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Effect of Increasing Amount of Radiation on Corn (Zea mays)

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The Effect of Increasing Amount of Radiation on the Plant Growth of Corn (Zea mays)1

  • Pamela Ysabel B. Mendoza

 

ABSTRACT

The effect of radiation on the growth of corn plants was determined by planting exposed and unexposed seeds. It is expected that plants exposed to higher radiation will exhibit hindered growth. 20 corn seeds were left unexposed to radiation (control) while 60 seeds were exposed to different doses of gamma radiation— 20 seeds were exposed to 10 krad of radiation, another 20 to 30 krad, and 20 more were exposed to 50 krad. The highest percent germination (50%) was found in the control group while the lowest (15%) were found in the groups of seeds exposed to 30 and 50 krad of radiation. The highest percent survival (60%) was also found in the control group while the lowest were also found in the groups of seeds exposed to 30 and 50 krad radiation. Thus, low doses of gamma radiation may enhance growth but high doses of radiation inhibit plant growth and are even lethal.

INTRODUCTION

Changes in an individual which can be passed on to offsprings and are most likely permanent are called mutations. There are mainly three kinds of mutations: mutations due to the change in number of chromosomes, mutations due to aberrations in the structure of the chromosomes, and mutations in the genes. Mutations due to the change in the number of chromosomes are due to the addition or deletion of one or several (aneuploidy) or whole sets of chromosomes (euploidy). Mutations due to structural aberrations are due to deletions, duplications, inversions or translocations of specific sections of the chromosome which cause changes in alignment of loci during the pairing of bivalents. Gene mutations are changes in the nucleotide pairs either by substitution with a different nucleotide or by the addition or deletion of one or several nucleotides (Ramirez, et al., 2013).

Gamma radiation is super high energy photons which can trek vast expanses in light speed without colliding with electrons and can cause ionization during electron capture. The small size and high energy of the photon makes gives it an ability to penetrate deeply into thick barriers therefore, one must be feet-deep in concrete of protected by a few inches of lead to be shielded from gamma radiation (Fire, 2009).

Gamma radiation is a form of ionizing radiation which causes the formation of free radicals from the water molecules inside plant tissues. These free radicals can cause damaging effects to the organic molecules of the plant especially the nucleic acids since they are larger molecules compared to others found in the cell. The depolymerization of polysaccharides may also occur along with inactivation and deformation of enzymes due to the reduction of disulfide bonds. Smaller molecules like free amino acids may also be affected via deamination. (Somogyi, et al., 1996).

This exposure to gamma radiation may cause mutation in an individual by damaging the sugar phosphate backbone of the DNA strand and may lead to certain structural aberrations in the chromosome. Frameshift mutations may also occur if ever the radiation would induce the loss of one or several nucleotides (Ram, 2010).

Past studies of the effect of radiation on plant growth were conducted by Sparrow, et al. (1970) and they have concluded that the chance of survival of the plant from irradiation is different with every species. They also found that cereal crops are among the most susceptible to radiation with its yield decreasing by 50% depending on the dose of gamma radiation applied from 1kR to 4kR (Wang, et al., 1997).

It is expected that a greater dose of radiation will cause inhibition of the growth of the corn plant. This study investigated the effect of gamma radiation on plant growth by growing the seeds and comparing the measured heights. Investigation and observation of the corn plants occurred from October 15 to December 1, 2014 at the Institute of Biological Sciences, University of the Philippines Los Baños. The objectives of this study were

  1. To describe the effect of gamma radiation on the growth of corn plantlings; and
  2. To explain how radiation affected the growth of corn.

METHODOLOGY

To examine the effect of radiation on the growth of corn plant, 60 corn seeds were exposed and irradiated with gamma radiation of different amounts. 20 of these were exposed to 10 krad of radiation, 20 more exposed to 30 krad and another 20 exposed to 50 krad. 20 other seeds served as control and were not exposed to radiation.

These seeds were then planted and its height was measured every Monday, Wednesday and Friday each week from October 15 to December 1, 2014. Percent germination was computed by dividing the highest number of plants observed by 20 and the percent survival was computed by dividing the number of plants on the last day of observation by the highest number of plants observed. A graph showing the growth curve, percent germination and percent survival of corn plants exposed to each dose of radiation was then plotted and analyzed.

RESULTS AND DISCUSSION

As seen in Table 1 in the appendix and the growth curve in Figure 1, corn plant which achieved the greatest height (89.00 cm) was exposed to 10 krad of gamma radiation while the second highest average height (80.88 cm) was not exposed. The highest average height attained by the plants exposed to 30 krad was 8.00 cm while it was 3.50 cm for the plants exposed to 50 krad of radiation. The greater mean height achieved by the group of seeds exposed to 10 krad of radiation could be due to some stimulation on the chloroplasts and caused modifications on the chlorophyll pigmentation. This could have indirectly boosted the initial growth of the plant (Kim, et al., 2004).

Figure 1. Growth curve of corn plants as a result of increasing radiation dose.

Figure 2 shows that the dose of gamma radiation applied clearly affected the percent germination of the corn seeds. The control group had the highest number of germinating seeds (50%) while seeds exposed to 10 krad of radiation only had 25% of seeds germinate. Seeds exposed to 30 and 50 krad both had only 15% of their seeds germinate. As stated by Somogyi, et al. (1996), this could be due to the destruction of the DNA molecule which is the pattern for the construction of proteins and other biomolecules necessary for the growth of the plant.

Figure 2. A bar graph showing the percent germination of corn seeds for each dose of gamma radiation.

