Schäfer H J, Greiner S, Rausch T, Haag-Kerwer A
Botanisches Institut, Heidelberg, Germany.
FEBS Lett. 1997 Mar 10;404(2-3):216-20. doi: 10.1016/s0014-5793(97)00132-4.
Glutathione (GSH) is the precursor of the phytochelatins (PC), which in plants and fungi are involved in heavy metal sequestration. The regulatory enzyme gamma-glutamylcysteine synthetase (gamma-ECS) catalyzes the first step in GSH biosynthesis. For the heavy metal accumulator Brassica juncea L. a partial gamma-ECS cDNA was cloned by RT-PCR. Treatment of suspension-cultured dark grown seedlings with micromolar concentrations of CuSO4 resulted in a strong increase of gamma-ECS mRNA in roots and shoots, concomitant with an increase of GSH and phytochelatins. A significant up-regulation of gamma-ECS mRNA was observed at 25 microM CuSO4 (shoot growth: -11%), whereas maximum up-regulation was obtained at 100 microM CuSO4 (shoot growth: -60%). Unexpectedly, metallothionein 2 (MT2) mRNA was decreased in response to the CuSO4 treatments. CdSO4 at a concentration of 50 microM caused a 72% reduction in shoot growth without affecting the amounts of gamma-ECS- and MT2 mRNAs. ZnSO4 at a concentration of 500 microM did not reduce growth but induced transient increases of gamma-ECS- and MT2 mRNAs. The implications of the results with respect to differential regulation of gamma-ECS and MT2 during heavy metal exposure are discussed.
谷胱甘肽（GSH）是植物螯合肽（PC）的前体，在植物和真菌中，植物螯合肽参与重金属螯合作用。调节酶γ-谷氨酰半胱氨酸合成酶（γ-ECS）催化GSH生物合成的第一步。对于重金属积累植物印度芥菜，通过逆转录聚合酶链反应（RT-PCR）克隆了部分γ-ECS cDNA。用微摩尔浓度的硫酸铜处理悬浮培养的黑暗生长幼苗，导致根和芽中γ-ECS mRNA显著增加，同时GSH和植物螯合肽也增加。在25微摩尔/升硫酸铜处理时观察到γ-ECS mRNA显著上调（芽生长：-11%），而在100微摩尔/升硫酸铜处理时获得最大上调（芽生长：-60%）。出乎意料的是，金属硫蛋白2（MT2）mRNA在硫酸铜处理后减少。50微摩尔/升的硫酸镉导致芽生长减少72%，但不影响γ-ECS和MT2 mRNA的量。500微摩尔/升的硫酸锌不降低生长，但诱导γ-ECS和MT2 mRNA短暂增加。本文讨论了这些结果对于重金属暴露期间γ-ECS和MT2差异调节的意义。
