Arts, M.T., H. Rai
Abstract:
We used a Phototron to provide a controlled environment to measure the effects of different doses of UV-B radiation on carbon allocation to macromolecular end-products of photosynthesis. In Nitzschia palea and Cryptomonas sp. derived from chemostats, carbon allocation was non-systematically affected by exposure to UV-B radiation. The effects of UV-B on these two species were non-stochastic with a definite threshold that depended on the species and on the visible light climate. Even relatively short, ca. 5 min, exposures to intermediate to high doses of UV-B (0.070 to 0.448 mW@cm^-2) had a negative effect on the gross rate of photosynthesis. Brief (<60 min.) exposures to low doses of UV-B (0.020 mW@cm^-2) had a stimulatory effect on lipid and polysaccharide production in N. palea and Cryptomonas sp., respectively. Protein to low molecular weight ratios provided the best general stress response descriptor. The fraction of carbon incorporated to lipids generally increased as a function of increased UV-B dose except in the case of very low exposure doses in N. palea where the opposite was found. These experiments demonstrate that the allocation of carbon to recently produced photosynthates under the influence of UV-B radiation is likely to be species-specific and will also depend on the UV-B dose and on the underwater light climate (PAR).
(National Hydrology Research Institute, 11 Innovation Blvd., Saskatoon, Saskatchewan, Canada S7N 3H5)
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