Department of Metabolic Biology, John Innes Centre, Norwich NR4 7UH, UK.
Plant J. 2011 Jan;65(1):96-105. doi: 10.1111/j.1365-313X.2010.04410.x. Epub 2010 Nov 22.
Sulfur is an essential nutrient for all organisms. Plants take up most sulfur as inorganic sulfate, reduce it and incorporate it into cysteine during primary sulfate assimilation. However, some of the sulfate is partitioned into the secondary metabolism to synthesize a variety of sulfated compounds. The two pathways of sulfate utilization branch after activation of sulfate to adenosine 5'-phosphosulfate (APS). Recently we showed that the enzyme APS kinase limits the availability of activated sulfate for the synthesis of sulfated secondary compounds in Arabidopsis. To further dissect the control of sulfur partitioning between the primary and secondary metabolism, we analysed plants in which activities of enzymes that use APS as a substrate were increased or reduced. Reduction in APS kinase activity led to reduced levels of glucosinolates as a major class of sulfated secondary metabolites and an increased concentration of thiols, products of primary reduction. However, over-expression of this gene does not affect the levels of glucosinolates. Over-expression of APS reductase had no effect on glucosinolate levels but did increase thiol levels, but neither glucosinolate nor thiol levels were affected in mutants lacking the APR2 isoform of this enzyme. Measuring the flux through sulfate assimilation using [(35) S]sulfate confirmed the larger flow of sulfur to primary assimilation when APS kinase activity was reduced. Thus, at least in Arabidopsis, the interplay between APS reductase and APS kinase is important for sulfur partitioning between the primary and secondary metabolism.
硫是所有生物体必需的营养物质。植物主要以无机硫酸盐的形式吸收大部分硫，在初级硫酸盐同化过程中还原并将其掺入半胱氨酸。然而，一部分硫酸盐被分配到次级代谢中，用于合成各种硫酸化化合物。硫酸盐利用的两条途径在硫酸盐激活为腺苷 5'-磷酸硫酸盐（APS）后分支。最近，我们表明 APS 激酶限制了激活硫酸盐用于合成拟南芥中硫酸化次级化合物的可用性。为了进一步剖析初级和次级代谢之间的硫分配控制，我们分析了增加或减少使用 APS 作为底物的酶活性的植物。APS 激酶活性的降低导致主要的硫酸化次级代谢产物之一——芥子油苷的水平降低，而初级还原产物——硫醇的浓度增加。然而，该基因的过表达并不影响芥子油苷的水平。APS 还原酶的过表达对芥子油苷水平没有影响，但确实增加了硫醇水平，但缺乏该酶的 APR2 同工型的突变体中既不受芥子油苷也不受硫醇水平的影响。使用 [(35) S]硫酸盐测量硫酸盐同化的通量证实，当 APS 激酶活性降低时，硫更多地流向初级同化。因此，至少在拟南芥中，APS 还原酶和 APS 激酶之间的相互作用对于初级和次级代谢之间的硫分配很重要。
