Studies on the regulating mechanism of CAM photosynthesis under high night temperature

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When a night temperature higher than 36ﾟC was maintained, Kalanchoe daigremontiana and K.pinnata shifted from the CAM photosynthesis to C3 photosynthesis, but Ananas comosus did not alter its photosynthesis. In this study, the shifting mechanism from CAM to C3 was investigated on the aspect of glycolysis regulation. ATP-dependent phosphofructokinase (PFK) of the two Kalanchoe species exhibited an optimum temperature of the activity at 35'C, but PPi-dependent PFK of A.comosus increased the activity up to 40ﾟC.PPi-PFK of A.comosus exhibited two optimum peaks of pH7.2 and 7.6, and ATP-PFK of the Kalankoe species showed an optimum pH of 7.6. Isoelectric point of A.comosus PPi-PFK was changed from two type of pH4.88 and 5.34 in day-form to one type of pH4.80 in night-form. PPi-PFK of A.comosus was eluted as two peaks on DEAB-cellulose column chromatography in both day and night. Each PPi-PFK protein showed ca. 14 mm. and ca. 12 mm. of elution time on size-exclusion chromatography. However, the PPi-PFK protein with large charge density on ion-chromatography was separated to the two proteins. Under high night temperature condition, the increase of glucose 6-phosphate content, which was known as an activator of PEPcase, was depressed in Kalanchoe. As shown above, it was suggested that the glycolysis played an important role in the regulation of CAM photosynthesis.