Effects of light intensity on growth and accumulation of triterpenoids in three accessions of Asiatic pennywort (Centella asiatica (L.) Urb.)

摘要

This study deals with the effects of light and accessions on leaf area, petiole length and accumulation of asiaticoside, madecassoside, asiatic acid and madecassic acid that were studied in three accessions of Asiatic pennywort (Centella asiatica (L.) Urb.). The accessions of C. asiatica, Nakon Si Thammarat, Rayong and Ubon Ratchathani, were collected from three different locations in Thailand and planted at the Thailand Institute of Scientific and Technological Research in Pathum Thani Province. They were grown for 90 days in replicated organic culture system under different light intensities expressed as photosynthesis photon flux densities (PPFD) (933.1 (full sun light), 362.5 and 93.3 mu mol m(-2)s(-1), respectively). Light intensities and accessions affected leaf area, petiole length, fresh and dry weight, asiaticoside, madecassoside, asiatic acid and madecassic acid content. At high light intensity, leaf area and petiole length were smaller than at low light intensity in each accession. The Nakhon Si Thammarat accession had the largest leaf area followed by the Ubon Ratchathani and Rayong accessions, respectively, while the longest petioles were found in Rayong, and Ubon Ratchathani had the highest fresh weight per unit area. Dry weight per kg fresh weight did not differ with genotype. With decreasing light intensity, there was increase in leaf area and petiole length, which differed with genotype, but decrease in fresh and dry weights, which did not vary much with genotype. Triterpenoid analysis by High Performance Liquid Chromatography (HPLC) revealed varying genotypic responses to light intensity. Asiaticoside and madecassoside contents were highest in Ubon Ratchathani and comparably lower in Nakhon Si Thammarat and Rayong. Low light intensity reduced the content of both triterpenoids in all genotypes, with Ubon Ratchathani exhibiting more pronounced decreases. Asiatic acid content did not differ with genotype while madecassic acid was highest in Nakhon Si Thammarat followed by that of Ubon Ratchathani and Rayong, respectively. With decreasing light incidence, asiatic acid content decreased in Nakhon Si Thammarat only under full sunlight (PPFD value 93.3 mu mol m(-2)s(-1)) while in Ubon Ratchathani, under both 50% and 80% shading (PPFD value 362.5 and 933.1 mu mol m(-2)s(-1)). Madecassic acid contents showed almost similar response to low light intensities. Contrastingly in Rayong, asiatic and madecassic acid contents remarkably increased under 50% shading (PPFD value 362.5 mu mol m(-2)s(-1)). The results demonstrate genotypic variations in growth characteristics and triterpenoid contents and the detrimental effect of low light intensity on contents of asiaticoside and madecassoside, the main pharmacologically active triterpenoids of C. asiatica.