Effects of altered citrate synthase and isocitrate dehydrogenase expression on internal citrate concentrations and citrate efflux from tobacco (Nicotiana tabacum L.) roots
Effects of altered citrate synthase and isocitrate dehydrogenase expression on internal citrate concentrations and citrate efflux from tobacco (Nicotiana tabacum L.) roots
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DOI：
10.1023/a:1022352914101
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发表时间：
2003-01-01
期刊：
影响因子：
4.9
通讯作者：
Richardson, AE
中科院分区：
文献类型：
--
作者：
Delhaize, E;Ryan, PR;Richardson, AE
为了评估以增加柠檬酸从根部流出为目的的操纵柠檬酸代谢的有效性，我们生成了转基因烟草（Nicotiana tabacum L.）品系，这些品系要么过度表达线粒体柠檬酸合酶（EC 4.1.3.7）活性，要么降低胞浆异柠檬酸脱氢酶（EC 1.1.1.42）活性。尽管转基因株系中柠檬酸合酶活性增加了高达5倍，但与对照相比，内部柠檬酸浓度和柠檬酸流出均没有增加，这表明在烟草中，柠檬酸合酶活性并不直接决定柠檬酸积累和流出。与对柠檬酸流出没有影响相一致，柠檬酸合酶活性的增加并没有增强转基因品系的铝抗性。对两个转基因品系收集的初步数据显示，虽然这些活性变化与两种组织的内部柠檬酸盐浓度增加1.5倍有关，但根部的柠檬酸盐流出量并未增加。需要进一步的工作来确定内部柠檬酸盐浓度的增加是否与这些品系的铝抗性增强有关。我们的结论是，在烟草中，内部柠檬酸盐浓度和柠檬酸盐流出很大程度上对线粒体柠檬酸合酶或胞质异柠檬酸脱氢酶活性的巨大变化不敏感，并表明其他因素（例如根部运输）控制柠檬酸盐流出。
To assess the effectiveness of manipulating citrate metabolism with the aim of increasing citrate efflux from roots, we generated transgenic tobacco (Nicotiana tabacum L.) lines that either overexpressed mitochondrial citrate synthase (EC 4.1.3.7) activity or had reduced activity of cytosolic isocitrate dehydrogenase (EC 1.1.1.42). Despite increases in citrate synthase activities in transgenic lines of up to 5-fold, neither internal citrate concentrations nor citrate efflux were increased compared to controls suggesting that, in tobacco, citrate synthase activity does not directly determine citrate accumulation and efflux. Consistent with a lack of effect on citrate efflux, the increase in citrate synthase activity did not enhance the aluminium resistance of the transgenic lines. Preliminary data collected on two transgenic lines with cytosolic isocitrate dehydrogenase activities reduced to one-tenth and one third of the control for shoot and root tissues respectively, showed that while these changes in activities were associated with a 1.5-fold increase in internal citrate concentrations of both types of tissue, citrate efflux from roots was not increased. Further work is needed to establish whether the increase in internal citrate concentration is associated with enhanced aluminium resistance of these lines. We conclude that in tobacco internal citrate concentrations and citrate efflux are largely insensitive to large changes in either mitochondrial citrate synthase or cytosolic isocitrate dehydrogenase activities and suggest that other factors, such as transport out of the roots, control citrate efflux.