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International Journal of Botany

Year: 2007 | Volume: 3 | Issue: 1 | Page No.: 109-113
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Authors

Nadia H. Noaman

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Research Article

Ultraviolet-B Irradiation Alters Amino Acids, Proteins, Fatty Acids Contents and Enzyme Activities of Synechococcus leopoliensis

Nadia H. Noaman
In a previous study, four mutants (M1, M2, M3 and M4) were isolated by exposure of Synechococcus leopoliensis to ultraviolet-B irradiation for 5, 10, 15 and 20 min, respectively. Analyses were performed to make a comparison to the effect of UV on the contents of amino acids, proteins, fatty acids and some enzyme activities of the parent type and mutants. The study shows that total proteins and some amino acids in S. leopoliensis as lysine and arginine decreased by the exposure to UV irradiation, while aspartic increased. Cysteine, alanine and valine completely disappeared from M1, M2 and M3, respectively, while proline disappeared from M1 and M4. A drop in the contents of the aromatic amino acids, phenylalanine and tyrosine occurred in the four mutants. S. leopoliensis showed the disappearance of four fatty acids by the exposure to UV for 10 min, While C17: 1, C 8: 0 and C 15: 0 disappeared from M1, M3 and M4, respectively. C14: 0, which was absent at the parent type, appeared at all the mutants and it was found to increase with increasing the exposure time. All fatty acids of S. leopoliensis, which were present at the parent type, decreased after exposure to UV for 5 min except C15: 0. 10 min and above caused all the fatty acids to decrease with increasing the exposure time except C6: 0, C10: 0, C11: 0, C14: 0, C15: 0 and C18: 3. There was a drop in C18:3 in S. leopoliensis by its exposure to UV for 5 min, which was followed by the increase of that fatty acid with increasing the exposure time. Total saturated, mono, polyunsaturated fatty acids and proteins showed a decrease by increasing the exposure to UV. Enzymes namely μ-esterase, peroxidase and glutamate dehydrogenase were studied for S. leopoliensis and the four mutants. Five minutes exposure to UV increased the activity of peroxidase and glutamate dehydrogenase, but lowered the activity of α-esterase by 93%. More than 5 min exposure to UV caused glutamate dehydrogenase activity to decrease with increasing the exposure time, while peroxidase activity increased. The results of decreased UV-absorbers amino acids in the four mutants suggests that the mutants have a defect in the ability to synthesize them to protect the mutants against the damaging affect of UV radiation. The findings also suggests that the increase of exposure to UV-B irradiance not only affect the contents of amino acids, fatty acids and proteins but also alters enzyme activities in S. leopoliensis.
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