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The literature on photoautotrophic plant tissue cultures is reviewed and results from experiments reported in which calli of Asparagus officinalis leaves were obtained on Nitsch medium and later transferred to and maintained on Murashige and Skoog medium with 1 mg/litre naphthalene acetic acid and 0·1 mg/litre kinetin. Friable, green calli were selected and replicated to obtain fine chlorophyllous, heterotrophic suspensions of individual cells and small cell aggregates. The carbon source for the suspension was 20 g/litre lactose. Four of these photomixotrophic suspensions were grown in the presence of light and in an atmosphere enriched with 1% CO2. By progressively reducing the lactose concentration continuously or discontinuously over a period of 2–8 weeks, we were able to obtain photoautotrophic growth. The transition from photomixotrophy to photoautotrophy was followed by measuring the oxygen evolution in the presence and absence of light (photosynthesis/respiration estimations). By using continuous culture and by modifying the dilution rate of the culture, we were able to obtain a photoautotrophic strain of A. officinalis with a doubling time of 7 days.

Mesophyll cells have been isolated from Psoralea bituminosa plant by gentle homogenization in a liquid nutrient medium. Between 60 and 70% of the cells can be isolated from leaves using this method, of which 50 to 60% can be recovered morphologically intact. Under light the separated cells have rates of oxygen evolution under light of 3500 μl O2 mg−1 chlorophyll h−1 (measured with a Clark-type electrode). During growth, this rate decreases rapidly, as does cell pigments (chlorophylls and carotenoids). As a first step in obtaining a photoautotrophic cell suspension, growth factors affecting cell division in free sugar medium were investigated. The starting culture contained between 1 and 2 × 106 cells ml−1. The best increase in cell number was obtained on a medium composed of Joshi and Ball's elements and vitamins and containing 1 mg l−1 of naphthalene acetic acid, 0.1 mg l−1 of benzylaminopurine and the grinding juice. The optimum culture pH was between 5 and 5.3.

Summary The aim of this study was to obtain photoautotrophic suspension cultures from Euphorbia characias L., a Mediterranean species with high isoprenoid content. Calluses were initiated in photomixotrophy on a modified Murashige and Skoog (MS) medium supplemented with NAA and BAP. Selection and subculture led to chlorophyllous and friable calluses which were used to initiate suspension cultures. Batch cultures were performed in 250 ml closed conical flasks and analysed with respect to cell density, sugar consumption and chlorophyll content. Cells in the early stationary phase exhibited good photosynthetic potency, allowing transfer into bioreactors where cells have been grown photoautotrophically since February 1984.

Summary Euphorbia characias suspension cultures were used to study the transition from photoheterotrophy to photoautotrophy by in situ measurement of pH, dissolved O 2 and dissolved CO 2 . The culture was able to reversibly alter its metabolism depending on culture conditions. Variation in pH was found to be a direct reflection of the culture's photosynthetic capacity. Photoautotrophic cultures grow at a rate six times slower than photoheterotrophic cultures. Possible limiting factors are discussed with emphasis on photorespiration.

The growth of the hydrocarbon-rich alga Botryococcus braunii was studied under “air-lift” conditions using batch and continuous cultures. Large variations in the physiological state of B. braunii were achieved in batch cultures and in continuous cultures with various dilution rates. The possible effects of these variations upon hydrocarbons (nature, relative abundance, location, level, productivity) and also on the production of exocellular polysaccharides were examined. The relationships between the physiological state of B. braunii and its hydrocarbon and polysaccharide production were discussed and compared with those generally observed in unicellular algae. The factors giving rise to the transition from high to low productivity stages were considered. To this end we examined, at first, the variations in cell ultrastructure and the resulting degeneration occurring during batch cultures. Afterward the parallel changes in some parameters of the medium (pH, phosphate level) were determined and their possible relationships with B. braunii growth and hydrocarbon production were discussed. The main features of phosphate nutrition in B. braunii and its effects on hydrocarbons were finally examined.