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Effect of Increasing Irradiation Dosage on Corn Growth

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The Effect of Increasing Irradiation Dosage on the Rate of Growth and Germination of Corn (Zea mays L.)1

  • Amarie S. Aguirre

 

ABSTRACT

The effects of mutation induced by irradiation to plants were determined. A plot with four hills of plants was planted and three hills of plants were exposed to radiation, 10 krad, 30 krad and 50 krad respectively. The height of the plants was measured and observed. Results showed that plants exposed to radiation have a shorter height than that of the control set up and the plants exposed to radiation has decreasing height as the dose of radiation increases. High percent germination was observed on the control setup. It is concluded that radiation has effects on the growth and germination of plants and high amount of radiation decreases the germination and survival rate of plants. This is because radiation is a kind of mutagen and it altered the growth of the plants by affecting the plants’ chromosomal structure. Thus, an increase in the dosage of radiation makes the plant more unlikely to survive.

INTRODUCTION

Mutations are considered as permanent alterations in the primary encoding nucleotide sequence of an organism, which can be caused by either unrepaired damage to DNA or RNA, errors in the process of replication, or insertion or deletion of DNA segments. (Ramirez, et al., 2005). Mutations can be silent, beneficent, or deleterious: silent mutations have no effect on the organism’s phenotype, beneficent mutations have positive effects on the phenotype that can increase survival, and deleterious mutations have dire and often fatal effects on the organism’s phenotype.

Radiation from the sun is a type of mutagen that can be a threat to organisms though it is the main source of energy. Mutagens are factors that can induce mutation. (Rabago, et al., 2003). Mutations can be induced in an organism, either by use of chemical agents such as hydroxyl amines, alkylating agents, or agents that cause oxidative damage; or by radiation via UV or gamma irradiation. Short wavelength radiation can penetrate DNA and break the bonds within. (Barh & Srivastava, 2008). Induced mutations are most often deleterious in nature for the organism’s phenotype, and can cause decreased growth, infertility, or death of the organism.

The biochemical effect of radiation on an organism depends upon the type of the radiation that was used: in ionizing radiations, such as gamma rays, the radiation ionizes water into H and OH ions that can produce secondary free radicals, that can in turn damage or modify cellular components, especially DNA and RNA structures, that can induce mutation; while in non-ionizing radiations, such as UV rays, UV light can induce covalent joining of adjacent pyrimidine DNA bases into pyrimidine dimer, and can also cause oxidative damage to DNA, inducing mutation. The severity of mutagenic effect of radiation on the organism would ultimately depend on the dose of radiation the organism received. (Wang, Gorsuch, & Hughes, 1997)

Zea mays has been used as a basis model organism for basic research, and is the subject of a multitude of investigations such as domestication, evolution, physiology, epigenetic, pest resistance, inheritance, and comparative genetics, and one of the most thoroughly researched system; and is fitting for studying the effects of radiation in plants. (Scanlon & Strable, 2009) The present study was conducted to determine the effects of increasing doses of radiation on corn plants, specifically, to determine:

1) the effect of increasing doses of radiation on the survival of corn plants;

2) the effect of increasing doses of radiation on the growth rate of corn plants; and

3) to elucidate and conclude the possible mechanisms involved in correlating increasing doses of radiation and corn plant growth and development.

MATERIALS AND METHODS

To induce mutation on the seeds of corn, irradiation was done at varying doses. Per treatment, ten seeds are used. A hill was made for each plot with different doses of radiation where each seed was planted 5cm apart. On the first hill, the control set up was placed. Then on the other three hills, plants exposed to increasing dose of radiation was placed, 10krad, 30krad and 50krad respectively. There were two replicates per set-up. The height of each plant was observed and recorded for three months every Monday, Wednesday and Friday. percent survival and percent germination were also computed and recorded.

RESULTS AND DISCUSSION

In Table 1, the results were tallied for the number of surviving plants that were observed, as well as their average length of growth, and grouped according to the amount of radiation received. Both 0 kRad and 10 kRad plants had a 50% survival until the 48th day of observation, while both 30 kRad and 50 kRad plants had a 0% survival until the 48th day of observation, with the 30 kRad plants dead at the 13th day of observation, and while the 50 kRad plants dead at the 6th day of observation. The 10 kRad plants achieved a higher length of growth at the 48th day of observation when compared to 0 kRad plants, measuring at an average of 91 cm for 10 kRad plants and 78 cm for 0 kRad plants.

Table 1. Number of plants observed and their average height grouped according to the amount of radiation received by their seedlings.

Date

Observation Day

0kRad

10kRad

30kRad

50kRad

# of plants observed

ave.height (cm)

# of plants observed

ave.height (cm)

# of plants observed

ave.height (cm)

# of plants observed

ave.height (cm)

