芦荟叶片磷酸烯醇式丙酮酸羧激酶活性与光合作用的关系

THE RELATION BETWEEN ACTIVITY OF PHOSPHOENOLPYRUVATE CARBOXYKINASE AND PHOTOSYNTHESIS IN ALOE VERA LEAVES

PCK型的CAM植物芦荟(Aloc vera)叶片表层绿色组织中,磷酸烯醇式丙酮酸羧激酶(PEPCK,EC.4.1.1.49)活性和光合放氧速率呈单峰形日进程变化,中午前后达最大值。温度、水分和不同照光时间皆导致绿色组织圆片中PEPCK活性和光合速率发生类似的变化。OAA,苹果酸+ADP,以及NaHCO_3对光合放氧有促进作用。Mg^(2+)和ATP刺激PEPCK活性。DCMU,DL-甘油醛和DNP抑制光合作用和PEPCK活性。结果表明PEPCK活性和光合作用相互制约,光下PEPCK的活性与电子传递及CO_2消耗有关。

The chlorophyllous layer of Ieaf of a PEP-CK type CAM plant Aloe vera was stripped off from the colorless water storage tissue and used to stuly the interrelation between the activity of decarboxylating enzyme phosphoenolpyruvate carboxykinase (PEPCK) and photosyn- thesis. Oxaloacetate, malate+ADP, and NaHCO_3 were found to stimulate photosynthetic oxy gen evolution. During the period from 6:00 to l8:00 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 u 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 extract in 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)-1, 1-dimethylurea, DL-glyceraldehyde and 2,4-dimitrophenol resulted in the partial inhibition of light-dependent photosynthesis and decar- boxylation of C_4 acid. The activity of PEPCK was also stimulated by Mg^(2+) or Mg^(2+)+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 transport and photophosphorylation.