Induction of Light Dependent Pyruvate Transport into Chloroplasts of Mesembryanthemum crystallinum by Salt Stress

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Mode of photosynthesis in Mesembryanthemum crys-tallinum changes from C_3 to Crassulacean acid metabolism (CAM) when the plants were stressed with high salinity. [^<14>C]Pyruvate uptake for 30 s into intact chloroplasts isolated from leaves of the CAM mode of M. crystallinum was enhanced more than 5-fold in the light compared with that in the dark. The stromal concentration of pyruvate in the light reached to more than 2.5 times of the medium. In con-trast, little or no pyruvate uptake occurred in chloroplasts from C_3 leaves in either light or dark condition. The initial uptake rate (10 s incubation at 4℃ into the CAM chloroplasts in the light was about 3-fold higher than the rate in the dark. K_m and V_<max> of the initial uptake in the light were 0.54 mM and 8.5 μmol (mg Chl)^<-1> h^<-1>, respectively. These suggest that pyruvate was actively incorporated into the CAM chloroplasts against its concentration gradient across the envelope in the light. When hydroponically grown M. crystallinum were stressed by 350 mM NaCl, the capacity of chloroplasts for pyruvate uptake was induced in 6 d corresponding to the induction of the activities of PEP-carboxylase and NAD(P)^+-malic enzymes in response to salt stress.
日本植物生理学会の論文