The contribution of N remobilization is crucial for new shoots growth and quality formation during spring tea shoots development. However, the translocation mechanism of N from source leaves to sink young shoots is not well understood. In the present study, ¹⁵N urea was applied to mature tea leaves one week before bud break to track N remobilization in a field experiment. The dynamic changes in plant ¹⁵N abundance, contents of amino acids, and the expression levels of genes related to N metabolism and translocation were followed during the 18‐d development of new spring shoots until three expanding young leaves. The results showed that during the growth of new shoots the amount of ¹⁵N in the shoots increased, whereas the N_dff (N derived from ¹⁵N‐urea) in mature leaves decreased, showing that the foliar‐applied N in mature leaves was readily exported to new shoots. This process was found to be accompanied by decline of chlorophylls. In the mature leaves, expression CsATG18a and CsSAG12 involved in autophagy was dramatically induced (> 4‐fold) at approximately nine days after the bud breaking. The genes involved in the transformation of amino acids, including primarily CsGDH2, CsGDH4, CsGLT3, CsGS1;3, and CsASN2 were upregulated by > 3‐fold after bud breaking. The expression levels of CsATG8A, CsATG9, CsSAG12, CsGS1;1, CsGDH1, and CsAAP6 correlated negatively with the N_dff in mature leaves, but positively with ¹⁵N amount and total N amount in new shoots, suggesting these genes played important roles in N export from mature leaves. In the new shoots, the expression of most genes showed two defined peaks, one on six days and one on 12 days after bud breaking. The expression of CsGS2, CsASN3, CsGLT1, and CsAAP4 positively correlated with the ¹⁵N amount and total N amount in new shoots. These genes might be involved in the transport and re‐assimilation of N from mature leaves. The overall results demonstrated that the translocation of ¹⁵N from mature leaves to new spring shoots was regulated by the genes involved in autophagy, protein degradation, amino acid transformation and transport.

中文翻译：

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茶树春梢发育过程中叶片从氮到新芽的氮转运动态及相关基因表达

氮素迁移的贡献对于新芽生长和春季茶芽发育过程中的品质形成至关重要。然而，人们对氮从源叶到下沉幼芽的易位机制还没有很好的了解。在本研究中，在田间试验前的一周内，将¹⁵ N尿素应用于成熟茶叶，以追踪N的迁移。在春季新芽的第18天发育过程中，跟踪植物¹⁵ N含量，氨基酸含量以及与N代谢和易位相关的基因的表达水平的动态变化，直到三片膨胀的幼叶。结果表明，在新芽生长过程中，芽中¹⁵ N的含量增加，而N _dff成熟叶片中的氮（来自¹⁵ N-尿素的氮）减少，表明成熟叶片中叶面施用的氮很容易输出到新芽上。发现该过程伴随着叶绿素的下降。在成熟的叶子中，芽破裂后约九天，可显着诱导自噬中涉及的表达CsATG18a和CsSAG12（> 4倍）。芽断裂后，参与氨基酸转化的基因主要包括CsGDH2，CsGDH4，CsGLT3，CsGS1; 3和CsASN2。CsATG8A，CsATG9，CsSAG12，CsGS1; 1，CsGDH1和CsAAP6的表达水平与N呈负相关_dff在成熟叶片中，但正向显示为¹⁵ N和新芽中的总N量，表明这些基因在成熟叶片的N出口中起重要作用。在新芽中，大多数基因的表达表现出两个确定的峰，一个在芽断裂后六天，另一个在十二天后。的表达CsGS2，CsASN3，CsGLT1和CsAAP4与正相关¹⁵在新芽氮量和总氮量。这些基因可能参与了成熟叶片中氮的转运和重新同化。总体结果表明，易位¹⁵从成熟叶片到新芽的氮素受自噬，蛋白质降解，氨基酸转化和转运相关基因的调控。