Zhu Xin-Guang, Baker Neil R, deSturler Eric, Ort Donald O, Long Stephen P
Department of Plant Biology and Crop Sciences, University of Illinois at Urbana-Champaign, 379 Madigan Laboratory, 1201 W. Gregory Drive, Urbana, IL 61801, USA.
Planta. 2005 Dec;223(1):114-133. doi: 10.1007/s00425-005-0064-4.
Chlorophyll a fluorescence induction (FI) is widely used as a probe for studying photosynthesis. On illumination, fluorescence emission rises from an initial level O to a maximum P through transient steps, termed J and I. FI kinetics reflect the overall performance of photosystem II (PSII). Although FI kinetics are commonly and easily measured, there is a lack of consensus as to what controls the characteristic series of transients, partially because most of the current models of FI focus on subsets of reactions of PSII, but not the whole. Here we present a model of fluorescence induction, which includes all discrete energy and electron transfer steps in and around PSII, avoiding any assumptions about what is critical to obtaining O J I P kinetics. This model successfully simulates the observed kinetics of fluorescence induction including O J I P transients. The fluorescence emission in this model was calculated directly from the amount of excited singlet-state chlorophyll in the core and peripheral antennae of PSII. Electron and energy transfer were simulated by a series of linked differential equations. A variable step numerical integration procedure (ode15s) from MATLAB provided a computationally efficient method of solving these linked equations. This in silico representation of the complete molecular system provides an experimental workbench for testing hypotheses as to the underlying mechanism controlling the O J I P kinetics and fluorescence emission at these points. Simulations based on this model showed that J corresponds to the peak concentrations of Q(-)AQB (QA and QB are the first and second quinone electron acceptor of PSII respectively) and Q(-)AQ(-)B and I to the first shoulder in the increase in concentration of Q(-)AQ(2-)B. The P peak coincides with maximum concentrations of both Q(-)AQ(2-)B and PQH2. In addition, simulations using this model suggest that different ratios of the peripheral antenna and core antenna lead to differences in fluorescence emission at O without affecting fluorescence emission at J, I and P. An increase in the concentration of QB-nonreducing PSII centers leads to higher fluorescence emission at O and correspondingly decreases the variable to maximum fluorescence ratio (F v/F m).
叶绿素a荧光诱导（FI）被广泛用作研究光合作用的探针。在光照下，荧光发射通过称为J和I的瞬态步骤从初始水平O上升到最大值P。FI动力学反映了光系统II（PSII）的整体性能。尽管FI动力学通常很容易测量，但对于控制特征性瞬态系列的因素尚无共识，部分原因是当前大多数FI模型关注的是PSII反应的子集，而非整体。在此，我们提出了一个荧光诱导模型，该模型包括PSII及其周围所有离散的能量和电子转移步骤，避免了对获得O J I P动力学的关键因素进行任何假设。该模型成功模拟了观察到的荧光诱导动力学，包括O J I P瞬态。此模型中的荧光发射是直接根据PSII核心和外周天线中激发单重态叶绿素的量计算得出的。电子和能量转移通过一系列联立微分方程进行模拟。MATLAB中的可变步长数值积分程序（ode15s）提供了一种计算效率高的方法来求解这些联立方程。这个完整分子系统的计算机模拟表示为测试关于控制O J I P动力学及这些点处荧光发射的潜在机制的假设提供了一个实验平台。基于该模型的模拟表明，J对应于Q(-)AQB（QA和QB分别是PSII的第一和第二醌电子受体）和Q(-)AQ(-)B的峰值浓度，I对应于Q(-)AQ(2-)B浓度增加时的第一个拐点。P峰与Q(-)AQ(2-)B和PQH2的最大浓度一致。此外，使用该模型的模拟表明，外周天线与核心天线的不同比例会导致O点处荧光发射的差异，而不影响J、I和P点处的荧光发射。QB非还原PSII中心浓度的增加会导致O点处荧光发射更高，相应地降低可变荧光与最大荧光比值（F v/F m）。
