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The Effects of Elevated CO2 on Medicinal Substances Found in St. John's Wort Plants
Zobayed, S. and Saxena, P.K.  2004.  Production of St. John's Wort plants under controlled environment for maximizing biomass and secondary metabolites.  In Vitro Cellular and Developmental Biology - Plant 40: 108-114.

St. Johns' wort (Hypericum perforatum L.) is a medicinal plant that produces a number of substances (hypericin, pseudohypericin and hyperforin being the principal examples) that have long been used for treating mild depression in cases where standard antidepressants may be prescribed.  In addition, it has recently been demonstrated to possess anticancer properties (Schempp et al., 2002).

What was done
The authors grew transplanted shoots of the "New Stem" cultivar of St. John's wort for 42 days under well-watered and fertilized conditions in a greenhouse, where the air's CO2 concentration averaged 360 ppm during the photoperiod, and in computer-controlled environment chambers maintained at a mean photoperiod CO2 concentration of 1000 ppm, with all other environmental conditions being comparable between the two CO2 treatments.

What was learned
On the last day of the study, net photosynthetic rates of the plants in the CO2-enriched chambers were 124% greater than those of the plants growing in ambient air, while their dry weights, which were determined immediately thereafter, were 107% greater.  In addition, although the elevated CO2 had no effect on plant concentrations of hyperforin, the extra 640 ppm of CO2 in the high-CO2 treatment increased the plant concentrations of both hypericin and pseudohypericin by just over 100%.

What it means
An approximate 180% increase in the air's CO2 content more than doubled the dry mass produced by well-watered and fertilized St. John's wort plants, while it also more than doubled the concentrations of both hypericin and pseudohypericen found in their tissues, which means that the CO2 increase more than quadrupled the total production of these two health-promoting substances.  This study thus joins several others we describe in our Major Report - Enhanced or Impaired? Human Health in a CO2-Enriched Warmer World - as an excellent example of what elevated levels of atmospheric CO2 can do for medicinal and health-promoting plants: a lot!

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 tumour cell growth by hyperforin, a novel anticancer drug from St. John's wort that acts by induction of apoptosis.  Oncogene 21: 1242-1250.

Reviewed 14 July 2004