Oct15

1

9

9.41

5

10.1

3

6.97

3

2.17

Oct17

3

10

12.5

4

18

3

7.67

3

3.5

Oct20

6

8

21

4

23.9

2

7.3

0**

-

Oct22

8

8

22

4

23.5

2

6.5

-

-

Oct24

10

8

23.44

3

29.75

1

7.5

-

-

Oct27

13

8

26.19

4

31.65

1

7.5

-

-

Oct29

15

8

25.25

3

44.83

0**

-

-

-

Oct31

17

8

33.6

3

45.4

-

-

-

-

Nov3

20

7

18.43

3

27.67

-

-

-

-

Nov5

22

7

22.43

3

30

-

-

-

-

Nov7

24

7

26.41

3

35.1

-

-

-

-

Nov10

27

7

42.7

3

55.5

-

-

-

-

Nov12

29

7

44.11

3

55.3

-

-

-

-

Nov14

32

6

47.88

2

68.4

-

-

-

-

Nov17

34

6

58.63

2

68.25

-

-

-

-

Nov19

36

6

66.08

1

72

-

-

-

-

Nov21

39

6

72.27

1

79.5

-

-

-

-

Nov24

41

6

74.13

1

84

-

-

-

-

Nov26

43

6

76.07*

1

86*

-

-

-

-

Nov28

45

6

78

1

88

-

-

-

-

Dec1

48

6

78

1

91

-

-

-

-

                   

*Values were undetermined, assumed to be the average between two observed values.

**0 value means no alive plants were observed.

To simplify the results, we can separate the plant survival and their average height, grouped via the dose of radiation that they initially received. Figure 1 shows the number of plants surviving until the last observation day. Again, both 0 kRad and 10 kRad plants had a 100% survival until the 48th day of observation, while both 30 kRad and 50 kRad plants had a 0% survival until the 48th day of observation, with the 30 kRad plants dead at the 13th day of observation, while the 50 kRad plants dead at the 6th day of observation.:

Figure 1. The number of surviving plants until the last observation day according to the amount of radiation received.

Figure 2 shows the average length of growth of surviving plants until the last observation day according to the amount of radiation received. Again, the 10 kRad plants achieved a higher length of growth at the 48th day of observation when compared to 0 kRad plants, measuring at an average of 91 cm for 10 kRad plants and 78 cm for 0 kRad plants. It can be noted that the 0 kRad and 10 kRad plants have a similar pattern and rate of growth observed across time, differing only in the maximum average length achieved. The length of growth of 30 kRad and 50 kRad plants were much less than the 0 kRad and 10 kRad plants before their death.

Figure 2. The average length of growth of surviving plants on observation days based on the amount of radiation received.

Radiation excites the electrons making it reactive. These overactive electrons, in turn, knock other electrons out of their orbital. This results to chromosome breaks. The frequency of mutations produced is directly proportional to the amount of radiation. (Sinnot, Dunn, and Dobzhasky, 1950). So, more genetic changes are present in increasing radiation dosage, therefore decreasing their ability to survive. However, the effect of radiation is not extensive enough to wreak variable alterations in the corn plants. The dosage is small, and the cells can adapt to the changes inflicted to them. As we can see, the trends of 0kRad and 10kRad have a similar pattern and rate of growth observed across time, differing only in the maximum average length achieved. But the length of growth of 30 kRad and 50 kRad plants were much less than the 0 kRad and 10 kRad plants before their death. From all the data we have gathered and inferred from above figures, thus, we can validate our stated hypothesis that as the increasing dosage of radiation increases, the survival rate and the height of the corn plants decreases.

The possible sources of errors for this study are: first, the maintenance of the plant during the research. Second, there are many grasses and pests in the area that may have caused competition with the plant. And lastly, the human errors made during the period of measurement. These errors caused slight to big modifications. These errors though did not greatly affect the results obtained because the trend is still observable.

SUMMARY AND CONCLUSION

The effect of increasing irradiation dosage on the growth rate and survival capability of corn plants was studied and results showed that as radiation increases, the height of the corn plants decreases. It can be inferred that radiation has effect on the growth and germination of plants. Radiation has properties that can damage the cell and eventually damage the chromosomes and the DNA. This damage in the chromosomes and DNA results to mutation. Therefore, it can be concluded that increasing radiation dosage greatly affects the growth of plants by decreasing the height of corn.

It is also concluded that in the presence of tolerable amounts of radiation, there is not much significant alterations in the normal growth of corn since there is still excision of the errors in the chromosome structure brought about by the natural mechanisms in the cells that can adapt to the changes inflicted to them.

However, this experiment should be subjected to further studies. It can also be recommended that this experiment should be tested to different kinds of plants and different kinds of radiation to fully understand and explain mutation and effects of radiation not only to the growth of the plants and germination but also on the other processes that can be affected by radiation.

Literature Cited

Barh, D., & Srivastava, H. (2008). Genetics : Fundamentals and Applications.New Delhi, India: International Book Dist.

Rabago, L.M. et al. 2003. Functional Biology: Modular approach. Quezon City: Vibal Publishing House, Inc. p. 401.

Ramirez, D.A., M.S. Mendioro and R.P. Laude. 2005. Lectures in Genetics. 8th ed. San Pablo City, Laguna: 7 Lakes Printing Press. p. 126, 139.

Scanlon, M., & Strable, J. (2009, October). Retrieved December 8, 2014, from http://www.pubfacts.com/: http://www.pubfacts.com/detail/20147033/Maize-Zea- mays:-a-model-organism-for-basic-and-applied-research-in-plant-biology

Sinnott E.W., L.C. Dunn and T.H. Dobzhansky. 1950. Principles of Genetics. USA: McGraw-Hill Book Company, Inc. p. 291-296.

Wang, W., Gorsuch, J. W., & Hughes, J. S. (1997). Plants For Environmental Studies. Florida, USA: CRC Press LLC


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