RESUMO
The main goal of this study was to generate potato tubers with increased levels of flavonoids and thus modified antioxidant capacities. To accomplish this, the vector carrying multigene construct was prepared and several transgenic plants were generated, all overexpressing key biosynthesis pathway enzymes. The single-gene overexpression or simultaneous expression of genes encoding chalcone synthase (CHS), chalcone isomerase (CHI), and dihydroflavonol reductase (DFR) resulted in a significant increase of measured phenolic acids and anthocyanins. The increase in phenolic compounds synthesis is accompanied by decreases in starch and glucose levels in transgenic plants. The flavonoids-enriched plants showed improved antioxidant capacity; however, there is a complex relationship between antioxidant capacity and flavonoids content, suggesting the great participation of other compounds in the antioxidant potential of the plants. These other compounds are not yet recognized.
Assuntos
Antioxidantes/análise , Fenóis/análise , Plantas Geneticamente Modificadas , Solanum tuberosum/química , Solanum tuberosum/genética , Aciltransferases/genética , Oxirredutases do Álcool/genética , Antocianinas/análise , Ácidos Cafeicos/análise , Ácido Clorogênico/análise , Liases Intramoleculares/genética , Solanum tuberosum/enzimologiaRESUMO
Transgenic potato plants overexpressing and repressing enzymes of flavonoids biosynthesis were created and analyzed. The selected plants clearly showed the expected changes in anthocyanins synthesis level. Overexpression of a DNA encoding dihydroflavonol 4-reductase (DFR) in sense orientation resulted in an increase in tuber anthocyanins, a 4-fold increase in petunidin and pelargonidin derivatives. A significant decrease in anthocyanin level was observed when the plant was transformed with a corresponding antisense construct. The transformation of potato plants was also accompanied by significant changes in steroid alkaloid glycosides (SAG) level in transgenic potato tuber. The changes in SAGs content was not dependent on flavonoid composition in transgenic potato. However, in an extreme situation where the highest (DFR11) or the lowest (DFRa3) anthocyanin level was detected the positive correlation with steroid alkaloid content was clearly visible. It is suggested that the changes in SAGs content resulted from chromatin stressed upon transformation. A liquid chromatography/mass spectrometry (LC/MS) system with electrospray ionization was applied for profiling qualitative and quantitative changes of steroid alkaloid glycosides in tubers of twelve lines of transgenic potato plants. Except alpha-chaconine and alpha-solanine, in the extracts from dried tuber skin alpha-solamargine and alpha-solasonine, triglycosides of solasonine, were identified in minor amounts, triglycosides of solanidine dehydrodimers were also recognized.
Assuntos
Alcaloides/análise , Antocianinas/análise , Glicosídeos/análise , Solanum tuberosum/química , Solanum tuberosum/metabolismo , Esteroides/análise , Oxirredutases do Álcool/genética , Oxirredutases do Álcool/metabolismo , Cromatografia Líquida de Alta Pressão , Estrutura Molecular , Epiderme Vegetal/química , Raízes de Plantas/química , Plantas Geneticamente Modificadas , Solanum tuberosum/genética , Espectrometria de Massas por Ionização por ElectrosprayRESUMO
Recently, transgenic potato plants were created showing underexpression of the 20R isoform of the 14-3-3 protein. The transgenic plants grown in tissue culture showed a significant increase in nitrate reductase activity and a decrease in nitrate level. The transgenic line with the lowest 14-3-3 quantity was field-trialed (1997-2000) and analyzed. The reduction in the 14-3-3 protein level consistently resulted in a starch content increase and in an increase in the ratio of soluble sugars to starch in the tubers, although the latter was only barely visible. The determination of amino acid composition in the tubers showed a significant increase in methionine, proline, and arginine content and a slight but consistent increase in hydrophobic amino acid and lysine content in the cells of the transgenic potato plants. We also observed an increase in the crude protein content, from 19 to 22.1% of the control value in consecutive years. It is proposed that all of these changes might have resulted from the downregulation of nitrate reductase and sucrose phosphate synthase activities by 14-3-3, although other potential mechanisms cannot be excluded (e.g., an increase in enzyme protein level). 14-3-3-repressed transgenic plants showed a significant increase in calcium content in their tubers. It is thus proposed that a function of the isolated 14-3-3 isoform is in the control of amino acid synthesis and calcium metabolism. However, the mechanism of this control is as yet unknown.
