División Biología Molecular, Facultad de Ciencias Bioquímicas y Farmacéuticas, Instituto de Biología Molecular y Celular de Rosario, Universidad Nacional de Rosario, Suipacha 531, S2002LRK, Rosario, Argentina.
Planta. 2012 Nov;236(5):1447-58. doi: 10.1007/s00425-012-1695-x. Epub 2012 Jul 5.
Ferredoxins are iron-sulfur proteins involved in various one-electron transfer pathways. Ferredoxin levels decrease under adverse environmental conditions in photosynthetic organisms. In cyanobacteria, this decline is compensated by induction of flavodoxin, an isofunctional flavoprotein. Flavodoxin is not present in higher plants, but transgenic Nicotiana tabacum lines accumulating Anabaena flavodoxin in plastids display increased tolerance to different sources of environmental stress. As the degree of tolerance correlated with flavodoxin dosage in plastids of nuclear-transformed transgenic tobacco, we prepared plants expressing even higher levels of flavodoxin by direct plastid transformation. A suite of nuclear- and chloroplast-transformed lines expressing a wide range of flavodoxin levels, from 0.3 to 10.8 μmol m(-2), did not exhibit any detectable growth phenotype relative to the wild type. In the absence of stress, the contents of both chlorophyll a and carotenoids, as well as the photosynthetic performance (photosystem II maximum efficiency, photosystem II operating efficiency, electron transport rates and carbon assimilation rates), displayed a moderate increase with flavodoxin concentrations up to 1.3-2.6 μmol flavodoxin m(-2), and then declined to wild-type levels. Stress tolerance, as estimated by the damage inflicted on exposure to the pro-oxidant methyl viologen, also exhibited a bell-shaped response, with a significant, dose-dependent increase in tolerance followed by a drop in the high-expressing lines. The results indicate that optimal photosynthetic performance and stress tolerance were observed at flavodoxin levels comparable to those of endogenous ferredoxin. Further increases in flavodoxin content become detrimental to plant fitness.
铁硫蛋白是参与各种单电子转移途径的一类蛋白质。在光合生物中，铁硫蛋白在不利的环境条件下含量会降低。在蓝藻中，这种下降通过诱导黄素蛋白（一种同工的黄素蛋白）来补偿。黄素蛋白不存在于高等植物中，但在积累了鱼腥藻黄素蛋白的转基因烟草中，其对不同来源的环境胁迫的耐受性增加。由于耐受力与核转化的转基因烟草质体中黄素蛋白的剂量相关，因此我们通过直接质体转化来制备表达更高水平黄素蛋白的植物。一系列核和叶绿体转化的表达从 0.3 到 10.8 μmol m(-2) 的广泛黄素蛋白水平的株系与野生型相比，没有表现出任何可检测的生长表型。在没有胁迫的情况下，叶绿素 a 和类胡萝卜素的含量以及光合作用性能（光系统 II 最大效率、光系统 II 运行效率、电子传递速率和碳同化速率）均随着黄素蛋白浓度的增加而适度增加，直到 1.3-2.6 μmol 黄素蛋白 m(-2)，然后下降到野生型水平。通过对促氧化剂甲基紫精暴露造成的损伤来估计的胁迫耐受性也表现出钟形响应，随着耐受性的显著、剂量依赖性增加，随后在高表达株系中下降。结果表明，在与内源性铁硫蛋白相当的黄素蛋白水平下，观察到最佳的光合作用性能和胁迫耐受性。黄素蛋白含量的进一步增加对植物适应性不利。
