Kruse J, Kopriva S, Hänsch R, Krauss G-J, Mendel R-R, Rennenberg H
Institute of Forest Botany and Tree Physiology, Georges-Köhler-Allee 053/054, 79110 Freiburg, Germany.
Plant Biol (Stuttg). 2007 Sep;9(5):638-46. doi: 10.1055/s-2007-965434.
The significance of root nitrate reductase for sulfur assimilation was studied in tobacco (NICOTIANA TABACUM) plants. For this purpose, uptake, assimilation, and long-distance transport of sulfur were compared between wild-type tobacco and transformants lacking root nitrate reductase, cultivated either with nitrate or with ammonium nitrate. A recently developed empirical model of plant internal nitrogen cycling was adapted to sulfur and applied to characterise whole plant sulfur relations in wild-type tobacco and the transformant. Both transformation and nitrogen nutrition strongly affected sulfur pools and sulfur fluxes. Transformation decreased the rate of sulfate uptake in nitrate-grown plants and root sulfate and total sulfur contents in root biomass, irrespective of N nutrition. Nevertheless, glutathione levels were enhanced in the roots of transformed plants. This may be a consequence of enhanced APR activity in the leaves that also resulted in enhanced organic sulfur content in the leaves of the tranformants. The lack of nitrate reductase in the roots in the transformants caused regulatory changes in sulfur metabolism that resembled those observed under nitrogen deficiency. Nitrate nutrition reduced total sulfur content and all the major fractions analysed in the leaves, but not in the roots, compared to ammonium nitrate supply. The enhanced organic sulfur and glutathione levels in ammonium nitrate-fed plants corresponded well to elevated APR activity. But foliar sulfate contents also increased due to decreased re-allocation of sulfate into the phloem of ammonium nitrate-fed plants. Further studies will elucidate whether this decrease is achieved by downregulation of a specific sulfate transporter in vascular tissues.
在烟草（NICOTIANA TABACUM）植株中研究了根系硝酸还原酶对硫同化的意义。为此，比较了野生型烟草和缺乏根系硝酸还原酶的转基因植株之间硫的吸收、同化及长距离运输情况，这些植株分别用硝酸盐或硝酸铵培养。一个最近开发的植物体内氮循环的经验模型被应用于硫，并用于描述野生型烟草和转基因植株的全株硫关系。转化和氮营养都强烈影响硫库和硫通量。转化降低了硝酸盐培养植株中硫酸盐的吸收速率以及根生物量中根硫酸盐和总硫含量，与氮营养无关。然而，转基因植株根系中的谷胱甘肽水平有所提高。这可能是叶片中APR活性增强的结果，这也导致转基因植株叶片中有机硫含量增加。转基因植株根系中缺乏硝酸还原酶导致硫代谢的调节变化，类似于在氮缺乏条件下观察到的变化。与供应硝酸铵相比，硝酸盐营养降低了叶片中的总硫含量以及所分析的所有主要组分，但根中没有。硝酸铵喂养的植株中有机硫和谷胱甘肽水平的提高与APR活性的升高非常吻合。但由于进入硝酸铵喂养植株韧皮部的硫酸盐再分配减少，叶片中的硫酸盐含量也增加了。进一步的研究将阐明这种减少是否通过下调维管组织中特定的硫酸盐转运体来实现。
