Regulation of sulphate assimilation by glutathione in poplars (Populus tremula x P.alba) of wild type and overexpressing γ-glutamylcysteine synthetase in the cytosol
Regulation of sulphate assimilation by glutathione in poplars (Populus tremula x P.alba) of wild type and overexpressing γ-glutamylcysteine synthetase in the cytosol
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DOI：
10.1093/jxb/erh094
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发表时间：
2004-04-01
影响因子：
6.9
通讯作者：
Kopriva, S
中科院分区：
文献类型：
--
作者：
Hartmann, T;Hönicke, P;Kopriva, S
谷胱甘肽（GSH）是植物中主要的低分子量硫醇，在逆境防御和硫的转运和储存中具有不同的功能。它的合成依赖于其组成氨基酸半胱氨酸、谷氨酸和甘氨酸的供应。谷胱甘肽是硫酸盐同化途径的反馈抑制剂，而硫酸盐同化途径是半胱氨酸合成的主要来源。对转基因杨树（Populus tremulaxP）的硫酸盐同化进行了分析。γ -谷氨酰半胱氨酸合成酶（GSH合成的关键酶）过表达，并将结果与外源添加GSH的影响进行比较。虽然转基因植株叶片GSH水平提高了3-4倍，但与野生型相比，3个转基因植株的硫酸盐同化酶，即ATP硫酰化酶、腺苷5′-磷酸硫酸还原酶（APR）、亚硫酸盐还原酶、丝氨酸乙酰转移酶和o -乙酰丝氨酸（硫醇）裂解酶的活性没有受到影响。此外，这些酶的mRNA水平不受GSH水平升高的影响。相比之下，由于外源供给的谷胱甘肽含量增加导致APR活性和mRNA积累的强烈降低。这种反馈调节通过同时加入o -乙酰丝氨酸（OAS）而恢复。然而，OAS测量表明，OAS不是转基因杨树中GSH对APR缺乏反馈调节的唯一信号。
Glutathione (GSH) is the major low molecular weight thiol in plants with different functions in stress defence and the transport and storage of sulphur. Its synthesis is dependent on the supply of its constituent amino acids cysteine, glutamate, and glycine. GSH is a feedback inhibitor of the sulphate assimilation pathway, the primary source of cysteine synthesis. Sulphate assimilation has been analysed in transgenic poplars (Populus tremulaxP. alba) overexpressing gamma-glutamylcysteine synthetase, the key enzyme of GSH synthesis, and the results compared with the effects of exogenously added GSH. Although foliar GSH levels were 3-4-fold increased in the transgenic plants, the activities of enzymes of sulphate assimilation, namely ATP sulphurylase, adenosine 5'-phosphosulphate reductase (APR), sulphite reductase, serine acetyltransferase, and O-acetylserine (thiol)lyase were not affected in three transgenic lines compared with the wild type. Also the mRNA levels of these enzymes were not altered by the increased GSH levels. By contrast, an increase in GSH content due to exogenously supplied GSH resulted in a strong reduction in APR activity and mRNA accumulation. This feedback regulation was reverted by simultaneous addition of O-acetylserine (OAS). However, OAS measurements revealed that OAS cannot be the only signal responsible for the lack of feedback regulation of APR by GSH in the transgenic poplars.