Müller, Viola: Relevance of mineral nutrition and light quality for the accumulation of secondary metabolites in Centella asiatica and Hydrocotyle leucocephala. - Bonn, 2014. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
Online-Ausgabe in bonndoc: https://nbn-resolving.org/urn:nbn:de:hbz:5n-34697
@phdthesis{handle:20.500.11811/5821,
urn: https://nbn-resolving.org/urn:nbn:de:hbz:5n-34697,
author = {{Viola Müller}},
title = {Relevance of mineral nutrition and light quality for the accumulation of secondary metabolites in Centella asiatica and Hydrocotyle leucocephala},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2014,
month = jan,

note = {The key objective of the present work was to acquire fundamental knowledge on the impact of nutrient supply and light quality on the accumulation of pharmaceutically relevant secondary metabolites, particularly saponins and lignans, using Centella asiatica and Hydrocotyle leucocephala as examples. Experiments on the impact of N, P, and K supply on saponin and sapogenin (centelloside) accumulation in leaves of C. asiatica were conducted in the greenhouse using soilless culture. Thereby, the relationship between plant growth and centelloside accumulation as influenced by nutrient supply was investigated. Furthermore, the suitability of fluorescence-based indices for non-destructive tracking of centelloside accumulation in vivo was examined. For this purpose, different levels of N, P, and K supply were selected as experimental factors. In order to investigate the effects of light quality on saponin and lignan accumulation, experiments were conducted in technically complex sun simulators providing almost natural irradiance. Here, we postulated that high intensity of photosynthetic active radiation (PAR) and ambient level of ultraviolet (UV)-B radiation additively promote the accumulation of centellosides in leaves of C. asiatica. The specific UV-B response in terms of flavonoid accumulation was monitored in vivo by fluorescence recordings. Finally, the impact of different PAR/UV-B combinations on the concentration and distribution pattern of selected phenylpropanoids, and in particular the lignan hinokinin, was examined in leaves and stems of H. leucocephala. The results ascertained in the single chapters can be summarized as follows:
1.The higher levels of N, P, or K supply (in the range from 0 to 150% of the amount in a standard Hoagland solution) enhanced net photosynthesis (Pn) and herb and leaf yield of C. asiatica. However, exceeding nutrient-specific thresholds, the high availability of one single nutrient caused lower leaf N concentrations and a decline in Pn and plant growth. Irrespective of N, P, and K supply, the leaf centelloside concentrations were negatively associated with herb and leaf yield. Moreover, negative correlations were found between saponins and leaf N concentrations, and between sapogenins and leaf K concentrations.
2.The accumulation of both flavonoids and anthocyanins was affected by N, P, and K fertigation in the same way as the centelloside accumulation, indicating that limitations in plant growth were generally accompanied by higher secondary metabolite concentrations. The fluorescence-based flavonol (FLAV) and anthocyanin (ANTH_RG) indices correlated fairly with flavonoid and particularly with anthocyanin concentrations. Moreover, the centellosides were positively correlated with the FLAV and ANTH_RG indices, and with the BFRR_UV index, which is considered as universal ‘stress-indicator’. Thus, the indices FLAV, ANTH_RG, as well as BFRR_UV enabled the in situ monitoring of flavonoid and centelloside concentrations in leaves of C. asiatica.
3.UV-B radiation favored herb and leaf production of C. asiatica, and induced higher values of the fluorescence-based FLAV index. Similarly, the ANTH_RG index and the saponin concentrations were raised under high PAR. In contrast, UV-B radiation had no distinct effects on saponin and sapogenin concentrations. In general, younger leaves contained higher amounts of saponins, while in older leaves the sapogenins were the most abundant constituents.
4.The concentration of the selected phenylpropanoids in H. leucocephala depended on the plant organ, the leaf age, the light regimes, and the duration of exposure. The distribution pattern of the compounds within the plant organs was not influenced by the treatments. Based on the chemical composition of the extracts a principal component analysis enabled a clear separation of the plant organs and harvesting dates. In general, younger leaves mostly contained higher phenylpropanoid concentrations than older leaves. Nevertheless, more pronounced effects of the light regimes were detected in older leaves. As assessed, the individual compounds responded very differently to the PAR/UV-B combinations. Hinokinin was most abundant in the stems, where its accumulation was slightly enhanced under UV-B exposure.},

url = {http://hdl.handle.net/20.500.11811/5821}
}

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