Regulation of enzymes involved in C4 photosynthesis and the antioxidant metabolism by UV-B radiation in Egeria densa, a Submersed Aquatic Species

CASATI, PAULA; LARA, MARIA V.; ANDREO, CARLOS S.

PHOTOSYNTHESIS RESEARCH

SPRINGER

Año: 2002 vol. 71 p. 251 - 264

0166-8595

Egeria densa, a submersed aquatic species, was exposed to different treatments under UV-B radiation, and theresponse of phosphoenolpyruvate carboxylase (PEPC) and NADP-malic enzyme (NADP-ME) was determined.Exposure to UV-B radiation for 4 h per day over 7?16 days caused an increase in both enzymes, together withan increase in the activity of some isoforms of several enzymes involved in the antioxidant metabolism, such assuperoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT) and peroxidase (POD). The content ofchlorophylls and carotenoidswas considerably decreased, suggesting that degradation or repression of the synthesisof these molecules may be occurring after UV-B exposure. Reactive oxygen species (ROS) were also required forUV-B induction of PEPC and NADP-ME, as the addition of ascorbic acid before UV-B treatment prevented theinduction of these enzymes, while salicylic acid was not effective in inducing NADP-ME but increased the expressionof the lower molecular mass isoform of PEPC. On the other hand, damage to the photosynthetic machinerymay be occurring after exposure to UV-B radiation for 8 per day over 1?2 days, as indicated by a decrease in thelevels of Rubisco, PEPC and NADP-ME. Some of the enzymes involved in the antioxidant metabolism, such asCAT and APX, were also sensitive to continuous exposure, evidenced by a decrease in their activity. In this way,in E. densa, several enzymes involved in different metabolic pathways showed a distinct response, depending onthe UV-B treatment.