Abstract
Chrysolaena obovata (Less.) Dematt., previously named Vernonia herbacea, is an Asteraceae native to the Cerrado which accumulates about 80% of the rhizophore dry mass as inulin-type fructans. Considering its high inulin production and the wide application of fructans, a protocol for C. obovata in vitro culture was recently established. Carbohydrates are essential for in vitro growth and development of plants and can also act as signaling molecules involved in cellular adjustments and metabolic regulation. This work aimed to evaluate the effect of different sources of carbohydrate on fructan metabolism in plants grown in vitro. For this purpose, C. obovata plants cultivated in vitro were submitted to carbon deprivation and transferred to MS medium supplemented with sucrose, glucose or fructose. Following, their fructan composition and activity and expression of genes encoding enzymes for fructan synthesis (1-SST and 1-FFT) and degradation (1-FEH) were evaluated. For qRT-PCR analysis partial cDNA sequences corresponding to two different C. obovata genes, 1-SST and 1-FFT, were isolated. As expected, C. obovata sequences showed highest sequence identity to other Asteraceae 1-SST and 1-FFT, than to Poaceae related proteins. A carbon deficit treatment stimulated the transcription of the gene 1-FEH and inhibited 1-SST and 1-FFT and carbohydrate supplementation promoted reversal of the expression profile of these genes. With the exception of 1-FFT, a positive correlation between enzyme activity and gene expression was observed. The overall results indicate that sucrose, fructose and glucose act similarly on fructan metabolism and that 1-FEH and 1-SST are transcriptionally regulated by sugar in this species. Cultivation of plants in increasing sucrose concentrations stimulated synthesis and inhibited fructan mobilization, and induced a distinct pattern of enzyme activity for 1-SST and 1-FFT, indicating the existence of a mechanism for differential regulation between them.
Highlights
The Cerrado and its savanna like vegetation is the second largest biome in the Brazilian territory, being outsized only by the Amazon rain forest
As tissue culture is considered a valuable tool for the study of primary and secondary metabolisms, in this paper we report the use of this technique to evaluate the effect of different carbon sources on the modulation of the activity and expression of enzymes involved in fructan synthesis and mobilization in plants of C. obovata cultivated in vitro
To further evaluate the relative expression of all fructan metabolism genes in response to different carbon sources, and since no genomic information is available for C. obovata, partial 1-SST and 1-FFT cDNA
Summary
The Cerrado and its savanna like vegetation is the second largest biome in the Brazilian territory, being outsized only by the Amazon rain forest. It covers approximately 21% of the Brazilian land area and is characterized by a well-defined seasonality, concerning the water regime, which includes a humid summer and a dry winter often lasting up to 5 months (Eiten, 1972; Coutinho, 2002). Previous results showing efficient production of inulin in field trials and in vitro by C. obovata (Carvalho et al, 1998; Trevisan et al, 2014) suggest that this native species could be a promising alternative for fructan production, since inulin for commercial use is mainly extracted from roots of Chichorium intybus L
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