Effect of Ionizing Radiation on the Germination, Growth and Development of Corn (Zea mays L.)
Alexis A. Parco
BIO30 Group 1 Sec. A-6L
September 27, 2012
Corn seeds pre-exposed to 10, 30, and 50 kiloRads (kR) of radiation were grown in plots for almost 7 weeks. Four different setups – 10kR, 30kR, 50kR and the control, each with 10 corn seeds initially planted – were observed three times a week (during Mondays, Wednesdays and Fridays), and the height of each growing corn was measured (in cm) together with the germination rate (%Germination). The results obtained showed that the growth of the corn in terms of height and the percent of germination in corns were generally inversely related to the amount of radiation they were exposed to. Though the final average height computed showed 28.4 for the 10kR setup and only 24.65 in the controlled, it can be referred to the table that the average height and the germination rate of the latter were the greatest among the others’, in general. Referring to the data from the 17th of August and 3rd of September, for instance, it can be seen that the average height for the 10kR treated corn were 10.16 and 29.3, respectively, those of the 30kR were 4.064 and 0, while those for the control setup 13.208 and 40.4. On the other hand, the 50kR corns exhibited noticeable late sprouting and early death with an average height of 0 during the last day of observation. It has obtained the least height and germination rate in the overall. Hence, increasing the exposure of corn to radiation interferes with its growth and at the same time decreases the germination rate of such a plant by means of inducing the process of mutation.
Mutations are changes in the genetic information of the cell (or even a virus) which hold responsible for the very large diversity of genes found among organisms. It is the ultimate source of new genes.
The existence of mutations can be accounted for several ways. Though rarely occurring, errors during the DNA replication process or recombination can lead to changes such as deletions, insertions, base-pair substitutions, as well as to mutations affecting the longer stretches of DNA. For instance, if a wrong base is added to the accumulating chain during the replication process, that base will surely be mismatched with the corresponding base on the opposite strand. Certain systems will then be responsible for repairing such errors. Otherwise, the incorrect base will further be used as a template in the next round of the mentioned process, resulting in a mutation. These mutations are called spontaneous mutations. Considering the estimates made by experts to the rate of mutation during DNA replication for both E. coli and eukaryotes, the numbers turned out to be similar. That is, about one nucleotide in every 1010 is altered, and the change is passed in to the next generation of cells.
A number of physical and chemical agents, called mutagens, interact with DNA in ways that cause mutations. Upon H. Muller’s discovery that X-ray caused genetic changes in fruit flies, is the recognition of the hazard of such a discovery. That is, X-ray and other forms of high-energy radiation pose hazards to the genetic material of not only the laboratory specimens but also to people. Mutagenic radiation includes physical agents such as the ultraviolet (UV) light, which cause disruptive thymine dimers in the DNA. Chemical agents or chemical mutagens such as those which interfere with the correct DNA replication by inserting themselves into the DNA causing distortion to the double helix are also included (Campbell, et al,. 2007).
The chemical basis of radiation damage is classified as that of the ionizing radiation. There is a possibility that electron from atoms and molecules in the path of gamma particles or rays be removed thus, leading to the formation of ions and the short-lived but highly reactive radicals. In the case of the corn, water radicals...
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