Effects of nitrate deficiency on nitrate assimilation and chlorophyll synthesis of detached apple leaves
2019
Wen, Binbin | Li, Chen | Fu, Xiling | Li, Dongmei | Li, Ling | Chen, Xiude | Wu, Hongyu | Cui, Xiaowen | Zhang, Xinhao | Shen, Hongyan | Zhang, Wenqian | Xiao, Wei | Gao, Dongsheng
Nitrogen is one of the most important nutrients for plant growth and development. Nitrate nitrogen (NO3−-N) is the main form of nitrogen taken up by plants. Understanding the effects of exogenous NO3−-N on nitrogen metabolism at the gene expression and enzyme activity levels during nitrogen assimilation and chlorophyll synthesis is important for increasing nitrogen utilization efficiency. In this study, cell morphology, NO3−-N uptake rates, the expression of key genes related to nitrogen assimilation and chlorophyll synthesis and enzyme activity in apple leaves under NO3−-N deficiency were investigated. The results showed that the cell morphology of apple leaves was irreversibly deformed due to NO3−-N deficiency. NO3−-N was absorbed slightly one day after NO3−-N deficiency treatment and effluxed after 3 days. The relative expression of genes encoding nitrogen assimilation enzymes and the activity of such enzymes decreased significantly after 1 day of NO3−-N deficiency treatment. After treatment for 14 days, gene expression was upregulated, enzyme activity was increased, and NO3−-N content was increased. NO3−-N deficiency hindered the transformation of 5-aminobilinic acid (ALA) to porphobilinogen (PBG), suggesting a possible route by which NO3−-N levels affect chlorophyll synthesis. Collectively, the results indicate that NO3−-N deficiency affects enzyme activity by altering the expression of key genes in the nitrogen assimilation pathway, thereby suppressing NO3−-N absorption and assimilation. NO3−-N deficiency inhibits the synthesis of the chlorophyll precursor PBG, thereby hindering chlorophyll synthesis.
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