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L'interaction de la lumière et de la température ainsi que l'effet de l a photopériode sur la croissance de Chlorella sorokiniana sont étudiés en milieu fini et en conditions nutritives non limitantes. Le taux maximal de croissance (2,7 j 1 ) est enregistrée la température d e 35°C, sous une intensité de 300 ^E.m-2 .s-' et en éclairement continu. L'ensemble des données est repris sous la forme d'un modèle mathématique qui permet d'estimer le taux d e croissance d e la culture en fonction des conditions environnementales.The influence o f daylength, light intensity and temperature on the growth rate o f Chlorella sorokiniana Shih. e t kraus.Keywords : Chlorella sorokiniana, growth rate, light, temperature, daylength.The light and temperature interactions and the effect of daylength on the growth rate of Chlorella sorokiniana were studied i n batches and in non-nutrient-limited conditions. The maximum growth rate (2.7 d 1 ) was recorded a t a temperature o f 35°C, light intensity o f 300 ^E.m^.s-1 and continuous light. The results were adjusted by a mathematical model which can b e used t o estimate the growth rate o f a culture in relation t o environmental conditions.

The effects of irradiance and photoperiod on the growth rate of three freshwater green algae isolated from a eutrophic lakeIn order to optimise algal growth in mass culture systems, the effect of irradiance and photoperiod on the growth rate of three freshwater green algae isolated from an eutrophic lake (Selenastrum minutum, Coelastrum microporum f. astroidea and Cosmarium subprotumidum) were studied in non axenic batch cultures, under non-nutrient limited conditions. Experiments were performed to determine a specific growth rate (µ max) and optimum light (Iopt) over a wide range of light intensities (30 to 456 µmol m 2 s −1 ) at a temperature of 30 • C, using a 15/9 (light/dark) photoperiod cycle. The maximum growth rates and optimum light intensities were 1.55 d −1 and 365 µmol m −2 s −1 for Selenastrum minutum, 1.59 d −1 and 390 µmol m −2 s −1 for Coelastrum microporum f. astroidea 0.88 d −1 and 360 µmol m −2 s −1 for Cosmarium subprotumidum. The photoperiod's effect was determined at 30 • C and an incident light of 300 µmol m −2 s −1 , under various light:dark cycles. The experimental values fitted by models of Belkoura et Dauta (1992) indicate an increase in the growth rate versus day length with a maximum at continuous light (1.84 d −1 for Selenastrum minutum, 1.72 d −1 for Coelastrum microporum f. astroidea, 0.88 d −1 for Cosmarium subprotumidum). However these experiments don't take into account the accumulated light intensities received by each culture (period of incubation: 24 hours). It was, therefore, not possible to independently appraise the real effect of the lengthened irradiance exposure. So more experiments were carried out, where all cultures under different (light/dark) photoperiod cycles at 30 • C received the same cumulated irradiance (8.6 mol m −2 d −1 ). The results showed that the growth rate is not constant but increased with day length with a maximum at continuous light. These results confirm the real effect of photoperiod on the microalgae growth rate.

During growth, cultured Catharanthus oseus cells produce a transient acidification of the culture medium that may be controlled by cations. The removal of divalent ions from the medium by the chelator EGTA resulted in an inhibition of this acidification. Conversely, acidification can be stimulated by the addition of Ca2+, Mg2+ and La3+ in the basal medium. This acidification process and the proton‐linked redox pump previously described (Marigo & Belkoura, 1985) respond in a similar manner to cations. These two systems, which are both inhibited by the Ca2+ ‐calmodulin antagonist calmidazolium, could be regulated by the Ca2+‐calmodulin complex. By using ionic surfactant (CP+, SDS−) it was demonstrated that the net surface charge of the plasmalemma plays a role in the activation of the two pumping processes. These results are interpreted to indicate that a transmembrane redox system could provide the energy for electrogenic proton extrusion.