Effects of Radiation on Corn free essay sample

Exposure of corn plants to ionizing radiation such as gamma radiation can induce mutation. The purpose of this study was to determine the effect of varying levels of gamma radiation on growth parameters of Zea mays L. Ten seeds for each level of gamma radiation (0 krad, 10 krad, 30 krad and 50 krad) were planted and tested for the number of germinating seeds and plant height, using a meter stick or ruler. Data were collected for 30 days period and graphs and figures of the data were analyzed. Therefore, it can be inferred that the level of gamma radiation introduced to the plant would have adverse effect on the growth of corn plant; in terms of plant height, number of germinating seeds and its over-all survival rate. Thus, the higher the level of gamma radiation, the shorter the plants will become. Also, low levels of gamma radiation can improve capability of seeds to germinate. INTRODUCTION Mutations can be considered one of the most intriguing topics in biology, particularly in the field of genetics. It is a change in the nucleotide sequence of an organisms DNA, ultimately creating genetic diversity (Campbell Reece, 2008). Mutations are permanent changes in the genetic material. A change in the DNA sequence of a gene 3 can alter the amino acid sequence of the protein coded by the gene. Mutations range in extent from a single nucleotide to a large segment of a chromosome (Campbell, 2008). Mutations may either be spontaneous, or induced by physical and chemical agents (Mendioro, et. al. , 2013). Mutagenesis, the creation of mutation, can occur in various ways. It could be spontaneous which can happen when errors during DNA replication, repair, or recombination are present. Mutations can also be induced by mutagens such as physical or chemical agents which interact with the DNA to cause mutation by altering genetic message. One example of this is the mutagenic radiation which is a physical mutagen that includes non- ionizing radiation such as microwaves, light, radio waves and UV and ionizing radiation such as x-rays, gamma rays, beta and alpha particles and neutrons (Campbell and Reece, 2008). Radiation was the first mutagenic agent known, with its effect on genes was first reported in the 1920’s. There are two major types of radiation—EM spectrum and ionizing radiation. Electromagnetic radiation consists of electric and magnetic waves while the ionizing radiation consists of X-rays and gamma-rays which are energetic enough to produce reactive ions that react with biological molecules (Al-Salhi et al. , 2005). Ionizing radiation produces a wide range of damage to cells due to the production of free radicals of water. Free radicals possess unpaired electrons that are chemically unstable and thus will interact with DNA, proteins, lipids in cell membranes, and other biomolecules. If ionizing radiation passes through a cell in the body, it can cause mutations in the cell’s DNA. This could lead to cancer, or to the death of the cell. The amount of damage in the cell is related to the dose of radiation it receives. The irradiation of seeds with high doses of gamma rays affects certain physiological and biochemical processes which might be vital for the survival of the organism. Previous studies reveal that treatment of seeds with high doses of gamma rays disturbs the synthesis of protein , hormone balance, leaf gas exchange, water exchange and enzyme activity. The morphological, structural, and the functional changes depend on the strength and the duration of the gamma-irradiation stress (Al-Salhi, et al. The extent of the effect of the usage of increasing strength of radiation can be studied using seeds pre-treated with radiation in varying strengths, grown in normal environmental conditions. The study involves subjecting certain number of the model organism, the corn (Zea mays L. ), to increasing strengths of radiation. Corn is a good experimental material for the study because its seeds are widely available. Radiation has been widespread and humans have created artificial sources of radiation which contribute to radiation exposure. Among these are medical testing e. g. diagnostic X-rays, nuclear testing and power plants, and other products e. g. TV’s, smoke detectors, airport X-rays. Radiation, particularly ionizing radiation is proven to cause damage to cells and as a human carcinogenic. Evidences of these come from many different sources, including studies in atomic bomb survivors in Japan, people exposed during the Chernobyl nuclear accident, people treated with