Ammonium nitrogen and nitrate nitrogen are the two main sources of inorganic nitrogen in plants, but excess ammonium nitrogen has a toxic effect on plant cells. This characteristic of ammonium nitrogen is considered to be an important limiting factor for plants to efficiently utilize ammonium nitrogen. However, people's understanding of the plant ammonium poisoning mechanism is still very preliminary. With the development of molecular biology technology, a number of international research groups have discussed the molecular mechanism of plant ammonium toxicity. Currently, about 10 related papers have been published in the international plant biology top journal.
The research team of Shi Weiming, a researcher from the Nanjing Institute of Soil Science, Chinese Academy of Sciences, took the lead in applying the model plant Arabidopsis thaliana to study the molecular response mechanism of plant ammonium poisoning. A series of progress. Related results have been published in "Journal of Soil Science" (Li Baohai and Shi Weiming, 2007, 44: 508), Plant Cell and Environment (Li et al., 2010, 33: 1529; Li et al., 2011, 34, 933; IF = 5.2, Plant Science Zone I), Journal of Experimental Botany (Zou et al., 2012, 63: 3777; IF = 5.3, Plant Science Zone II), Planta (Li et al., 2012, 235: 239; IF = 3 , District 2 of Plant Science).
Recently, the team has made important progress in the gene expression regulation mechanism of plants responding to ammonium, and the relevant results have been published online in Plant Physiology (Li et al., 2012, doi: IF = 6.5), a journal of the first area of ​​plant science. This study used positive genetics, genomics, bioinformatics, and physiology to screen for a highly sensitive mutant amos1 material that responded to ammonium yellowing in the higher concentration range of ammonium that normally behaves in wild-type Arabidopsis. , Gene map cloning and complementary verification amos1 is a new allelic mutation of plastid metalloproteinase EGY1. Genome-wide nuclear gene transcription analysis revealed that a large number of genes responsive to ammonium stress decreased significantly in amos1 mutants, indicating that plastid AMOS1 / EGY1 is a key factor regulating the expression of ammonium stress-responsive genes. This also shows that there is a plastid feedback regulation signal pathway to regulate the expression of ammonium stress response genes.
In-depth analysis of AMOS1 / EGY1-dependent ammonium-responsive promoter sequence regulatory elements of all up-regulated genes found that 63% of the genes contained ACGTG sequences in the promoter region, which is the core sequence of the plant hormone abscisic acid (ABA) signal. This implies that ABA signal is likely to participate in the AMOS1 / EGY1-dependent plastid feedback signal regulation pathway. Further pharmacological, transcriptomics and genetics results prove that ABA signaling is an important but not the only downstream signaling pathway for AMOS1 / EGY1-dependent plastid feedback signaling.
The study further explored the upstream signal in the plastid feedback signaling pathway dependent on AMOS1 / EGY1 and found that reactive oxygen species (ROS) in the plastid is a potential plastid signaling substance. Therefore, this study not only found a key gene regulating ammonium response, but also systematically revealed its related signal pathways. After the article was published online, he was invited by the editor of Plant Signal and Behavior to write a related review.
In the above study, an interesting phenomenon was found. Compared with hyperammonium in roots, exposure of hyperammonium in leaves is more likely to inhibit lateral root formation, resulting in yellowing of the leaves. This shows that the leaves of plants are relatively sensitive areas of ammonium. This mechanism also explains the reason why plant ammonium poisoning occurs more in the seedling stage in actual agricultural production. For example, excessive urea causes the phenomenon of "burning seedlings", which may be due to the easy exposure of the leaves of the seedlings to excessive ammonium nitrogen in the soil. Poisoning. The above research results have certain reference value for reasonable application of foliar fertilizer, seed fertilizer and nitrogen fertilizer at seedling stage.
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