DataSheet_1_Determinants of photochemical characteristics of the photosynthetic electron transport chain of maize.docx

IntroductionThe photosynthetic electron transport chain (ETC) is the bridge that links energy harvesting during the photophysical reactions at one end and energy consumption during the biochemical reactions at the other. Its functioning is thus fundamental for the proper balance between energy supply and demand in photosynthesis. Currently, there is a lack of understanding regarding how the structural properties of the ETC are affected by nutrient availability and plant developmental stages, which is a major roadblock to comprehensive modeling of photosynthesis.
MethodsRedox parameters reflect the structural controls of ETC on the photochemical reactions and electron transport. We conducted joint measurements of chlorophyll fluorescence (ChlF) and gas exchange under systematically varying environmental conditions and growth stages of maize and sampled foliar nutrient contents. We utilized the recently developed steady-state photochemical model to infer redox parameters of electron transport from these measurements.
Results and discussionWe found that the inferred values of these photochemical redox parameters varied with leaf macronutrient content. These variations may be caused either directly by these nutrients being components of protein complexes on the ETC or indirectly by their impacts on the structural integrity of the thylakoid and feedback from the biochemical reactions. Also, the redox parameters varied with plant morphology and developmental stage, reflecting seasonal changes in the structural properties of the ETC. Our findings will facilitate the parameterization and simulation of complete models of photosynthesis.

引言
光合电子传递链（photosynthetic electron transport chain，ETC）是连接两端的核心桥梁：一端衔接光物理反应中的能量捕获过程，另一端衔接生化反应中的能量消耗过程。因此其功能对于光合作用中能量供需的动态平衡至关重要。目前，学界对于养分有效性与植物发育阶段如何影响ETC的结构特性仍缺乏足够认知，这也是制约光合过程全模型构建的主要瓶颈。

方法
氧化还原参数能够反映ETC对光化学反应及电子传递过程的结构调控作用。本研究系统调控玉米的生长环境与发育阶段，同步开展叶绿素荧光（chlorophyll fluorescence，ChlF）与气体交换的联合测定，并采集叶片样品测定其养分含量。我们借助新近开发的稳态光化学模型，从上述测定数据中推导电子传递过程的氧化还原参数。

结果与讨论
研究发现，推导得到的这些光化学氧化还原参数的数值会随叶片大量养分含量发生变化。这些变化可能由两种途径导致：一是这些养分作为ETC上蛋白质复合物的组成成分直接发挥作用；二是养分通过影响类囊体（thylakoid）的结构完整性，或通过生化反应的反馈间接产生影响。此外，氧化还原参数还会随植物形态与发育阶段发生变化，反映出ETC结构特性的季节动态。本研究结果将有助于光合全模型的参数化构建与模拟工作。