Number of air exchanges, sucrose concentration, photosynthetic photon flux, and differences in photoperiod and dark period temperatures affect growthof Rehmannia glutinosa plantlets in vitro

Rehmannia glutinosa plantlets were cultured for 4 weeks under different cul ture conditions to determine the optimum environment for in vitro growth an d ex vitro survival. Plantlet growth increased with an increasing number of air exchanges of the culture vessel, exhibiting greatest shoot weight, tot al fresh weight, leaf area, and chlorophyll content at 4.4 h(-1) of air exc hanges. High sucrose concentration (30 g l(-1)) increased root weight but r educed shoot growth. Net photosynthetic rates of the plantlets were greates t when sucrose was not added to the medium. On the other hand, ex vitro sur vival of the plantlets was not influenced by sucrose concentration. In the experiment on difference in photoperiod and dark period temperatures (DIF) and photosynthetic photon flux (PPF), plantlet growth increased as DIF and PPF levels increased. Particularly, increasing PPF level had a more distinc tive effect on plantlet growth than increasing DIF level. The interaction o f DIF x PPF was also significant, showing the greatest plantlet growth in p ositive DIF (+8 DIF) and a high PPF (210 mu mol m(-2) s(-1)). In conclusion , the results of this experiment suggest that increased number of air excha nges of the culture vessel, decreased sucrose concentration, and positive D IF in combination with high PPF level enhanced growth and acclimatization o f Rehmannia glutinosa plantlets.