Antioxidant response of soybean cotyledons (Glycine max) to ultraviolet irradiation

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Abstract
After 24 h of UV-B + UV-C irradiation the homogenates of superficial layers of soybean cotyledons (Glycine max var. Hood) contained significantly more tocopherol (133%) and ascorbic acid (20%) than the control. However, UV-B irradiation alone did not affect the content of these antioxidants. Neither β-carotene nor thiol content was significantly affected after UV-B or UV-B + UV-C irradiation. Pigmentation of cotyledons from control and UV-B-exposed plants did not differ visibly, but cotyledons from plants exposed to UV-B + UV-C accumulated a red pigment in the epidermis 15 h after receiving the UV radiation. Spectral analysis indicated a substantial increase in absorbance between 250 and 340 nm after UV-B + UV-C exposure, compared with controls. Ethanolic extracts from UV-B + UV-C-irradiated cotyledons showed a significant peak at 532 nm at pH 10, which was not seen at pH 6. Successive changes in pH were accompanied by reversible changes in the spectra. TLC studies indicated that Rf values for the pigment were 0.75 and 0.63 in Forestal and formic solvents, respectively. By comparison with literature values, these results are consistent with the features of apigeninidin. The results suggest that UV-B irradiation and UV-C irradiation affect different mechanisms at the cellular level. Key words: Antioxidants, colored pigment induction, cotyledon, ultraviolet irradiation, UV-B + UV-C

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