gamma radiation

Gamma Radiation and its Effect on Corn (Zea mays) Physiology, Morphology, and Cytology

Sharmaine Joy L. Espinola, Xadrix D. Yanzon Bicol University, College of Science, Department of Biology, Legazpi City, Albay

Abstract Inducing gamma radiation is investigated to cause aberrations in plants. The study was conducted to determine the effects of gamma radiation on corn morphological development and cytology. Corn seeds were irradiated with varying dosage of 40, 50 and 80 peak kilovolts (kvp) with a constant time exposure of .20 seconds. A separate set up was prepared for observing the cells with aberrations. Results are observed by studying the seed germination, growth, development, and biochemical characteristics of maize. Treatment of corn seeds with gamma radiation showed increasing patterns in terms of final percent germination and plant height for doses up to 50 kvp but gradual decrease was observed in 80 kvp. Seeds that are treated with gamma radiation of 0-50 kvp have optimum development while the highest dose of 80 kvp has also high development rate but doesn’t reach the highest growth rate comparable to the mid-treatment. Increasing irradiation dose doesn’t always make aberration more visible. Inverted U curve is observable in the highest dose treatment, while the mid-treatment results having an optimum treatment that has varying results. Statistical analysis is used, resulting that at least one of the treatment varies and rejecting the idea that this experiment is a null test or the different treatment has a very close findings. The study shows that gamma radiation has no growth inhibiting effect but has increasing growth rate effect comparable to the control. Keywords: Gamma radiation, aberration, corn, final percent germination, stimulate Keywords:Introduction Gamma radiation, aberration,

Mutation, as defined by Hartl (2011) is a heritable alteration in a gene or chromosome. It occurs when the genetic message carried by the gene has been altered or damaged (Mendioro et al., 2010). Mutation can be classified according to its origin whether it is spontaneous or induced. If a mutation occurs in the absence of a mutagen then it is spontaneous. On the other hand, mutations that occur in the presence of a mutagen is called induced. A mutagen is an agent that is capable of increasing the rate of mutation. Different chemicals and radiation may act as a mutagen. Ionizing radiation such as x-rays or gamma radiation is a potent mutagen (Hartl 2011). Ionizing radiation has paved its way in revolutionizing modern day researches in

the field of agriculture and food technology. Gamma radiation, as stated by Marcu et.al (2012) has been proved to be economical and efficient as compared to other ionizing rays and also because of its penetrating power. This penetrating power helps in the wider scope of application in the enhancement of different plant species (Moussa 2006). The biological effect of gamma rays is based on the interaction with atoms or molecules in the cell, particularly water to produce free radicals (Kova’cs and Keresztes 2002). This can cause damage in the different components due to the said interaction (Esnault et al. 2010). Studies concerning the effects of gamma radiation in plants have been carried out using different indicators in plant responses. Morphological and

physiological developments served as the measurable reaction to different radiation doses. Several researchers reported that low doses of gamma radiation stimulated the growth of plants such as rice (Oryza sativa) (Maity et al. 2005). Marcu, D. et al. (2012) reported that irradiation dose between 2-30 Gy enhanced the growth parameters such as final percent germination and shoot length as compared to untreated plants. Also, seeds treated with 70 Gy showed drastic reduction in length of shoots. The purpose of this study were to compare the effects of corn (Zea mays) irradiation with gamma radiation at different doses in terms of different parameters such as final percent germination, shoot length and cytology. The result of this study could be used to improve different plant breeding programs and to also improve the traits of the plant that is beneficial in agriculture.

Methodology Obtaining of seeds and irradiation The corn (Zea mays) seedlings was procured from the market. Two hundred corn (Zea mays) was taped in a cardboard or a folder. There were three treatments and a control. Each of the treatment has fifty seeds each and taped at different cardboards with labels. The corn (Zea mays) seedlings were irradiated at Sacred Heart Clinic at Legazpi City, Albay. Treatment 1 (T1) was irradiated at 40 kvp, treatment 2 (T2) at 50 kvp and treatment 3 (T3) at 80 kvp with a constant time exposure of .20 seconds.

Planting of seeds The corn (Zea mays) seedlings were planted at a plastic container with the same size and same thickness and brand of tissue paper. The water was also controlled. Two set-ups were made with three replicates for each treatment. Each replicate has five seedlings each. The set-ups were placed near a window and it has been arranged randomly every other day to avoid bias. The measurement was conducted every twenty-four hours. Plant height was measured and the percent germination. Chromosomal Aberration Set-up

After two to three days of growing the chromosomal aberration set-up, the roots were cut and placed in a farmer’s fluid to preserve the tips. To prepare the slides, place the root tip in a glass slide then add 10 N HCl to dissolve the middle lamellae and soften the cells for 15 minutes. When the root tip becomes almost transparent and soft when touched with a dissecting needle, crush the tip then add a drop of giemsa stain on a clean slide for twenty minutes and lay a clean coverslip. Place the coverslip carefully to avoid some bubbles. Apply heat on the slide in the alcohol lamp. Apply pressure over the cover slip with your thumb to flatten and disperse the cells. Final Germination Percentage Percent germination was recorded every day. The emergence of the roots was used as the index of germination. The germination percentage was calculated using the following formula: (FGP)= (Number of seeds germinated after n days/ Total number of seeds) x one hundred (100)

Statistical Analysis Experimental data were subjected to a one-way analysis of variance (oneway ANOVA) to determine if there is any significant differences between the means of the treatments. Results

Table 2 shows the graph for the average plant height tabulated in table 1. T0 to T2 showed and increasing height while there is gradual decrease in T3.

