Micro-propagation techniques contribute to the multiplication of several bromeliad species. However, micropropagated plantlets often present low survival rate due to anatomical and physiological disorders induced by in vitro conditions. This study aimed to evaluate the sucrose and gas exchange impact on in vitro propagated Billbergia zebrina plants and to check if there is any residual effect of the in vitro conditions on micropropagated plants after acclimatization. Previously in vitro-established B. zebrina plants were transferred to culture media containing 0.0, 15.0, 30.0, 45.0 or 60.0 g L -1 sucrose. Two different culture container sealing systems were tested: lids with a filter (permitting an excellent gas exchange) and a filter covered with PVC (blocking fluent gas exchange). At 45 days in vitro growth, B. zebrina plantlets were transplanted onto plastic pots containing peat and cultivated for 80 days in greenhouse. At 45 days in vitro and 80 days of acclimatization in the greenhouse, the plants were evaluated. High sucrose levels in the in vitro media resulted in reduced growth. Plantlets exposed to aerated containers presented better rooting, being the sugar-free medium the best in vitro condition (photoautotrophic condition). Limited air exchange resulted in plantlets with anatomical and physiological disorders at the end of the in vitro period. The highest growth rate in the greenhouse was observed in plants previously propagated in unlimited gas exchange system and sugar-free medium. The use of photoautotrophic conditions induces B. zebrina plantlets without anatomical and physiological disorders and it interfere positively on ex vitro growth.

Throughout the different seasons Aechmea 'Maya' showed considerable plasticity in the timing and magnitude of C(3) and C(4) carboxylation processes over the diel cycle. Under low PPFD (i.e. winter and autumn) it appears that there was a constraint on the amount of carbohydrate exported during the day in order to maintain a consistent pool of transient carbohydrate reserves. This gave remarkable seasonal consistency in the amount of storage reserves available at night, thereby optimizing biomass gain throughout the year. The data have important practical consequences for horticultural productivity of CAM plants and suggest a scenario for reconciling carbohydrate partitioning between competing sinks of nocturnal acidification and export for growth.

Despite the increased size of the soluble sugar storage pool under elevated CO(2), there was no change in the net allocation of carbohydrates between provision of substrates for CAM and export/respiration in A. 'Maya'. The data imply the existence of discrete pools of carbohydrate that provide substrate for CAM or sugars for export/respiration. The 2-fold increase in water-use efficiency could be a major physiological advantage to growth under elevated CO(2) in this CAM bromeliad.

CAM requires a substantial investment of resources into storage carbohydrates to account for nocturnal CO(2) uptake, thereby restricting carbohydrate partitioning to other metabolic activities, including dark respiration, growth and acclimation to abiotic stress. Flexible modulation of carbon flow to the different competing sinks under changing environmental conditions is considered a key determinant for the growth, productivity and ecological success of the CAM pathway. The aim of the present study was to examine how shifts in carbohydrate partitioning could assure maintenance of photosynthetic integrity and a positive carbon balance under conditions of increasing water deprivation in CAM species. Measurements of gas exchange, leaf water relations, malate, starch and soluble sugar (glucose, fructose and sucrose) contents were made in leaves of the CAM bromeliad Aechmea 'Maya' over a 6-month period of drought and subsequently over a 2-month period of recovery from drought. Results indicated that short-term influences of water stress were minimized by elevating the level of respiratory recycling, and carbohydrate pools were maintained at the expense of export for growth while providing a comparable nocturnal carbon gain to that in well-watered control plants. Longer term drought resulted in a disproportionate depletion of key carbohydrate reserves. Sucrose, which was of minor importance for providing substrate for the dark reactions under well-watered conditions, became the major source of carbohydrate for nocturnal carboxylation as drought progressed. Flexibility in terms of the major carbohydrate source used to sustain dark CO(2) uptake is therefore considered a crucial factor in meeting the carbon and energy demands under limiting environmental conditions. Recovery from CAM-idling was found to be dependent on the restoration of the starch pool, which was used predominantly for provision of substrate for nocturnal carboxylation, while net carbon export was limited. The conservation of starch for the nocturnal reactions might be adaptive with regard to responding efficiently to a return of water stress.

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.