光合作用的CO_2阶跃响应动态生化模型

A Dynamic Biochemical Model for Photosynthetic Response to CO_2 Step Changes

针对CO2阶跃变化下光合动态响应的振荡现象,依据经典的光合系统酶触反应动力学,初步尝试构建了光合系统反馈控制动态生化模型。该模型以卡尔文环的核酮糖-1,5-二磷酸羧化/加氧酶(ribulose-1,5-bisphosphate carboxylase/oxygenase,Rubisco)接触反应的酶动力学进程作为核心,以磷酸甘油酸(phosphorylglyceric acid,PGA)还原和接续的核酮糖-1,5-二磷酸(ribulose-1,5-bisphosphate,RuBP)再生的多级过程高度简化为复合酶接触反应的酶动力学进程为反馈,构成反馈控制系统。采用经典的控制系统传递函数分析手段,将反馈控制系统表达为光合动态生化模型传递函数。据此模型将实测羧化速率Vc振荡动态进行仿真拟合,呈现出很高的拟合度(r=0.9377)。这表明,在卡尔文环或者光合系统反馈环中,因RuBP的消耗和再生补充不平衡引起的光合振荡现象,与光合系统酶接触反应动力学参数(k)造成各个中间产物再生的"滞后"效应有关。从而在机理上解释了Laisk和Walker(1986)的无机磷(inorganic phosphate,Pi)再生供应的光合动态生化模型中,需要假定代谢途径中蔗糖合成"滞后15～20s"才能表现出光合振荡效果的现象。

According to classical enzyme kinetics of photosynthetic processes,a dynamic biochemical model,comprising key pathway catalyzed by rubisco（ribulose-1,5-bisphosphate carboxylase/oxygenase） in Calvin cycle and feedback loop controlled by a simply multiple enzyme instead of complicated high-order biochemical pathways from the reduction of PGA（3-phosphoglycerate） to regeneration of RuBP（ribulose-1,5bisphosphate）,was formulated on the basis of oscillation in photosynthesis generated by CO2 step change.Ultimately,by using the Transfer Function Analysis（TFC） method,the transfer function was converted from feedback controlled system model into dynamic biochemical model.The results of numerical simulations by the dynamic biochemical model were fairly consistent with the measured rate of carboxylation（Vc）（r = 0.9377＊＊）,which indicated that lagging effect of differential intermediates regeneration ascribed to the enzyme kinetics parameters（k） is responsible for oscillatory photosynthesis caused by imbalance between consumption and regeneration of RuBP either in the Calvin cycle or feedback loop of leaf photosynthesis,respectively.It also accommodated the possibly mechanistic interpretations for the phenomenon of oscillation in photosynthesis,which could be occurred if modulation of sucrose synthesis was assumed to proceed with a time-lag of about 15-20 s in the research of rate of photosynthesis limited by organic phosphates（Pi）.