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The kinetics of tropane alkaloid biosynthesis, particularly the isomerization of littorine into hyoscyamine, were studied by analyzing the kinetics of carbon-13 (¹³C) in metabolites of Datura innoxia hairy root cultures fed with labeled tropoyl moiety precursors. Both littorine and hyoscyamine were the major alkaloids accumulated, while scopolamine was never detected. Feeding root cultures with (RS)-phenyl[1,3-¹³C2]lactic acid led to ¹³C spin−spin coupling detected on C-1‘ and C-2‘ of the hyoscyamine skeleton, which validated the intramolecular rearrangement of littorine into hyoscyamine. Label from phenyl[1-¹³C]alanine or (RS)-phenyl[1,3-¹³C2]lactic acid was incorporated at higher levels in littorine than in hyoscyamine. Initially, the apparent hyoscyamine biosynthesized rate (vapphyo = 0.9 μmol ¹³C·flask^-1·d^-1) was lower than littorine formation (vapplitto = 1.8 μmol ¹³C·flask^-1·d^-1), suggesting that the isomerization reaction could be rate limiting. The results obtained for the kinetics of littorine biosynthesis were in agreement with the role of this compound as a direct precursor of hyoscyamine biosynthesis.

The cytochemical demonstration of acetylcholinesterase is theoretically and experimentally evaluated with a model system. The model is an artificial proteic membrane in which acetylcholinesterase homogeneously is immobilized chemically by a bifunctional agent, glutaraldehyde. The copper-thiocholine histochemical method is studied kinetically and the system is simulated by computer calculations based on experimental kinetic parameters and numerical analysis methods. In addition, the corresponding electron micrographs are presented. These studies lead to the conclusions that the system is ruled by diffusional constraints and that enzyme distribution and repartition of the insoluble electron dense product are not circumscribed by any specific conditions.

Methods to encapsulate biological materials are now widely used. Sometimes biocncapsulation is considered as a universal technique conducing to identical results independently on the biological material used. For instance, a similar behavior is frequently waited for different strains of immobilized microorganisms without taking into account substantial differences in its physiological and morphological characteristics. Often interactions with the matrix support are also neglected. Thus, some concepts developed throughout all these years working in bioencapsulation merits to be revisited.

Somatic embryos are characterised by the absence of any protection, a very low reserve level and a high water content. The effects on the respiration and the radicular elongation of somatic embryos of a non tonic and easy to use hydrogel, such as alginate, have been studied. Respiration or germination rates decreased with an increase in alginate concentration. When the encapsulated somatic embryos were placed in a liquid medium, there was very little difference between the germination rates observed at different alginate concentrations, either with or without an additional PEI layer. The effect of capsule concentration on germination rate was significatively different when the artificial seeds were growing on solid media. Besides the anoxic treatment upon encapsulated somatic embryos, storage for one month also decreased the germination rate.