水分胁迫对露花叶片中PEP羧化酶活性及其调节特性的影响

The Effect of Water Stress on the Level of Phosphoenolpyruvate Carboxylase in the Leaves of Mesembryanthemum cordifolium and Its Regulatory Properties

水分胁迫期间露花叶片中PEP羧化酶的活力随胁迫时间的延长明显增加,复水后PEPC同工酶的活力下降。从露花叶片中分离到3个具有不同动力学和物理学特性的PEPC同工酶(PCⅠ,PCⅡ,PCⅢ),其中同工酶PCⅠ只存在于水分胁迫下露花叶片中,复水后消失。 这3个同工酶的K_m(PEP)值不相同;PCⅠ的K_m(PEP)值介于PCⅡ与PCⅢ之间,它在PAGE上的相对迁移率(Rm)比PCⅡ和PCⅢ大,对效应剂G—6—P及Mal的反应不敏感,分子量为PCⅡ之半;PCⅡ被G—6—P激活和被Mal抑制的程度介于PCⅠ与PCⅢ之间,它在PAGE上的相对迁移率和分子量与PCⅢ极相近。

In contrast to constitutive CAM plantswhich always possess the metabolic machinerynecessary for the performance of CAM inexpanded leaves, inducible CAM plants pre-sumably develop the required mechanisms inresponse to some environmental signal suchas water stress. PEPC (EC 4.1.1.31.) isa key enzyme in CAM. Here are someresults of our experiments on PEPC in M.cordifolium. 1. The activity of PEPC in leaves incre-ased markedly with the aggravation of waterstress. It was 11.4 times greater in plantswater-stressed for 3-weeks than in unstressedplants. It began to decrease when the stres-sed plants were rewatered, falling to nearlythe same level as that in control leaves 19days after being watered. 2. Three protein peaks with PEPC acti-vity (PC Ⅰ, PC Ⅱ, PC Ⅲ) were separated fromwater-stressed leaves of M. cordifolium byDEAE-52 cellulose column chromatography,of which PCI was not found in non-stressedplants. During water stress, the activity ofPC Ⅱ, but not that of PC Ⅲ, increased mar-kedly. PCI appeared after drought treat-ment and disappeared after rewatering. Allthree isozymes were activated by G6p andinhibited by malate, The K_m (PEP) ofPC Ⅰ, PC Ⅱ and PC Ⅲ were 0.54 mmol / L,1.54 tnmol/L and 0.31 mmol/L, respecti-vely. In PAGE, PC Ⅰ moved faster towardsanode than PC Ⅱ and PC Ⅲ. The apparent molecular masses deter-mined by gel concentration gradient electro-phoresis were 130 kD, 260 kD and 275 kDfor PC Ⅰ, PC Ⅱ and PC Ⅲ, respectively, al-though the mobilities of PC Ⅱ and PC Ⅲduring PAGE were much the same, whetherPC Ⅰ was newly synthesized under water stressor was a dissociative product of PC Ⅱ orPC Ⅲ is under investigation.