high doses of radiation for cancer and other conditions, and people exposed to high levels of radiation at work, such as uranium miners. Radiation induces mutation which could lead to damage in cells, thus, it is essential to acquire insights on the effect of radiation on the growth of organisms. The study aimed to determine the effect of increasing strengths of radiation on plant growth in corn and to verify that the amount of damage in the cell is related to the dose of radiation it receives. The specific objectives were 1. to observe the effects of different doses of radiation on plant growth in terms of height and % germination; and 2. to explain the possible mechanisms behind the observe effect of radiation on plant growth. The study was conducted at the Institute of Biological Sciences, University of the Philippines Los Banos, College, Laguna from July 15, 2013 to Sept 20, 2013. MATERIALS AND METHODS The experiment worked the effect of radiation on the growth and development of the corn plant. This made use of forty corn seeds with four different set- ups. In each set-up, ten Zea mays L. seedlings were planted in a plot and were treated with different dosage of gamma radiation- 0 krad (control), 10 krad, 30 krad and 50 krad. For thirty days, the corn plants were observed every Monday, Wednesday and Friday. August 28 and September 27 served as replacement for holidays while August 20, 23 and Sept 9, 20 were declared no classes. The plant average height in every set- ups was measured using a meter stick or ruler by the assigned person in each day. The data were recorded and compiled. Based on this data, percent germination and percent survival were calculated using these formula. % survival = Total no. of plants observed= 20 Results and Discussion Results showed that gamma irradiation can affect the germination of corn (Zea mays L. ) seeds. It can be observed that different doses of gamma rays have various effects on the total number of germinated seeds and its respective germination rate. As shown in Table 1, the control set-up (0 kr) has 20 out of 20 seeds germinated, and has a germination rate of 100 percent. In the 10 kr set-up, 20 out of 20 seeds germinated with a germination rate of 100 percent. In the 30 kr set-up, 18 out of 20 seeds germinated with a germination rate of 90 percent. In the 50 kr set-up, 0 out of 10 planted seeds germinated with a germination rate of 0 percent. Table 1. Percent Germination of Corn Plants. Plant Treatment Number of Germinated Seeds % Germination Control 20 100 10 krad 20 100 30 krad 18 90 50 krad 0 0 A positive tendency for the seed to germinate can be observed if a low or no dosage of gamma radiation was introduced to the seedlings. However, high levels of gamma radiation had an adverse effect on seed germination. Furthermore, very high levels of gamma radiation may lead to cell death which is a result of the inability of the DNA to repair breaks caused by mutagens such as gamma radiation. In relation to these results, another relationship can be determined. It can be observed that an increase in dosage of gamma rays irradiated decreases the survival rate of corn plants. As shown in Figure 2, the control set-up has a survival rate of 90 percent. The 10 krad set-up has a survival rate of 65 percent. The 30 krad set-up has a survival rate of 40 percent. Meanwhile, the survival rate of the 50 krad set-up cannot be defined since it has a zero percent germination rate. Table 2. Percent Survival of Corn Plants. Plant Treatment Number of Alive Seeds % Survival Control 20 65 10 krad 20 40 30 krad 18 33 50 krad 0 0 The relationship between varying doses of gamma irradiation and the germination and survival rates of corn plants can be observed in Figure 1. Figure 1. % Germination and % Survival of Corn Plants under gamma radiation. Table 3 shows that the corn plants treated with 10 krad of gamma radiation has the highest mean height () followed by the control with a mean height of cm. The 30 krad treatment yielded a height cm while the 50 krad treatment had the shortest height among the treatments with a height of cm. Table 3. Average height (cm) of Zea mays L. for 8 weeks. TREATMENT Week CONTROL 10 krad 30 krad 50 krad 1 2 3 33. 04 33. 35 21. 25 7. 57 4 47. 33 48. 37 25. 33 0 5 62. 64 61. 14 43. 38 0 6 69. 83 74. 48 50. 15 2. 95 7 51. 48 62. 17 40. 07 0 8 52. 61 60. 73 45. 