Effect of CO2 and light on survival and growth of rice regenerants grown in vitro on sugar-free medium

Rice (Oryza sativa L.) plantlets regenerated from callus (rice regenerants) were grown in vitro during the preparation stage either on a 1/4 strength N6 gellan gum (4 g 1(-1)) medium without sucrose (SFM) or with 30 g 1(-1) sucrose (SCM), and under CO2 concentrations of 0.4, 2, 10, 50 or 100 mmol mol(-1), a photoperiod of 24 h and a photosynthetic photon flux density (PPFD) of 125 mu mol m(-2) s(-1). Rice regenerants were also grown in vitro on SFM or SCM under CO2 concentration of 50 mmol mol(-1), a photoperiod of 12 or 24 h and a PPFD of 80 or 125 mu mol m(-2) s(-1). All rice regenerants grew successfully on SFM under CO2 concentrations of 50 or 100 mmol mol(-1). Increasing the CO2 concentration increased the survival percentage, shoot length and shoot and root dry weights of rice regenerants grown on SFM. Increasing CO2 concentration had no significant effect on the survival or growth of rice regenerants grown on SCM. Survival percentages of rice regenerants grown on SCM were less than 80% for each of the CO2 concentrations. A photoperiod of 24 h under CO2 enrichment improved the survival and growth of rice regenerants grown on SFM, and increased the survival percentage and shoot dry weight of rice regenerants grown on SCM.