Abstract

Studies were performed using ¹⁴C radiolabel to elucidate the extent to which carbon from four sources (CO₂, sucrose, glucose and acetate) contribute to the primary metabolites and alkaloids produced by the roots, stems and leaves of Catharanthus roseus plant. ¹⁴CO₂ derived metabolites were most preferred for biosynthesis of leaf and root alkaloids. Roots were the major accumulators of metabolites accompanied by higher ¹⁴C content into total alkaloids. ¹⁴C-glucose derived metabolites were the second most preferred substrate for leaf and stem alkaloid accumulation and the stem showed highest incorporation into alkaloids. ¹⁴C-sucrose was the third most preferred carbon source for biosynthesis of leaf, stem and root alkaloids. Among these substrates, ¹⁴C-acetate was the least preferred by the plant for biosynthesis of alkaloids of leaf, stem and root. There were variations in the metabolite mobilization of sugars, amino acids and organic acids between leaf, stem and root when different C sources were supplied. A floating metabolic pool seems to influences the alkaloid biosynthesis occurring in leaf, stem and root. The relative higher incorporation of ¹⁴CO_2, ¹⁴C-sucrose and ¹⁴C-glucose suggests the preferential utilization of metabolites from MEP/terpenoid pathway that contribute to alkaloid accumulation as compared to¹⁴C acetate suggesting lower contribution by mevalonate/terpenoid pathway derived metabolites.

Key words: ¹⁴C-Sources, primary assimilate partitioning, Catharanthus roseus, leaf, stem, root, sugars, amino acids, organic acids, total alkaloids.