CO2-enriched atmosphere and supporting material impact the growth, morphophysiology and ultrastructure of in vitro Brazilian-ginseng [Pfaffia glomerata (Spreng.) Pedersen] plantlets

This study aimed to evaluate under photoautotrophic conditions the effect of CO2-enriched atmosphere (360 or 1,000 mu mol CO2 mol(-1) air) combined with two substrate types (agar or Florialite(A (R))) in vitro on plants of Pfaffia glomerata, an endangered medicinal species with promising applications in phytotherapy and phytomedicine. The effects of the treatments on the growth, stomatal density, Rubisco activity, carbon isotopic discrimination, metabolite accumulation, photosynthetic pigments and ultrastructural characteristics were investigated. After a 35-day cultivation period, the in vitro-growth of P. glomerata nodal segments under the different treatments resulted in plants with substantial differences in relation to their growth, photosynthetic pigments, stomatal density and leaf ultrastructural characteristics. The enrichment with CO2 coupled with a porous substrate increased the growth of P. glomerata. The stomatal density in the abaxial epidermis more than doubled in response to the high CO2 supply in both supporting types, whereas the Rubisco activity and activation state were both unresponsive to the treatments. Regardless of the CO2 supply, the plants grown in agar displayed higher carbon isotope discrimination than their counterparts grown in Florialite(A (R)). We propose that the long-term photosynthetic performance was improved using Florialite(A (R)) as a growth support in combination with a high CO2 supply. No apparent signs of photosynthetic down-regulation could be found under elevated CO2 conditions. The enrichment of in vitro atmospheres with CO2 coupled with a porous substrate offers new possibilities for improving the growth and production on a commercial scale of high morphological and physiological quality Pfaffia plants.