Living in transparent lakes: Low food P:C ratio decreases antioxidant response to ultraviolet radiation in Daphnia.

BALSEIRO ESTEBAN; SOUZA MARÍA SOL; MODENUTTI BEATRIZ; REISSIG MARIANA

LIMNOLOGY AND OCEANOGRAPHY

The American Society of Limnology and Oceanography

Año: 2008 vol. 53 p. 2383 - 2390

0024-3590

We experimentally tested the effect of food quality (P:C ratio) on the response ofantioxidant enzymes to ultraviolet radiation (UVR) in Daphnia commutata fed withChlamydomonas reinhardtii. Algal cultures were grown at different concentrations ofphosphorus and light intensities, resulting in significant differences in the P:C ratios(μmol P•[mmol C]-1) (6.05, 1.70, and 0.83). After 12 days of D. commutata growthunder these three food quality treatments, we observed significant differences inDaphnia individual biomass and protein content. Subsequently, we carried out anultraviolet exposure experiment to determine if stoichiometric constraints imposedwould limit enzymatic defenses against UVR oxidative stress. The UVR exposureexperiment consisted of a factorial design with three levels of food P:C (low, mediumand, high) and two levels of UVR (exposed and protected). The activities of GlutathioneS-Transferases (GST) and Catalase (CAT), enzymes involved in protection and repair ofdamage caused by UVR, were determined. Enzyme activities in the animals exposed toor protected from UVR showed a direct relationship with food P:C ratio that fitexponential models. Although GST and CAT differed slightly in their response to UVR,both enzymes were significantly affected by food quality: in low P:C treatments, therewas a significant lower enzyme activity in response to UVR for both enzymes. A lowfood quality (less P for biosynthesis) may also impose a weaker antioxidant response ofthe organisms, a response of considerable ecological relevance in transparent Andeanlakes which combine high UVR intensities with low seston P:C ratios.