Formation of unidentified nitrogen in plants: an implication for a novel nitrogen metabolism
Formation of unidentified nitrogen in plants: an implication for a novel nitrogen metabolism
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DOI：
10.1007/s00425-003-1200-7
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发表时间：
2004-05-01
期刊：
影响因子：
4.3
通讯作者：
Suzuki, H
中科院分区：
文献类型：
--
作者：
Morikawa, H;Takahashi, M;Suzuki, H
植物吸收无机氮并将其储存不变或将其转化为有机形式。这种有机化合物中的氮可通过凯氏定氮法按化学计量回收。无机氮和凯氏氮的总和早已被认为等于植物中的总氮。然而，在我们试图研究二氧化氮（NO2）代谢机制的过程中，我们意外地发现，拟南芥（Arabidopsis thaliana（L.））吸收的来自N-15标记NO2的总氮中，约有三分之一来自N-15标记NO2。嘿植物既不转化为无机氮也不转化为凯氏氮，而是转化为一种迄今未知的氮化合物。我们在此将这种氮称为未鉴定氮（UN）。不同物种、不同氮源、不同栽培环境下UN形成的一般规律如下。首先，所有其他11种植物研究被发现形成UN响应（NO2）-N-15熏蒸。其次是烟草（Nicotiana tabacum L.）用N-15-硝酸盐喂养的植物似乎形成了UN。最后，自然生长的蔬菜、草和路边树木的叶子被发现拥有联合国。此外，UN似乎包括这些植物物种中总氮的相当大的比例。总的来说，我们目前的研究结果表明，有一个新的氮在植物中形成UN的机制。基于凯氏定氮法消化含UN植物样品的废气和残渣馏分的分析，推断出可能的候选化合物，承担UN是那些含有热不稳定的氮-氧功能和那些不受凯氏定氮法消化，包括有机硝基和亚硝基化合物。我们建议UN轴承化合物可能提供了一个化学基础的机制，活性氮物种（RNS），因此，在植物中UN和RNS代谢之间可能会发生串扰。提出了一种以RNS为中间体的UN轴承化合物的形成机理。这种新的氮代谢的重要的广泛影响，不仅对植物的一般生理，而且对植物物质作为人类和动物的食物，并对植物作为全球环境的一个组成部分，进行了讨论。
Plants take up inorganic nitrogen and store it unchanged or convert it to organic forms. The nitrogen in such organic compounds is stoichiometrically recoverable by the Kjeldahl method. The sum of inorganic nitrogen and Kjeldahl nitrogen has long been known to equal the total nitrogen in plants. However, in our attempt to study the mechanism of nitrogen dioxide (NO2) metabolism, we unexpectedly discovered that about one-third of the total nitrogen derived from N-15-labeled NO2 taken up by Arabidopsis thaliana (L.) Heynh. plants was converted to neither inorganic nor Kjeldahl nitrogen, but instead to an as yet unknown nitrogen compound(s). We here refer to this nitrogen as unidentified nitrogen (UN). The generality of the formation of UN across species, nitrogen sources and cultivation environments for plants has been shown as follows. Firstly, all of the other 11 plant species studied were found to form the UN in response to fumigation with (NO2)-N-15. Secondly, tobacco (Nicotiana tabacum L.) plants fed with N-15-nitrate appeared to form the UN. And lastly, the leaves of naturally fed vegetables, grass and roadside trees were found to possess the UN. In addition, the UN appeared to comprise a substantial proportion of total nitrogen in these plant species. Collectively, all of our present findings imply that there is a novel nitrogen mechanism for the formation of UN in plants. Based on the analyses of the exhaust gas and residue fractions of the Kjeldahl digestion of a plant sample containing the UN, probable candidates for compounds that bear the UN were deduced to be those containing the heat-labile nitrogen-oxygen functions and those recalcitrant to Kjeldahl digestion, including organic nitro and nitroso compounds. We propose UN-bearing compounds may provide a chemical basis for the mechanism of the reactive nitrogen species (RNS), and thus that cross-talk may occur between UN and RNS metabolisms in plants. A mechanism for the formation of UN-bearing compounds, in which RNS are involved as intermediates, is proposed. The important broad impact of this novel nitrogen metabolism, not only on the general physiology of plants, but also on plant substances as human and animal food, and on plants as an integral part of the global environment, is discussed.