Physiological and biochemical changes during acclimatization in a Doritaenopsis hybrid cultivated in different microenvironments in vitro

• We cultivated Doritaenopsis plantlets (CAM-type photosynthesis) in vitro under three different microenvironmental conditions and transferred in ex vitro conditions.
• We examine the changes in growth, physiological and biochemical factors during acclimatization of those plantlets.
• Photoautotrophically and photomixotrophically grown plants in in vitro exhibited the best growth in the ex vitro environment.
• May be a consequence of the presence of higher sugar reserves in these plants, as well the early recovery of PEP-carboxylase activity.

Photoautotrophic culture has advantages over conventional micropropagation methods, and its potential benefits appear to be promising. Nevertheless, little is known regarding the effects of such culture conditions on plant physiology during ex vitro acclimation. In this study, Doritaenopsis plantlets were grown under three different microenvironmental conditions: (1) in vitro under photoautotrophic conditions (high photosynthetic photon flux density [PPFD], high CO2 concentrations and an increased number of air exchanges), (2) photomixotrophic conditions (photoautotrophic conditions, with 30 g L−1 sucrose added to the culture medium) and (3) heterotrophic conditions (conventional culture conditions; low PPFD, low CO2 concentration and no air exchange). The plantlets were subsequently transferred into ex vitro conditions, and the physiological and biochemical changes were investigated during the acclimation process. Photoautotrophic and photomixotrophic in vitro cultivation markedly stimulated the growth of Doritaenopsis plantlets during ex vitro acclimatization. The development of photosynthetic function (PEP-carboxylase activities and carbohydrate metabolism) appeared to be fully achieved in ex vitro plantlets that had been cultured in photoautotrophic and aerated photomixotrophic conditions in vitro. The strong enhancement of growth by CO2 enrichment, along with the exposure of photoautotrophic plantlets to high PPFD, may explain why the plants adjust more effectively (exhibiting higher rates of photosynthesis under high-light conditions) during ex vitro acclimatization. The results of this study suggest that the growth and survivability of Doritaenopsis during the acclimatization process can be enhanced by CO2 supplementation and increased light levels during in vitro culture.