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Structural and metabolic changes in rhizophores of the Cerrado species Chrysolaena obovata (Less.) Dematt. as influenced by drought and re-watering.

Abstract

Chrysolaena obovata stores inulin in the rhizophores, associated with drought tolerance. Few studies reported the interactive effects of high [CO2] and drought in native species. Here we evaluated the combined effects of these factors on water status and fructan metabolism. Two lots of plants were kept at 380 and 760ppm [CO2] in open-top chambers. In each [CO2] plants were divided in four groups grown under different water availability: watered with 100 (Control), 75 (low), 50 (medium) and 25% (severe drought) of the water evapotranspirated in the last 48 h. In each water treatment plants were collected at 0, 9, 18 and 27 d. On day 27, all plants were re-watered to field capacity and, after 5 days, a new sampling was made. Water restriction caused a decrease in plant moisture and in photosynthesis, especially in 25% plants in both [CO2]. Fructosyltransferases and fructan-hydrolase activities were generally lower in water restricted plants, regardless of the [CO2]. Re-watering caused a more pronounced increase in hydrolase activity in water restriction under 760 than under 380ppm. Changes in fructan contents were not clearly detected as differences in fructan composition. Under 380ppm at 25%, a 6 fold increase was observed in the proportion of hexoses, in relation to oligosaccharides (FOS), especially at 27 days, while under 760ppm, a two fold increase was observed. After re-watering, FOS and hexoses increased in 25% plants under both [CO2]. Results obtained with 25% plants in both [CO2] were similar to the reported previously for C. obovata under drought, i.e. increase in hexose content, modification of fructan chain size and maintenance of water status. Under 50 and 75%, plants seemed to have acclimated to water restriction, however more efficiently under high [CO2], due to adjustments in fructan metabolism, maintaining similarities with unrestricted plants. Our results also suggest that elevated [CO2] may enhance drought tolerance weakening the effect of water restriction on fructan metabolism. (AU)

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