Priault P, Tcherkez G, Cornic G, De Paepe R, Naik R, Ghashghaie J, Streb P
Laboratoire d'Ecologie, Systématique et Evolution, CNRS, UMR 8079, UFR IFR 87, Université Paris XI, Orsay, France.
J Exp Bot. 2006;57(12):3195-207. doi: 10.1093/jxb/erl083. Epub 2006 Aug 31.
The cytoplasmic male sterile II (CMSII) mutant lacking complex I of the mitochondrial electron transport chain has a lower photosynthetic activity but exhibits higher rates of excess electron transport than the wild type (WT) when grown at high light intensity. In order to examine the cause of the lower photosynthetic activity and to determine whether excess electrons are consumed by photorespiration, light, and intercellular CO(2), molar fraction (c(i)) response curves of carbon assimilation were measured at varying oxygen molar fractions. While oxygen is the major acceptor for excess electrons in CMSII and WT leaves, electron flux to photorespiration is favoured in the mutant as compared with the WT leaves. Isotopic mass spectrometry measurements showed that leaf internal conductance to CO(2) diffusion (g(m)) in mutant leaves was half that of WT leaves, thus decreasing the c(c) and favouring photorespiration in the mutant. The specificity factor of Rubisco did not differ significantly between both types of leaves. Furthermore, carbon assimilation as a function of electrons used for carboxylation processes/electrons used for oxygenation processes (J(C)/J(O)) and as a function of the calculated chloroplastic CO(2) molar fraction (c(c)) values was similar in WT and mutant leaves. Enhanced rates of photorespiration also explain the consumption of excess electrons in CMSII plants and agreed with potential ATP consumption. Furthermore, the lower initial Rubisco activity in CMSII as compared with WT leaves resulted from the lower c(c) in ambient air, since initial Rubisco activity on the basis of equal c(c) values was similar in WT and mutant leaves. The retarded growth and the lower photosynthetic activity of the mutant were largely overcome when plants were grown in high CO(2) concentrations, showing that limiting CO(2) supply for photosynthesis was a major cause of the lower growth rate and photosynthetic activity in CMSII.
缺乏线粒体电子传递链复合体I的细胞质雄性不育II（CMSII）突变体，其光合活性较低，但在高光强下生长时，与野生型（WT）相比，表现出更高的过量电子传递速率。为了研究光合活性较低的原因，并确定过量电子是否被光呼吸、光照和细胞间CO₂消耗，在不同氧摩尔分数下测量了碳同化的光、细胞间CO₂摩尔分数（c(i)）响应曲线。虽然氧是CMSII和WT叶片中过量电子的主要受体，但与WT叶片相比，突变体中电子流向光呼吸更受青睐。同位素质谱测量表明，突变体叶片中CO₂扩散的叶内导度（g(m)）是WT叶片的一半，从而降低了c(c)，有利于突变体中的光呼吸。两种类型叶片之间Rubisco的特异性因子没有显著差异。此外，WT和突变体叶片中，作为用于羧化过程的电子/用于氧化过程的电子（J(C)/J(O)）的函数以及作为计算的叶绿体CO₂摩尔分数（c(c)）值的函数的碳同化相似。光呼吸速率的提高也解释了CMSII植物中过量电子的消耗，并与潜在的ATP消耗一致。此外，与WT叶片相比，CMSII中较低的初始Rubisco活性是由于环境空气中较低的c(c)，因为基于相等c(c)值的初始Rubisco活性在WT和突变体叶片中相似。当植物在高CO₂浓度下生长时，突变体生长受阻和光合活性较低的情况在很大程度上得到克服，这表明光合作用中CO₂供应受限是CMSII生长速率和光合活性较低的主要原因。
