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

After 24 h of UV-B + UV-C irradiation the homogenates of superficial layers of soybean cotyledons (Glycine mar 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 beta-carotene nor thiol content was significantly affected after UV-B or U V-B + UV-C irradiation. Pigmentation of cotyledons from control and UV-B-ex posed 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 ab sorbance between 250 and 340 nm after UV-B + UV-C exposure, compared with c ontrols. 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. Successiv e changes in pH were accompanied by reversible changes in the spectra. TLC studies indicated that R-f values for the pigment were 0.75 and 0.63 in For estal and formic solvents, respectively. By comparison with literature valu es, these results are consistent with the features of apigeninidin. The res ults suggest that UV-B irradiation and UV-C irradiation affect different me chanisms at the cellular level.