7 0 MEAN VALUES In order to discuss the effect of gamma irradiation on the germination and development of corn, it is a must to discuss first the mechanism of gamma irradiation. Photons of electromagnetic radiation are oscillating pulses of energy, without electric charge, and therefore they continue along a straight line in their passage between atoms of a material. When a photon collides with a charged atom particle, however, it induces the particle to oscillate and therefore yields up some or all of its energy. The effects of a collision between a gamma- or X-ray photon and an atomic particle are various and depend on the energy of the photon (Purdom, 1963). If the photon is of relatively low energy (which was the kind of ionizing energy that was used in the experiment) and it collides with a planetary electron, the electron may absorb the energy of the photon. This additional energy may drive the electron right out of the atom and so ionise it. The action of a low-energy electron and the later consequences are also the same, chemical action or fluorescence, and heat production (Purdom, 1963). At the molecular level ionizing radiation causes the ionization of water and other molecules around the DNA, forming free radicals. These free radicals can then attack the structure of DNA with its unpaired electron (Starr, 2000). Considering the radiation chemistry of the solutions, the main difficulty arises from the high number of reactive species which are formed during the primary processes. In water, at least five reactive species are formed: H2O H2O*, H2O+, e-, H†¢, †¢OH Also, the doses required to produce appreciable numbers of free radicals which can be detected in dry materials are in the same dose range used for biological experiments in the same material. For instance, in dry seeds we can detect radicals with doses as low as 5 kr, where 10 to 80 kr is the biological range (Conger, 1963). This means that using ionizing energy with even low dosage in experiments will still ensure the formation of free radicals in the irradiated cells. This explains the likelihood of mutation upon irradiating a cell or an organism with ionizing energy. At the cytological level ionizing radiation produces two readily discernible effects: chromosome aberrations and mitotic inhibition (Haber, 1972). During the normal mitotic cycle in unirradiated cells, individual chromosomes seem to maintain their integrity without breakage or rearrangements. After irradiation, however, chromosomes or strands of chromosomes can break at various points along their lengths. At the subsequent telophase an acentric fragment is unable to move to either of the newly constituted daughter nuclei. Such chromosome fragments remain outside of the nuclei and their genes are lost to further progeny of the original, irradiated mother cell. This type of deletion is the simplest type of chromosomal aberrations that leads to gene deficiencies in daughter nuclei produced by mitosis after irradiation. Another type of chromosomal abnormality results from rejoining of two different broken chromosomes in such a manner that the newly formed structure has two centromeres. If the two centromeres happen to move to two opposite poles at anaphase, then the chromosomal material becomes stretched between them to produce a chromosome bridge across the cytoplasm the genes on this extranuclear chromosome bridge are lost at the progeny of the irradiated cell (Haber, 1972). SUMMARY AND CONCLUSION The effect of varying radiation was determined by exposing corn seeds to different radiations: 0 krad, 10 krad, 30 krad, and 50 krad. There were twenty seeds per treatment, and each set-up was planted in the same place and subject to the same amount of sunlight and water. Within eight weeks, the growth, in terms of height was measured and the % germination and % survival were calculated. Results showed that the control set-up yielded the highest value of % germination and survival and average height (100%, 65, cm) compared to the treated corn seeds. The corn seeds treated with 10 krad radiations had 100% germination, 40 % survival and the average value for height was cm, while corn seeds treated with 30 krad had 90 % germination, 33 % survival and average height of cm. Corn seeds treated with 50 krad radiation yielded 0% germination and survival with average height of cm. It is highly recommended that the experiment must be conducted in a well-maintained environment, that is, free from destructive factors. Some of the factors that contributed to the possible errors in the results of the experiment were environmental factors (e. g. wind, rain, and weather), physical agents (e. g. roaming animals), inappropriate soil type, inaccurate measurement of the plant height and lack of maintenance.