Kopriva Stanislav, Rennenberg Heinz
Albert-Ludwigs-University of Freiburg, Institute of Forest Botany and Tree Physiology, Georges-Köhler-Allee 053, D-79110 Freiburg, Germany.
J Exp Bot. 2004 Aug;55(404):1831-42. doi: 10.1093/jxb/erh203. Epub 2004 Jul 30.
Sulphate assimilation is an essential pathway being a source of reduced sulphur for various cellular processes and for the synthesis of glutathione, a major factor in plant stress defence. Many reports have shown that sulphate assimilation is well co-ordinated with the assimilation of nitrate and carbon. It has long been known that, during nitrate deficiency, sulphate assimilation is reduced and that the capacity to reduce nitrate is diminished in plants starved for sulphate. Only recently, however, was it shown that adenosine 5' phosphosulphate reductase (APR), the key enzyme of sulphate assimilation, is regulated by carbohydrates. In plants treated with sucrose or glucose APR was induced, whereas the activity was strongly reduced in plants grown in CO(2)-free air. The availability of cysteine is a crucial factor in glutathione synthesis, but an adequate supply of glutamate and glycine are also important. The molecular mechanisms for the co-ordination of S, N, and C assimilation are not known. O-acetylserine, a precursor of cysteine, was proposed to be the signal regulating sulphate assimilation, but most probably is not the outgoing signal to N and C metabolism. cDNA arrays revealed the induction of genes involved in auxin synthesis upon S-starvation, pointing to a possible role of phytohormones. Clearly, despite significant progress in understanding the regulation of sulphate assimilation and glutathione synthesis, their co-ordination with N and C metabolism achieved, and several potential signal molecules identified, present knowledge is still far from being sufficient.
硫酸盐同化是一条必不可少的途径，它为各种细胞过程提供还原态硫，并用于合成谷胱甘肽，而谷胱甘肽是植物应激防御中的一个主要因素。许多报告表明，硫酸盐同化与硝酸盐和碳的同化密切协调。长期以来人们都知道，在硝酸盐缺乏期间，硫酸盐同化会减少，而在缺乏硫酸盐的植物中，硝酸盐还原能力也会降低。然而，直到最近才发现，硫酸盐同化的关键酶——腺苷5'-磷酸硫酸还原酶（APR）受碳水化合物调控。在用蔗糖或葡萄糖处理的植物中，APR被诱导，而在无CO₂空气中生长的植物中，其活性则大幅降低。半胱氨酸的可用性是谷胱甘肽合成中的一个关键因素，但充足的谷氨酸和甘氨酸供应也很重要。S、N和C同化协调的分子机制尚不清楚。半胱氨酸的前体O-乙酰丝氨酸被认为是调节硫酸盐同化的信号，但很可能不是向N和C代谢传递的信号。cDNA阵列显示，S饥饿时生长素合成相关基因被诱导，这表明植物激素可能发挥作用。显然，尽管在理解硫酸盐同化和谷胱甘肽合成的调控方面取得了重大进展，实现了它们与N和C代谢的协调，并鉴定出了几种潜在的信号分子，但目前的知识仍远远不够。
