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Mutations in plants can be induced using acute irradiations such as X-rays, Y-rays and gamma rays among other forms of radiations. However, there is normally a relative difference in the modes of action in respect to the rays irradiated on certain plants. Notably, providing plants with varieties of genes can help to improve the productivity of a given crop. As a result, gamma rays have been used to enhance convectional breeding which results in genetic variability. According to Khan et al., (1982), mutation breeding can effectively take place in plants when they are exposed to gamma radiations. This induces genetic variability. Indeed, plants can also be exposed to gamma radiations at germination stage, which implies that seeds have to be treated with gamma radiations.
Gamma rays have been used in plant breading. Plant researchers have over decades carried extensive researches on plant breeding using radiation to the extent of the plant gene slicing using gamma rays. Radiation breeding is a condition where plants are exposed to a certain radiation. This results into what is known as mutagenic breeding. Researchers have established that both X-rays and gamma radiations have varied effects when they are exposed to plants. Moreover, various researches have been done to show the effects of gamma rays on the emergence of seedling, survival, height of seedling, height of plants, as well as the days the plant takes to flower up to maturity (Khan et al., 1982). Generally, gamma radiations have been used to change plant’s physiological characteristics with the main aim to improve the quality of the seedling, as well as raise the amount of yield. To fully understand the effects of gamma radiations on plants, this research paper will take an example of two commercial varieties of cotton (G. hirstutum viz) MNH93 and NIAB78.
Gamma Radiation and Plant Genetics
Mirza and Mirza (1986) observed that gamma rays play a major role in shifting the features in various genotypes of cotton. Essentially, deletion of mutagenesis is used to explain how various species of plants are affected by gamma radiations. When such deletions and chromosomal deficiencies occur due to radiations, the resultant is that the irradiation of seeds and pollen takes place. The combinations takes place due to radiation caused by the gamma radiation exposed to the plants. There are other aspects of plant genetics which also takes place when there are large deletions caused by radiations.
According to Vizir et al. (1994) Arabidopsis which involves studies in pollination as a result of irradiated pollen, there is a mixture of aborted and normal seeds which results from the correlation with gamma radiations. Notably, seed abortion is a result of endosperm development which is normally caused by mitotic arrest which takes place in the cells which carry unrepaired inter-strand cross-links. On the same, Bennet et al. (1993) argues that seed abortion may also be caused by unbalanced gene dosage which may be possible in a situation where one of the two copies of gene or both have been deleted as they play supplementary role. This is the best example of the condition where gamma radiations can damage the crops instead of modifying them. According to Ashburner (1989), heterozygotes carry large number of deletions which may affect a particular genomic region. This is evident from the Drosophila which explains the situation where there are hererozygous deficiencies that are dominant in lethality. There are also other cases where the mutation process in heterozygotes may not be viable as the deletions of genes in the regions may not take place as expected.
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Effects of Gamma Radiation on Plants
Mainly, exposing plants to gamma radiations changes their physiological characteristics which include the heights, time of germination, quality, and amount of yield, as well as the flowering period. However, depending on the dosage of gamma radiations, plants can be modified or damaged. Therefore, radiation dose will determine whether the plant cells will be modified or not. This is because plants will respond differently in terms of anatomy, morphology, biochemistry, as well as physiology (Abdel-Hady, 2008). At the same time, there changes that are more pronounced in terms of the alteration in the plant cellular structure, as well as metabolism. Plant processes, such as photosynthesis, anti-oxidation system, among others are modified as a result of exposing them to gamma radiations (Khan et al., 1982). So, the plant genes are changed bringing in new characteristics of the plant, which are different from others which have not been exposed to the same radiation.
Gamma radiations are responsible for inducing deletion of mutations in plants. About a quarter of the induced putative deletions can thrive in the diploid heterozygote. Nevertheless, there is also a large proportion of deletions which forms the dominant lethality, especially in the diploid heterozygotes where they can only survive. This occurs in situations where the dose of radiations exceeds the optimum amount needed to modify the plant. There are two common types of deletion events that take place in plants as a result of the exposure to gamma rays. These include the terminal and internal deletions. In case of terminal deletions induced by gamma irradiation, there must be a correlation between the mutation frequency and the genetic length (Al-Rumaih, 2008). On the other hand, internal deletions are not marked by any form of correlation, but may affect the physiology of the plant.
Materials and Methods
Two commercial varieties of G. hirstutum viz MNH93 and NIAB78 are used in this research to establish the effects of gamma radiations on cotton. They were treated with Cobalt-60. The seedlings were planted at a distance of about 75cm between the plants, as well as row to row. Plants were also protected from any form of external interference. The main aim was to examine the effect of irradiation of gamma on the growth of the plant, survival, flowering and maturity (Khan et al., 1982). Each plant was assessed and analyzed from plant to plant to identify the variance in plants’ characteristics and identify how gamma irradiation was responsible for the change in genes in the respective plants.
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There were no significant differences in terms of the rate of germination, survival and days of flowering. Both varieties responded similarly when exposed to gamma irradiations. When the dosage of gamma irradiations is increased, the plant begins to show changes. It is worth noting that a plant may be modified or damaged depending on the quantity of the radiations used. This was in accordance with Khan et al., (1982) research that showed that reduction in the emergence of seedling was affected by the amount of radiations exposed to it. The effects of other activities in plants, such as mitotic ad oxidative phosphorylation, were also to some extent responsible for the changes in plants apart from the exposure to gamma irradiations. The increase in the doses of gamma irradiation was to some extent lethal to survival of the plants at the certain level (Ashraf, 2009).
It was noted that MNH93 could only survive well at 30 %, while NIAB78 did best at 43.33 % of gamma radiations. This effect was attributed to the increase in frequency of chromosomal aberration, as well as rise in the levels of inhibition of recovery mechanism (Mirza & Mirza, 1986). On the same, the height of the seedling was also dependent on the amount of gamma radiation that was exposed to individual seedlings. However, at the certain levels of gamma irradiations, the height of the seedling was also observed to decrease. This implies that gamma irradiations have a direct effect on the height of the seedling. When seedlings are treated with gamma irradiations, RNA or protein synthesis is activated, which takes place during the initial stages of germination. However, the rate of germination is not significantly affected by the gamma irradiations. Nevertheless, the root and shoot length are affected, especially when the dose of gamma irradiation is optimum.
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As analyzed above, gamma irradiation can cause variability in plants genetics that make it possible to select new genotypes which have improved the plant breeding. This is simply because gamma rays form one of the ionizing radiations within the electromagnetic radiation. Due to its energy level of 10 kg electron volts (KeV), they have higher penetrating power than any other type of radiation. This makes their use in agriculture, especially in plant breeding, more useful. Therefore, exposing seedling to gamma irradiation, such as cotton seeds among others will result in seedling with improved features in terms of heights, rate of germination, flowering days, and amount of yield, as well as maturity. As a result, the plant precocity, tolerance to salinity, quantity of yield, as well as the quality is improved through the use of this radiation. Thus, gamma radiations are used to change the physiological features in plants, which is as a result of changes in plant genes.
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