Estudos da biossíntese das piranocumarinas xantiletina e seselina em laranja pêra (Citrus sinensis (L.) Osbeck) e limão cravo (Citrus limonia Osbeck)

Abstract

The present work describes the study of biosynthesis of pyranocoumarins in Citrus sinensis and Citrus limonia. Coumarins, like other phenylpropanoids, have biosynthetic origin in p-hydroxy cinnamic acid and their great structural diversity is mainly due to the incorporation of prenyl units in the benzene ring. To obtain answers on the prenylation reaction, isotopic labeling experiments were performed to confirm the biosynthesis of pyranocoumarins. To verify if the isopentyl diphosphate (IPP) unit used in the prenylation of umbelliferone in C-6 and C-8, leading to the linear and angular pyranocumarins respectively, comes from the mevalonate (MEV) pathway via 2-C-methyl-D-erythritol- 4-phosphate (MEP), or mixed route; the biosynthesis of the terpene portion of xanthyletin and seselin was investigated by the incorporation of glucose-1 [¹³C] into C. sinensis and C. limonia. For the confirmation of the biosynthetic route, the enrichment pattern was determined by comparing the quantitative ¹³C NMR spectra of xanthyletin and seselin isolated from the C. sinensis and C. limonia root cultured in MS basal medium with 100% glucose and of a second experiment with 75% glucose-1 [¹³C]. The results showed that the isoprene portion derives exclusively from the MEP pathway, because only the C-1 and C-5 carbons of the IPP unit, for both C. sinensis and C. limonia xanthyletin and C. limonia seselin were enriched. By analyzing the chemical profile of the plant parts, the presence of the pyranocoumarins was observed only in the roots of both species, indicating that the biosynthesis of the same occurs in the citrus roots. It was also carried out the quantification of pyranocoumarins in roots, to determine a genotype that presented higher production of this class of compounds. In the quantification of pyranocoumarins in the 12 genotypes of C. sinensis and C. limonia grown in vitro in MS basal medium, it was observed that there is a significant decrease in the production of these substances among the genotypes of each of the evaluated species and that the concentration of these compounds in C. limonia is 158,35% higher than in C. sinensis.