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Responses of Medicinal Substances in St. John's Wort to Elevated CO2
Mosaleeyanon, K., Zobayed, S.M.A., Afreen, F. and Kozai, T.  2005.  Relationships between net photosynthetic rate and secondary metabolite contents in St. John's wort.  Plant Science 169: 523-531.

The authors note that St. John's wort (a perennial herb native to Europe and West Asia) has been used as "a medicinal plant for the treatments of mild to moderate depression, inflammation and wound healing (Brolis et al., 1998; Stevinson and Ernst, 1999)," and has been reported to be "a potential source for anticancer, antimicrobial and antiviral medicines (Schempp et al., 2002; Pasqua et al., 2003)."  The three substances most often cited in this regard are hypericin, pseudohypericin and hyperforin.

What was done
Mosaleeyanon et al. grew well watered and fertilized St. John's wort seedlings for 45 days in controlled environment chambers at low, medium and high light intensities (100, 300 and 600 Ámol m-2 s-1, respectively) and at atmospheric CO2 concentrations of 500, 1000 and 1500 ppm.  On day 43, they measured net photosynthetic rates in all treatment combinations at plant growth conditions; and on day 45 the plants were harvested and the three medicinal substances (hypericin, pseudohypericin and hyperforin) extracted from their leaves and quantified.

What was learned
Under all three levels of light intensity employed in the study, the 1000-ppm increase in atmospheric CO2 concentration experienced in going from 500 to 1500 ppm led to total plant biomass increases of approximately 32%.  Over this same CO2 concentration range, hypericin concentrations rose by 78, 57 and 53%, respectively, under the low, medium and high light intensities, while corresponding increases in pseudohypericin were 70, 57 and 67% and those in hyperforin were 102, 23 and 3%.  The researchers also found that plots of leaf concentrations of hypericin and pseudohypericin vs. net photosynthesis were well-defined by second order polynomials.  Last of all, compared to results obtained from plants growing out-of-doors in air of 380 ppm CO2 and at light intensities on the order of 1770 Ámol m-2 s-1, Mosaleeyanon et al. report that total plant biomass was fully 30 times greater in the high-light, high-CO2 treatment, while concentrations of hypericin and pseudohypericin were 30 and 41 times greater, respectively, in the high-light, high-CO2 treatment.

What it means
Growing St. John's wort plants at higher-than-normal atmospheric CO2 concentrations in a controlled environment can enormously enhance the production of both plant biomass and total hypericin (hypericin + pseudohypericin) content by increasing plant rates of net photosynthesis.

Brolis, M., Gabetta, B., Fuzzati, N., Pace, R., Panzeri, F. and Peterlongo, F.  1998.  Identification by high-performance liquid chromatography-diode array detection-mass spectrometry and quantification by high-performance liquid chromatography-UV absorbance detection of active constituents of Hypericum perforatumJournal of Chromatography A 825: 9-16.

Pasqua, G., Avato, P., Monacelli, B., Santamaria, A.R. and Argentieri, M.P.  2003.  Metabolites in cell suspension cultures, calli, and in vitro regenerated organs of Hypericum perforatum cv. Topas.  Plant Science 165: 977-982.

Schempp, C.M., Krikin, V., Simon-Haarhaus, G., Kersten, A., Kiss, J., Termeer, C.C., Gilb, B., Kaufmann, T., Borner, C., Sleeman, J.P. and Simon, J.C.  2002.  Inhibition of tumor cell growth by hyperforin, a novel anticancer drug from St. John's wort that acts by induction of apoptosis.  Oncogene 21: 1242-1250.

Stevinson, C. and Ernst, E.  1999.  Hypericum for depression: an update of the clinical evidence.  European Neuropsychopharmacology 9: 501-505.

Reviewed 7 September 2005