Abstract
Nitrogen (N) is one of the abundant and essential elements for plant growth and development, and N deficiency (ND) affects plants at both physiological and transcriptomic levels. Neolamarckia cadamba is a fast-growing woody plant from the Rubiaceae family. However, the physiological and molecular impacts of ND on this species have not been well investigated. Here, we studied how N. cadamba responds to ND under hydroponic conditions. In a physiological aspect, ND led to a reduction in biomass, chlorophyll content, and photosynthetic capacity. ND also impaired the assimilation of N as the activities of glutamine synthetase (GS) and nitrate reductase (NR) were decreased in the root. Interestingly, the lignin content of stem increased progressively during the ND stress. The main transcription factors, the transcription factors that are important to N regulation has been found to be upregulated, including Nodule inception-like protein 7 (NLP7), TGACG motif-binding factor 1 (TGA1), basic helix-loop-helix protein 45 (BHLH45), NAM, ATAF1,2, CUC2 (NAC) transcription factor 43 (NAC43), and basic leucine zipper pattern 44 (bZIP44). The expression of N transporters, such as nitrate transporter 2.4 (NRT2.4), ammonium transporter 3 (AMT3), and amino acid transporter protein 3 (AAP3), was also upregulated. In addition, phosphorus- and calcium-related genes such as phosphate starvation response 2 (PHR2) and cyclic nucleotide-gated ion channel 15 (CNGC15) were expressed more abundantly in response to ND stress. Our results reveal the physiological and molecular mechanisms by which woody plants respond to ND.
Highlights
Nitrogen (N) is the most important inorganic nutrient in plants
In the nitrogen deficiency (ND) treatment group, fresh weight, dry weight, plant height, and root system were not significantly different from the control at the 6th day. All these physiological indicators were lower than those in the control (CK) at the 12th day, with fresh weight reduced by 11.3%, dry weight reduced by 27%, plant height reduced by 6.5%, and root length, root surface area, and root volume reduced by 21.9, 25.9, and 29.6%, respectively (Figures 1B–G)
POD was most significantly affected in roots at the 6th day and leaves at the 12th day as its content increased by 21.1 and 79.8%, respectively, while APX, on the other hand, decreased significantly in roots, by 75.2 and 59.2% at the 6th and 12th day, respectively (Figures 2A–F)
Summary
Nitrogen (N) is the most important inorganic nutrient in plants. It is a major component of proteins, nucleic acids, cofactors, and secondary metabolites. High N availability is required to ensure high productivity of crops, including woody crops such as Nitrogen Deficiency in Neolamarckia cadamba fast-growing Poplars (Mamashita et al, 2015). In natural ecosystems and agroecosystems, the availability of N is often limited, leading to abiotic plant stress—nitrogen deficiency (ND) (Martin et al, 2002). About 75% of N fertilizer is not taken up by plants and is lost to the environment, leading to an eutrophication of water bodies and an enrichment of atmospheric N oxide gases (Gutierrez, 2012). To maintain high yields and reduce N application rates, it is necessary to better understand the molecular mechanisms that regulate the morphological and physiological adaptations of crops to N effectiveness (Rennenberg et al, 2010; Miller et al, 2012)
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