Table 3

Table 1 PERCENT GERMINATION TREATMENT R1 R2 R3 R1 R2 R3 R1 R2 R3 R1 R2 R3

T0

T1

T2

T3

AVERAGE HEIGHT 11.68 12.16 22.98 17.4 13.3 27.2 24.94 20.58 23.74 17.78 20.64 19.42

15.61

19.29 23.09 19.28

Table 1 shows the average height per replicate and average height per treatment. Table 2. 25.00

100 90 80 70 60 50 40 30 20 10 0

T0 1

T1 2

T2 3

T3

4

Percent germination of each treatment is being showed in table 3. Treatment 2 has the highest percent germination having 100 percent germinated seeds while the control and treatment three has the lowest percent germination with only 80 percent of the seeds germinated.

Average Plant Height Figure 1.

20.00 15.00

SUMMARY

10.00

Groups T0 T1 T2 T3

5.00 0.00 1T0

T1 2

3T2

4T3

Count Sum Average Variance 15 234 15.6 160.07 15 289 19.3 265.17 15 346 23.1 134.46 15 289 19.3 307.11

Figure 1 shows that summary of the data statistics used. Showing that treatment 2 has the highest average height but has the lowest variance between individuals on the same treatment. Figure 2

ANOVA Source of Variation

SS

between groups

419.69

within groups

12135

56 217

Total

12555

59

DF

MS

F

Pvalue

Fcritical

3 140 0.6456 0.589 2.7694

Figure 2 shows the analysis of variance test final table. Showing the summation square, degrees of freedom, mean square, F value, P- value between groups (among the treatments) and within groups (in the treatment). It also shows that F value is greater than the Pvalue and not exceeding the F critical value. F > Pvalue < Fcritical. Clearly showing that the problem is not a null test and has at least one treatment is showing variance comparable to the other treatments, and has an acceptable result due to the resulting F value is not exceeding to the critical value given by the data.

Treatment of corn seeds with gamma radiation showed increasing patterns in terms of final percent germination and plant height for doses up to 50 kvp. The results shows the hormetic effect obtained from previous studies conducted. Seeds that are treated with gamma radiation of 0-50 kvp have optimum development while the highest dose of 80 kvp has also high development rate but doesn’t reach the highest growth rate comparable to the mid-treatment. Irradiation of seeds greatly affected the cells obtained from the tips. Anaphase bridges as shown in Figure 3e are the most common found in all treatments with radiation. They can also be easily distinguished as compared to other aberrations. A multinucleate aberration in Figure 3f was found at treatment 3. In treatment 1 and 2, one of the most common aberration is the fragments in prophase in Figure 3j. Disturbed prophase illustrated in Figure 3i was found in treatment 2. The remaining aberrations (Figure 3g, k, and l) are found in treatment 3 with a higher dose of radiation.

a.

b.

c.

e. d.

e.

f.

g.

h.

i.

k.

j.

l.

Fig. 3. Mitotic cells derived from corn (Zea mays) root tips. Normal cells from tips without radiation. These include a. Prophase, b. and g. Metaphase, c. Anaphase, d. Telophase. Cells from irradiated tips include some aberration, e. anaphase with a chromosome bridge, f. multinucleate, h. disturbed prophase i. anaphase with bridge, j. fragments k. Anaphase with bridge and l. fragment chromosome at metaphase.

Discussion The results of the effects of irradiation based on the comparison of final germination percentage and plant growth (plant height) content of irradiated and non-irradiated emphasizes the stimulatory effects of low doses (40 kvp50 kvp) and the inhibitory effect of a high dose. This phenomenon is called hormesis effect. It is a term used by toxicologists to refer to a biphasic dose response to an environmental agent characterized by a low dose stimulation beneficial effect and a high dose inhibitory result (Mattson, 2008). Low dose is defined as any dose between ambient levels of radiation and the point that arcs the boundary between biopositive and bionegative (Luckey, 2003). The reaction varies on plant morphology and physiology, species age, genome size and composition,

dose, time of exposure, type of radiation and etc (Marcu et al, 2013). The stimulatory effects induced by gamma radiation on germination might be the acceleration of cell division as stated by Zaka et al. (2004) or it might be attributed to the ribonucleic acid or protein synthesis activation (Abdel-Hady et al. 2008). Low doses of radiation may increase the enzymatic activation and the awakening of the young embryo, which results in stimulating the rate of cell division and enhances not only the germination but also the growth and flowering capacity (Sjodin, 1962). In the results, the treatment with the highest dose of 80 kvp did not show any inhibitory effect but it did show some decrease in plant height and germination as to compare to the mid-treatment. Plants irradiated with high doses of radiation disturbs synthesis of protein, hormone balance, leaf-gas exchange, water exchange and enzyme activity that leads to plant physiology and morphology disorders and inhibition of

plant growth and development (Hameed et al. 2008).

that helped and guided us in preparing the slides.

During normal mitotic cycle in cells without radiation, chromosomes do not have any breakage or rearrangements. After irradiation, strands of chromosomes can break at various points along their lengths. Such changes are called chromosomal aberration. With an increasing radiation dose, the extent of chromosome breakage increases. This interaction of chromosomal breakage and mitosis produces nuclear imbalance (Schwartz and Bay, 1956). Most aberration are easily found in metaphase and anaphase. Such as the chromosome bridge that results from two centromeres moving to opposite poles in anaphase then the material is stretched in between across the cytoplasm.

References:

Chromosome breakage and rearrangements lead to cell lethality only when they are followed by mitosis. This might cause the inhibitory effect in plants exposed in radiation. Recommendations Future studies that will be conducted should fairly emphasize the varying dosage of radiation and longer time exposure of the seeds to differ results obtained.

Acknowledgement The researchers would like to express their most sincere gratitude to Mrs. Shirley Armenta for irradiating the corn seeds without doubt and in exchange of nothing. Also to some of our classmates

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