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Plants produce a variety of secondary metabolites to defend themselves against herbivores or to attract pollinating insects. Plant cell biotechnology offers excellent opportunities in order to use such secondary plant metabolites to produce goods with consistent quality and quantity throughout the year, and therefore to act independently from biotic and abiotic environmental factors. This article presents results of an extensive study of plant cell in vitro cultivation in a modern shake flask system with noninvasive online respiration activity monitoring unit. Comprehensive screening experiments confirm the successful transfer of a model culture (sunflower suspension) into the shake flask monitoring device and the suitability of this respiration activity monitoring unit as qualified tool for screening of plant in vitro cultures (sunflower and sage suspension). The authors demonstrate deviations between online and offline data due to varying water evaporation from different culture flask types. The influence of evaporation on growth‐specific parameters thereby rises with increasing cultivation time. Furthermore, possibilities to minimize the impact of evaporation, either by adjusting the inlet air moisture or by measuring the evaporation in combination with an appropriate correction of the measured growth values are shown.

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Stirred tank-bioreactors made of glass or steel, wave-mixed, and orbitally shaken bag bioreactors have all proven to be suitable for the rapid development and commercial production of bioactive compounds with plant cell suspensions. Although these bag bioreactors are characterized by reduced foam formation and less flotation in comparison to stirred systems, their power input is limited. Engineering parameters such as mixing time, oxygen transfer, and power input are dependent on the viscosity of the liquid and thus, investigations with plant cell suspensions are necessary. However, to save time and achieve better controllability, sodium carboxymethyl cellulose (Na-CMC) solutions in concentrations ranging from 1 to 20 g L −1 , with viscosities of between 0.005 and 0.4 Pa·s, were identified as appropriate model systems for mimicking plant cell suspensions with packed cell volumes of between 30 and 70 % and similar viscosities. The current study has shown that it is possible to transfer a Helianthus annuus cell suspension process from an orbitally shaken CultiBag RM 1 L to a CultiBag RM with a 10 L working volume by adjusting the operating parameters to achieve a constant k L a value. A maximum specific growth rate μ max of around 0.25 d −1 was achieved, which corresponds to optimized data for shake flasks and even exceeds the growth rate for stirred glass bioreactors.

Tocopherols, collectively known as vitamin E, are lipophilic antioxidants, which are synthesized only by photosynthetic organisms. Due to their enormous potential to protect cells from oxidative damage, tocopherols are used, e.g., as nutraceuticals and additives in pharmaceuticals. The most biologically active form of vitamin E is α-tocopherol. Most tocopherols are currently produced via chemical synthesis. Nevertheless, this always results in a racemic mixture of different and less effective stereoisomers because the natural isomer has the highest biological activity. Therefore, tocopherols synthesized in natural sources are preferred for medical purposes. The annual sunflower (Helianthus annuus L.) is a well-known source for α-tocopherol. Within the presented work, sunflower callus and suspension cultures were established growing under photomixotrophic conditions to enhance α-tocopherol yield. The most efficient callus induction was achieved with sunflower stems cultivated on solid Murashige and Skoog medium supplemented with 30 g l(-1) sucrose, 0.5 mg l(-1) of the auxin 1-naphthalene acetic acid, and 0.5 mg l(-1) of the cytokinin 6-benzylaminopurine. Photomixotrophic sunflower suspension cultures were induced by transferring previously established callus into liquid medium. The effects of light intensity, sugar concentration, and culture age on growth rate and α-tocopherol synthesis rate were characterized. A considerable increase (max. 230%) of α-tocopherol production in the cells was obtained within the photomixotrophic cell culture compared to a heterotrophic cell culture. These results will be useful for improving α-tocopherol yields of plant in vitro cultures.