Abstract:The chlorophyllous layer of leaf of a PEP-CK type CAM plant Aloe vera was stripped tiff from the colorIess water storage tissue and used to stuly the interrelation between the activity of decarboxylating enzyme phosphoenolpyruvate carboxykinase (PEPCK) and photosynthesis. Oxaloacetate, malate+ADP, and NaHCO3 were found to stimulate photosynthetic oxygen evolution. During the period from 6:00 to 18:00 of the day time, a diurnal fluctuation was observed in both PEPCK activity and the rate of oxygen evolution. The maximum of photosynthesis appeared at 10-12:00, but the maximum PEPCK activity appeared at 14:00. The PEPCK activity and photosynthetic rate in leaf discs increased with temperature from 10 to 35℃, then decreased at 45℃. Similar decline of both parameters was found in the leaf discs stressed by different concentration of PEG-6000 solution for 4.5 h. At light intensity of 900 mol m-2 s-1 and 25℃, the PEPCK activity and photosynthetic rate of leaf discs rised with the illumination time, then a slight inhibition followed at the time of 30 min (Pn) or 40 min (PEPCK). The strong response of PEPCK activity to high light intensity in leaf discs, and a progressive increase of PEPCK activity in direct illumination of crude enzyme extractm the range of 0-55 min, indicated that light s likely to be an activator for PEPCK. Leaf discs were infiltrated with 3-(3,4-dichlorophenyl)-l, 1-dimethylurea, DL-glyceraldehyde and 2,4-dimitrophenol resulted in the partial inhibition of light-ependent photosynthesis and decarboxylation of C4 acid. The activity of PEPCK was also stimulated by Mg2+ or Mg2++ATP infiltrated into the leaf discs in the dark. The evidence presented here suggested that PEPCK activity of CAM plants showed a close interrelation with photosynthesis. Both of them were regulated by the environmental changes. The activity of PEPCK might be coupled to electron trsnsport and photophosphorylatiou.