To determine the effects of gamma radiation in inducing mutation on the growth of corn (Zea mays), an experiment using corn seeds exposed in to different rate of radiation (0kr, 10 kr, 30 kr, and 50 kr) was done. Four treatments were prepared using 10 seeds from each of the following different radiation rates. The seeds were planted and were observed for seven weeks. The percent germination and mortality rate, as well as the height (in cm) were obtained. Results showed that the control obtained the highest germination rate and average plant height while the lowest was obtained by the treatment which used the highest irradiation rate (50 kr). From the results it could be concluded that increasing the radiation rate can inhibit the growth in terms of height and lower the percent germination by inducing mutation. As the exposure of the corn seeds to gamma radiation increases, the more it reduces the corns potential for optimum growth and development.
Mutation is defined as the change in the DNA sequence of a gene in an organism that is essentially heritable and permanent. It occurs when the genetic message carried by the gene is altered or damaged (Mendioro et al., 2010). Mutation can either be spontaneous or induced. One way to induce mutation is through the use of mutagens. Mutagens are natural or human made agents (chemical or physical) which can alter the DNA sequence structure of organisms. Examples of mutagens include different types of chemicals and radiation. The use of gamma rays, a type of radiation classified under the ionizing radiations, is commonly used in various experiments in inducing mutation. The use of gamma radiation has diverse effects on the behavior and structure of a chromosome. It can also cause adverse effects on the physiological and biochemical processes of plants. Exposing seeds in high dosage of gamma rays can cause detrimental effects in the growth and germination rate.
Exposure of a seed in higher dose of radiation can cause disturbances on some of its important biological processes such as the water exchange and enzyme activity (Stoeva et al., 2001) and protein synthesis (Xiuzher, 1994). The changes on the morphology, structure and function depends on the strength of the gamma irradiation stress. The parameters used in assessing the effectiveness of radiation in inducing mutations include the percent rate of seed germination and survival of the seedlings. The study aimed to determine the effect of induction of mutation by gamma radiation on the growth of corn (Zea mays). The specific objectives were: 1. to identify the effect of increasing strength of gamma rays on growth of corn (Zea mays) in terms of height, percent germination, and percent mortality; 2. to explain the possible reasons behind the observed effect of radiation on corn.
MATERIALS AND METHODS
In order to determine the effects of radiation on the growth, percent germination and percent mortality of corn (Zea mays), forty seeds were used into four different treatments. The first ten seeds were used as the control (0kr) while the other thirty were irradiated with gamma radiation using different intensities (10kr, 30kr and 50kr). A plot was prepared. Four hills were made in the plot where seeds will be planted. The seeds were planted 5 cm apart on a hill, with each hill representing a specific treatment. The hills were labeled accordingly. For seven weeks, the corn plants were observed. The seed germination (germination time and percent germination) and morphological changes of the vegetative parts of the plant was noted. After weeks of observations, data were consolidated and arranged.
RESULTS AND DISCUSSIONS
As seen in Table 1. results showed that the percent of seed germination (based on the first day of the emergence of the seedlings) under the 10 kr treatment is higher (100%) compared to that of the control (90%), 30 kr (60%) and 50 kr (50 %). Theoretically, the control should have the highest percent germination rate, but since errors which can be attributed from the environment as well as from other physical factors are present, results obtained cannot be avoided. The treatment with the highest irradiation rate (50 kr) has the lowest rate of seed germination. However, in Table 2, results indicated that treatment under the former has the highest percent mortality rate (100 %) while the lowest obtained by the control treatment (40%). In Figure 1, results obtained showed that the treatment with highest average plant height was under Treatment 10 kr.
The final average plant height under this treatment was 28.58 cm compared to the 25.98 cm of control, 20.87 of 30 kr and 6.04 of 50 kr. Again, theoretically, the control should have the highest average plant height but results showed otherwise. Through the obtained data, it can be concluded that exposing seeds to radiation can induce mutation which in the end could affect the growth rate, germination rate as well as the mortality rate of the plant. Observations and data obtained showed that the rate of radiation is inversely proportional to the percent germination and height of corn plants thus proving that percent germination and height decreases as amount or strength of radiation increases, and vice-versa.
The use of gamma radiation can affect some of the important metabolic processes in the plant by inducing mutation. Mutation in return can affect other life processes, such as growth. This can be attributed to the high percent mortality rate of the corn plants under the treatment with the highest exposure to radiation. Increasing radiation exposure beyond 10 kr resulted in retarded growth and abnormal development. Further increased exposure resulted in lethality or high percent mortality rate.
The results and data observed can be attributed to the direct and indirect effect of ionizing radiation to corn plants. If the cells are exposed to ionizing radiation, double-stranded breaks occur along the entire length of the DNA. Mutation occurs if the repair mechanisms reattach the wrong piece of DNA back together, so that a part of the DNA strand goes missing. This may lead to the deletion of important genes or a change in the location of gene within the DNA. (Woodstock, 1965).
Corn exposed to increasing strengths of radiation, resulted to higher probability of the occurrence of mutation. Mutation causes detrimental effects to the cell and might be lethal. Increasing the radiation either qualitatively (strength) or quantitatively (amount), would result have two possible consequences, a single mutation with severe effects which causes malfunctions in the cell and massive mutation with critical effects in the functioning of the cell. There are other possible inferences that could be deduced behind the observed results (Woodstock, 1965).
Figure 1. Average height of corn (cm) with and without exposure to increasing levels of gamma radiation.
SUMMARY AND CONCLUSION
The effect of induction of mutation by gamma radiation was determined through the use of corn seeds exposed to different levels of gamma radiation. Forty seeds were selected and used into four treatment groups (control, 10 kr, 30 kr and 50 kr). For seven weeks, the heights of corn plants were obtained and morphological changes were observed. Also, percent germination and mortality rate were computed.
Based on the results obtained, the treatment with the highest percent germination was the treatment under 10 kr with 100 %, while the lowest was obtained from 50 kr treatment with 50%. Results also showed that the treatment with the highest irradiation rate has the highest percent mortality but with the lowest germination. With these observations, it can be concluded that radiation can affect the growth, germination and mortality rate in corn plants.
The use of gamma radiation can induce mutation and can cause significant changes in the growth, germination and mortality rate of corn plants. Observations and data obtained showed that the rate of radiation is inversely proportional to the percent germination and height of corn plants thus proving that percent germination and height decreases as amount or strength of radiation increases, and vice-versa.
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