Dai Ziyu, Ku Maurice S B, Edwards Gerald E
Department of Botany, Washington State University, 99164-4238, Pullman, WA, USA.
Planta. 1996 Apr;198(4):563-571. doi: 10.1007/BF00262643. Epub 2017 Mar 18.
Two major indicators were used to access the degree of photorespiration in various photosynthetic types of Flaveria species (C, C-C, C-like, and C): the O inhibition of photosynthesis measured above the O partial pressure which gives a maximum rate, and O- and light-dependent whole-chain electron flow measured at the CO compensation point (Γ). The optimum level of O for maximum photosynthetic rates under atmospheric levels of CO (34 Pa) was lower in C and C-C species (ca. 2 kPa) than in C-like and C species (ca. 9 kPa). Increasing O partial pressures from the optimum for photosynthesis up to normal atmospheric levels (ca. 20 kPa) caused an inhibition of photosynthesis which was more severe under lower CO. This inhibition was calculated as the O inhibition index (Θ, the percentage inhibition of photosynthesis per kPa increase in O). From measurements of 18 Flaveria species at atmospheric CO, the Θ values decreased from C (1.9-2.1) to C-C (1.2-1.6), C-like (0.6-0.8) and C species (0.3-0.4), indicating a progressive decrease in apparent photorespiration in this series. With increasing irradiance at Γ under atmospheric levels of O, and increasing O partial pressure at 300 μmol quanta·m·s, there was a similar increase in the rate of O evolution associated with whole-chain electron flow (J, calculated from chlorophyll fluorescence analysis) in the C and C-C species compared to a much lower rate in the C-like and C species. The results indicate that there is substantial O-dependent electron flow in C and C-C species, reflecting a high level of photorespiration compared to that in C-like and C species. Consistent with these results, there was a significant decrease in Γ from C (6-6.2 Pa) to C-C (1.0-3.0 Pa), to C-like and C species (0.3-0.8 Pa), indicating a progressive decrease in apparent photorespiration. However, C and C-C species examined had high intrinsic levels of photorespiration with the latter maintaining low apparent rates of photorespiration and lower Γ values, primarily by refixing photorespired CO. The C-like and C Flaveria species had low, but measurable, levels of photorespiration via selective localization of ribulose-1,5-bisphosphate carboxylase in bundle sheath cells and operation of a CO pump via the C pathway.
使用两个主要指标来评估不同光合类型的黄顶菊属植物（C₃、C₃ - C₄中间型、C₄ - 类植物和C₄）的光呼吸程度：在能产生最大光合速率的氧分压之上测量的光合作用对氧的抑制，以及在二氧化碳补偿点（Γ）处测量的依赖氧和光的全链电子流。在大气二氧化碳水平（34帕）下，C₃和C₃ - C₄中间型物种达到最大光合速率时的最佳氧水平（约2千帕）低于C₄ - 类植物和C₄物种（约9千帕）。将氧分压从光合作用的最佳值提高到正常大气水平（约20千帕）会导致光合作用受到抑制，在较低二氧化碳水平下这种抑制更严重。这种抑制被计算为氧抑制指数（Θ，即氧分压每增加1千帕时光合作用的抑制百分比）。在大气二氧化碳条件下对18种黄顶菊属植物进行测量，Θ值从C₃（1.9 - 2.1）降至C₃ - C₄中间型（1.2 - 1.6）、C₄ - 类植物（0.6 - 0.8）和C₄物种（0.3 - 0.4），表明该系列中表观光呼吸逐渐降低。在大气氧水平下，随着在Γ处辐照度增加，以及在300微摩尔量子·米⁻²·秒⁻¹时氧分压增加，与全链电子流相关的氧释放速率（J，表示为从叶绿素荧光分析计算得出）在C₃和C₃ - C₄中间型物种中增加，而在C₄ - 类植物和C₄物种中增加幅度小得多。结果表明，C₃和C₃ - C₄中间型物种中存在大量依赖氧的电子流，这反映出与C₄ - 类植物和C₄物种相比，它们具有较高水平的光呼吸。与这些结果一致，从C₃（6 - 6.2帕）到C₃ - C₄中间型（1.0 - 3.0帕），再到C₄ - 类植物和C₄物种（0.3 - 0.8帕），Γ值显著降低，表明表观光呼吸逐渐降低。然而，所研究的C₃和C₃ - C₄中间型物种具有较高的光呼吸内在水平，后者主要通过重新固定光呼吸产生的二氧化碳来维持较低的表观光呼吸速率和较低的Γ值。C₄ - 类植物和C₄黄顶菊属物种通过将1,5 - 二磷酸核酮糖羧化酶选择性地定位在维管束鞘细胞中，并通过C₄途径运行二氧化碳泵，具有较低但可测量的光呼吸水平。
