Poster: Photomorphogenesis

Abs # 516: Distinctive features of UV-absorbing pigment accumulation in response to short-wavelength UV-B

Presenter:	Shinkle, James R, jshinkle@trinity.edu
Authors	Shinkle, James R (A)   Shaltz, Abby  (A)   Barnes, Paul W (B)
Affiliations:	(A): Trinity University (B): Southwest Texas State University, San Marcos

Although incident solar radiation does not contain significant ultraviolet (UV) radiation at wavelengths < 290 nm, plants show adaptive responses to short wavelength UV-B (290-300 nm) and UV-C (220-290 nm) light. We have identified features of UV-induced accumulation of UV absorbing pigments specific to exposure to short wavelength UV-B or UV-C light. Cucumber seedlings were grown in dim red light to maintain an etiolated growth form. At five days plants were irradiated with short (1-100 min) pulses of UV light. Full spectrum UV-B (FS-UVB, 290-320 nm) light was provided from a transilluminator. Cellulose acetate was used to filter out wavelengths shorter than 300 nm, leaving long wavelength UV-B (LW-UVB). Light intensity at plant level was 898 and 827 mW m^-2 for FS-UVB and LW-UVB respectively. At designated times after irradiation, the first cm of the hypocotyls was excised and extracted in methanol/1% HCl for 48 h at –20^o C. Absorbance was read at 317 nm or from 250-400 nm. We found that the threshold for induction of accumulation of UV absorbing pigments was at 3 min exposure (0.16 kJ m^-2) for FS-UVB, while 30 min (1.5 kJ m^-2) exposure to LW-UVB was required to induce an increase in UV absorbance. The time courses for the two responses differed as well. Scans of extracts taken at 12h after irradiation showed that LW-UVB caused an increase in the magnitude of absorption relative to unirradiated controls, but the shape of the curve was unchanged. FS-UVB induced a new peak in the absorption spectrum at 260-270 nm. Plants irradiated with UV-C (germicidal lamp, peak output at 256 nm) showed the same change in absorbance spectrum as FS-UVB treated plants. A hypothesis that DNA damage is the sensory mechanism for the response to short wavelength UV will be presented.