A Possible Induction of CAM by NaCl-Stress in Heterotrophic Cell Suspension Cultures of Mesembryantbemum crystallinum

Abstract

Summary NaCl-induced stress in cell suspension cultures of the facultative CAM plant M. crystallinum caused an increase of PEPcase activity which yet was distinctly less than the activation of the enzyme in the whole plants under salt stress. The activation was obtained after both long-term and shock treatments with salt. Immunotitration revealed that more PEPcase protein was present in the stressed cells compared with the non-stressed controls. This demonstrates that the observed increase of PEPcase activity was due to a de novo synthesis of the enzyme. Moreover, the identical appearance of the immunotitration curves suggests that the ratio of PEPcase protein to PEPcase activity was identical and that the serological characteristics of PEPcase protein were virtually the same in stressed and non-stressed cells. The label distribution among metabolites after 14 CO 2 fixation showed that the degree of labelling did not depend on NaCl pretreatments of the cells. Malate was always the main labelled product. Total 14 C incorporation rates were higher in the unstressed cells. The absolute malate content was slightly increased in the salt treated cells. The present results show that also in cell cultures of M. crystallinum salt stress leads to an increase in the potential activity of PEPcase and in the malate levels. Therefore it can be concluded that salt stress can directly stimulate the biochemical pathway of PEP-carboxylation involved in CAM, though the whole CAM syndrome cannot be expressed in the case of heterotrophic suspension cells, due to the culture conditions.