Regulation of enzymes involved in C4 photosynthesis and the antioxidant metabolism by UV-B radiation in Egeria densa,a submersed aquatic species |
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Authors: | Casati Paula Lara María V Andreo Carlos S |
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Institution: | (1) Centro de Estudios Fotosintéticos y Bioquímicos (CEFOBI), Universidad Nacional de Rosario, Suipacha 531, Rosario, 2000, Argentina |
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Abstract: | Egeria densa, a submersed aquatic species, was exposed to different treatments under UV-B radiation, and the response 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 with an increase in the activity of some isoforms of several enzymes involved
in the antioxidant metabolism, such as superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT) and peroxidase
(POD). The content of chlorophylls and carotenoids was considerably decreased, suggesting that degradation or repression of
the synthesis of these molecules may be occurring after UV-B exposure. Reactive oxygen species (ROS) were also required for
UV-B induction of PEPC and NADP-ME, as the addition of ascorbic acid before UV-B treatment prevented the induction of these
enzymes, while salicylic acid was not effective in inducing NADP-ME but increased the expression of the lower molecular mass
isoform of PEPC. On the other hand, damage to the photosynthetic machinery may be occurring after exposure to UV-B radiation
for 8 per day over 1–2 days, as indicated by a decrease in the levels of Rubisco, PEPC and NADP-ME. Some of the enzymes involved
in the antioxidant metabolism, such as CAT 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 on the UV-B treatment.
This revised version was published online in June 2006 with corrections to the Cover Date. |
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Keywords: | antioxidant enzymes ascorbic acid Egeria densa NADP-malic enzyme phosphoenolpyruvate carboxylase reactive oxygen species Rubisco salicylic acid UV-B |
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