and nucleic acids causing disturbance of cellularmetabolism (Al-Rumaih & Al-Rumaih, 2008; Ashraf, 2009; Noreen & Ashraf, 2009). Toavoid oxidative damage, plants have evolved various protective mechanisms tocounteract the effects of reactive oxygen species in cellular compartments (Kiong et al.,2008). This defense was brought about by alteration in the pattern of gene expression.This led to modulation of certain metabolic and defensive pathways. One of the

protective mechanisms in the synthesis of osmolytes which is essential to plant growthwas proline synthesis (Esfandiari et al., 2008).

9. EFFECT OF GAMMA IRRADIATION ON GENETIC COMPOSITION OF PLANTS

9.1 Soyabean genetic diversity

Various studies showed that the genetic diversity in soybean (Glycine max L.) germplasm is limited. There is insufficient data on molecular analysis of soybean collections from Africa. The main objectives of the present study were (1) to analyze the genetic diversity and relationships among soybean accessions identified in the DR-Congo gene pool and (2) to determine the effect of gamma radiation on genetic variability. Genomic DNA from several cowpea accessions were analyzed using Inter-simple Sequence Repeat (ISSR) system. The level of polymorphic loci among the soybean varieties was high, varying from 70 to 90% based on ISSR primers used. The soybean varieties analyzed were genetically closely related with several accessions exhibiting similar ISSR amplification profiles. The genetic distance among the soybean accessions varied from 0.00 to 0.46. Some accessions from the International Institute of Tropical Agriculture (ITTA) revealed identical ISSR amplification profile. Seed treatment with gamma-rays at 0.2 KGy (20  Krad) increases the level of polymorphism in progenies by 10%. Low genetic diversity observed within varieties was increased with gamma-ray treatment at 0.1 KGy (10 Krad) and 0.2 KGy (20 Krad) dose.

9.2 Chromosome abnormalities in Allium cepa

Bulbs of A. cepa were treated with different doses of gamma rays. Chromosomal behaviour and antioxidant enzymes status were studied on 3rd and 30th day respectively after irradiation to understand the level of radiosensitivity. A positive correlation between chromosomal abnormalities and antioxidant enzymes related defence mechanism of cell has been established.

9.3 Abnormalities in maize

Maize seeds were pre-soaked in five concentrations of metronidazole and then submitted to four radiation dosages. Part of the seeds was used for cytogenetical analysis and another planted for survival analysis to obtain M2 seeds. Cytogeneticalanalysis showed a radio sensitizing effect of metronidazole mainly in the dosages of 30 and 60 Gy. At 90 Gy, the harmful effect of the radiation hinderedthe analysis of the radio sensitizing effect. The alterations found in M1 reappearedin M2, indicating that those abnormalities are not in their totality due to somatic origin. The use of a radiosensitizing compound can be useful tool for mutant production in plants.

REFERENCES

Abdul Majeed,  Asif Ur Rehman Khan,  Habib Ahmad and Zahir Muhammad ,2010 .Gamma irradiation effects on some growth parameters of Lepidium sativum L.

C E Mokobia and O Anomohanran 2005 J. Radiol. Prot. 25 181, The effect of gamma irradiation on the germination and growth of certain Nigerian agricultural crops.

Fadia El Sherif, Salah Khattab, Ezzat Ghoname, Nashwa Salem and Khaled Radwan,2011.Effect of Gamma Irradiation on Enhancement of Some Economic Traits and Molecular Changes in Hibiscus Sabdariffa L.

Francis A. Haskins,1956, Effects of Irradiation, Maleic Hydrazide, Temperature, and Age on Enzyme Activity in Seedlings of Corn (Zea mays L.).

IAEA,Plant mutation reports.,Vol.2,No,2,2010

Moussa, H. R., 2011. Low dose of gamma irradiation enhanced drought tolerance in soybean. Bulg.J. Agric. Sci., 17: 63-72

Muller, H.J., 1927. Artificial transmutation of the gene. Sci., 66: 84-72

P. L. Pfahler , 1967. Fertilization ability of maize pollen grains 111. Gamma irradiation of mature pollen.

Rahimi,M.M amd Bahrani,A,2011. Effect of Gamma Irradiation on Qualitative andQuantitative Characteristics of Canola (Brassica napus) .World Applied Sciences Journal 15 (5): 654-659, 2011.

Rahimi,M.M amd Bahrani,A,2011. Influence of Gamma Irradiation on Some Physiological Characteristics andGrain Protein in Wheat (Triticum aestivum L.). World Applied Sciences Journal 15 (5): 654-659, 2011

Singh Bhupinderand Datta S. Partha,2010. Effect of low dose gamma irradiation on plant and grain nutrition of wheat.

Stadler, L.J., 1928. Mutations in barley induced by -X-rays and radiations. Sci., 68: 186-7.

W. Ralph Singleton,1954 The effect of chronic gamma radiation on endosperm mutations in maize.

Z. Hegazi and N. Hamideldin , The effect of gamma irradiation on enhancement of growth and seed yield of okra [Abelmoschusesculentus (L.) Monech] and associated molecular changes .