Poster: Photosynthesis

Abs # 370: UV-A synergistically interacts with UV-B in cellulose acetate filtered radiation: photosynthetic effects

Presenter:	Jahnke, Lee S, lsj@christa.unh.edu
Authors	Jahnke, Lee S (A)   White, Andrea L (A)
Affiliations:	(A): Department of Plant Biology, University Of New Hampshire

Standard ‘UV-B’ fluorescent lamps emit approximately equal fluxes of UV-A and UV-B along with some UV-C. The long established procedure uses Cellulose Acetate (CA) to remove UV-C, allowing the transmission of both UV-A and B. Subsequently the B portion is removed with a Mylar type of filter. It is assumed that physiological responses observed with CA filtered radiation that disappear with Mylar filtered radiation must be caused simply by the UV-B and not by the UV-A. We compared this procedure with a new radiation filter (solution of alkaline K₂CrO₄) that removes UV-C and UV-A while transmitting only the UV-B portion of the short-wavelength spectrum. Equal UV-B fluxes filtered either by CA or chromate were compared in 24h exposures of cultures of Dunaliella tertiolecta. Exposure to 5 µmol m^-2 s^-1 UV-B filtered by CA produced decreases of 55% in Fv/Fm ratios and 50% reduction in light-saturated photosynthetic rates. With the Mylar ‘control’ (transmitting only UVA), no inhibition was observed. When 5 µmol m^-2 s^-1 UV-B free of UV-A (filtered by alkaline chromate solution) was used, no inhibition of Fv/Fm ratios nor inhibition of light-saturated photosynthesis were observed.