The physiology of Cymbidium plantlets cultured in vitro under conditions of high carbon dioxide and low photosynthetic photon flux density

Cymbidium plantlets were grown in vitro under conditions of high CO2 and lo w photosynthetic photon flux density using the Miracle Pack(R) culture syst em. Shoots and roots of plantlets showed differential growth characteristic s. Shoot growth was not different in plantlets cultured under CO2-enriched (CDE) and non-enriched (NCDE) conditions. Root growth was promoted in plant lets cultured under CDE in the presence or absence of 2% sucrose (S) with r ockwool (R) as the supporting material. Growth was poor in plantlets cultur ed in 1% agar, Root growth was best in plantlets cultured under CDE R;S. Su crose is still an important component for root growth under CDE conditions even though CO2 can be used as an alternative carbon source. Photosynthetic measurements (CO2 uptake and total Rubisco activity) showed the presence o f active and operational photosynthetic machinery in plantlets cultured und er CDE and NCDE conditions. The apparent lack of photoautotrophy (as eviden t from the lack of starch grains in chloroplasts) in plantlets cultured und er NCDE conditions is not the result of a lesser potential for photoautotro phy; rather it is a consequence of sub-optimal CO2 concentrations within th e culture vessels.