Yang Huayiu, Menz Jochen, Häussermann Iris, Benz Martin, Fujiwara Toru, Ludewig Uwe
Institute of Crop Science, Nutritional Crop Physiology, University of Hohenheim, Fruwirthstr. 20, D-70593 Stuttgart, Germany.
The University of Tokyo Yayoi, Bunkyo-ku, Tokyo, 113-8657 Japan.
Plant Cell Physiol. 2015 Aug;56(8):1588-97. doi: 10.1093/pcp/pcv067. Epub 2015 May 7.
Urea is the most widespread nitrogen (N) fertilizer worldwide and is rapidly degraded in soil to ammonium by urease. Ammonium is either taken up by plant roots or is further processed to nitrate by soil microorganisms. However, urea can be taken up by roots and is further degraded to ammonium by plant urease for assimilation. When urea is supplied under sterile conditions, it acts as a poor N source for seedlings or adult Arabidopsis thaliana plants. Here, the gene expression of young seedlings exposed to urea and ammonium nitrate nutrition was compared. Several primary metabolism and transport genes, including those for nitrate and urea, were differentially expressed in seedlings. However, urease and most major intrinsic proteins were not differentially expressed, with the exception of NIP6;1, a urea-permeable channel, which was repressed. Furthermore, little overlap with the gene expression with ammonium as the sole N source was observed, confirming that pure urea nutrition is not associated with the ammonium toxicity syndrome in seedlings. The direct root uptake of urea was increased under boron deficiency, in both the high and low affinity range. This activity was entirely mediated by the NIP5;1 channel, which was confirmed to transport urea when expressed in oocytes. The uptake of urea in the high and low affinity range was also determined for maize and wheat roots. The urea uptake by maize roots was only about half that of wheat, but was not stimulated by boron deficiency or N deficiency in either species. This analysis identifies novel components of the urea uptake systems in plants, which may become agronomically relevant to urea uptake and utilization, as stabilized urea fertilizers become increasingly popular.
尿素是全球使用最为广泛的氮肥，在土壤中会被脲酶迅速降解为铵态氮。铵态氮要么被植物根系吸收，要么被土壤微生物进一步转化为硝态氮。然而，尿素也能被根系吸收，并被植物脲酶进一步降解为铵态氮以供同化。在无菌条件下供应尿素时，它对拟南芥幼苗或成株来说是一种较差的氮源。在此，对处于尿素和硝酸铵营养条件下的幼苗的基因表达进行了比较。包括硝酸盐和尿素相关基因在内的几个初级代谢和转运基因在幼苗中差异表达。然而，脲酶和大多数主要内在蛋白没有差异表达，但尿素通透通道NIP6;1除外，它受到了抑制。此外，几乎没有观察到与以铵态氮作为唯一氮源时的基因表达有重叠，这证实了纯尿素营养与幼苗中的铵中毒综合征无关。在硼缺乏条件下，无论在高亲和力还是低亲和力范围内，根系对尿素的直接吸收都有所增加。这种活性完全由NIP5;1通道介导，该通道在卵母细胞中表达时被证实可转运尿素。还测定了玉米和小麦根系在高亲和力和低亲和力范围内对尿素的吸收情况。玉米根系对尿素的吸收量仅约为小麦的一半，但在这两个物种中，硼缺乏或氮缺乏均未刺激其对尿素的吸收。该分析确定了植物尿素吸收系统的新成分，随着稳定性尿素肥料越来越受欢迎，这些成分可能在农学上与尿素的吸收和利用相关。