Percent survival of the plantlings also varied with the dose of radiation applied (Fig. 3). By the end of the testing period, 60% of the seeds that germinated are still alive and growing in the control group while only 20% survived with the seeds exposed to 10 krad of radiation. None of the seeds survived upon exposure to 30 and 50 krad of radiation. None remained of those plants exposed to 30 krad about 19 days after the start of the observation period while the plants exposed to 50 krad of radiation were terminated in as early as about 5 days after the start of observation (Figure 1). The possible explanation of this could be the inability of the corn plant to properly regulate the mutations brought about by the high doses of radiation.

Figure 3. A bar graph showing the percent survival of corn plants for each dose of gamma radiation after 47 days.

SUMMARY AND CONCLUSION

The effect of gamma radiation on the growth of corn plantlings was determined and it is expected that if the dosage of gamma radiation which the plants are exposed is increased, then there would be greater inhibition in the growth of the plant.

20 corn seeds served as control and were not exposed to radiation while 20 corn seeds were irradiated with 10 krad of radiation while another 20 with 30 krad and 20 more exposed to 50 krad. These seeds were planted and observed from October 15 to December 1 and the heights of the plants were measured and recorded.

Results showed that the seeds exposed to 10 krad grew more rapidly and taller than any of the other seeds— growing up to an average of 89 cm— and the seeds in the control group had the second tallest average height of 80.88 cm. Seeds exposed to the 30 krad group reached the third highest average height (8.20 cm) and the lowest average height was 3.50 cm which was observed with the seeds that were exposed to 50 krad of radiation. Kim, et al. (2004) suggests that there is a stimulation of the adjustment of the production of chlorophyll in the plant which could have indirectly caused enhancement of plant growth.

Even though the highest average height was attained by plants exposed to 10 krad of radiation, the greatest percent germination (50%) was obtained by the seeds in the control group followed by 25% from the seeds exposed to 10 krad radiation, then 15% germination from both groups exposed to 30 and 50 krad.

The highest percent survival (60%) was also achieved by seeds in the control group and the next highest was found in the seeds exposed to 10 krad of 20% survival. The groups of seeds exposed to 30 and 50 krad of gamma radiation both had no survivors by the end of the observation period but the corn plants irradiated with 30 krad lasted about 14 days longer than the ones exposed to 50 krad of radiation.

These results were observed because high doses of radiation caused damaging effects on the sugar phosphate backbone of the DNA and that could have caused mutations that harmed the corn plant that developed from the seed (Ram, 2010).

Therefore the application of gamma radiation does not immediately cause inhibition of plant growth with increasing levels. Low doses of radiation could actually improve plant growth compared to no radiation at all but high doses already cause inhibition of growth and lethal mutations for the plant.

LITERATURE CITED

Fire, F. 2009.The common sense approach to hazardous materials. 3rd ed. Tulsa, OK:

Fire Engineering. p. 343.

Kim, J. H., Baek, M. H., Chung, B. Y., Wi, S. G., and Kim, J. S.. 2004. Alterations in the

photosynthetic pigments and antioxidant machineries of red pepper (Capsicum

annuum L.) seedlings from gamma-irradiated seeds.Journal of Plant Biology.

doi:10.1007/BF03030546.

Ram, M. 2010.Fundamentals of cytogenetics and genetics. New Delhi: PHI Learning

Private Limited. p. 328.

Ramirez, D., Mendioro, M., & Laude, R. 2013.Lectures in genetics. 10th ed. Los Banos:

Genetics and Molecular Biology Division. pp. 163-175.

Somogyi, L., Ramaswamy, H., & Hui, Y. 1996.Processing fruits: Science and

technology.Vol. 1. Boca Raton, FL: CRC Press. pp. 224-225.

Wang, W., Gorsuch, J., & Hughes, J. (eds.). 1997.Plants for environmental studies.

Boca Raton, FL: CRC Press. p. 51.

APPENDIX

Table 1. Height of corn plants exposed to different doses of gamma radiation.

DATE

0 krad

10 krad

30 krad

50 krad

No. of plants observed

Average height (cm)

No. of plants observed

Average height (cm)

No. of plants observed

Average height (cm)

No. of plants observed

Average height (cm)

October 15

9

9.41

5

10.10

3

6.97

3

2.17

October 17

10

12.50

4

18.00

3

7.67

3

3.50

October 20

9

18.83

4

23.00

2

5.75

0

0.00

October 22

8

22.81

4

29.18

1

6.00

0

0.00

October 24

8

23.21

4

30.03

1

8.20

0

0.00

October 27

8

24.65

4

34.43

1

8.00

0

0.00

October 29

8

26.06

4

37.00

1

7.00

0

0.00

October 31

8

26.93

4

37.63

1

6.50

0

0.00

November 3

8

30.40

4

42.23

0

0.00

0

0.00

November 5

8

31.41

4

44.03

0

0.00

0

0.00

November 7

8

33.93

4

45.63

0

0.00

0

0.00

November 10

8

39.47

3

55.50

0

0.00

0

0.00

November 12

8

43.38

2

67.50

0

0.00

0

0.00

November 14

6

53.83

2

66.00

0

0.00

0

0.00

November 17

6

59.67

2

65.25

0

0.00

0

0.00

November 19

6

65.58

2

68.50

0

0.00

0

0.00

November 21

6

66.50

2

69.75

0

0.00

0

0.00

November 24

6

73.67

1

80.00

0

0.00

0

0.00

November 26

6

78.17

1

87.00

0

0.00

0

0.00

November 28

6

75.17

1

 

0

0.00

0

0.00

December 1

6

80.88

1

89.00

0

0.00

0

0.00

                 

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