Physiological responses by Billbergia zebrina (Bromeliaceae) when grown under controlled microenvironmental conditions
Sucrose, the most commonly used carbon source in conventional in vitro culture, and limited air exchange in the culture containers are factors that affect the growth of in vitro-cultured plants. They may induce physiological disorders and decrease the survival rate of plants after transfer to ex vitro conditions. The aim of the present study was to analyze the effects of gas exchange and sucrose concentration on Billbergia zebrina plantlets during in vitro propagation. In vitro-established B. zebrina plantlets were transferred to culture media containing 0, 15, 30, 45, or 60 g L-1 sucrose. Two different culture-container sealing systems were compared: lids with a filter (permitting gas exchange) and lids with no filter (blocking fluent gas exchange). Carbohydrate and chlorophyll (Chl a+b) concentrations were analyzed in plantlets at 45-days of culture. The addition of sucrose to the medium reduced the Chl a+b concentration in the plantlets. On the other hand, additional sucrose had a positive effect on the carbohydrate stock formation of the plantlets. The results showed that a photoautotrophic system (air exchange and a sugar-free medium) improves the in vitro propagation of B. zebrina without creating physiological disorders.
Key words: Bromeliad, In vitro plant, photoautotrophic growth, physiological disorders, sucrose.