The Effect of Nitrogen Fertilizer on Rhizome Quality and Starch Physicochemical Properties in Nelumbo nucifera

Abstract

Optimal nitrogen (N) supply significantly increases the starch content, components, and yield of Nelumbo nucifera. However, the underlying transcriptional mechanism and starch accumulation under dose-dependent nitrogen fertilizer are poorly understood. In this study, we found that the optimal nitrogen fertilizer (N2, 30 kg/667 m2) was more beneficial to improve the stomatal conductance (Gs), leaf intercellular CO2 concentration (Ci), transpiration rate (Tr), net photosynthetic rates (Pn), chlorophyll content, starch content, and plot yield. What is more, N2-fertilizer treatment induced a higher number of starch granule, AP2 content, and RVA curve peaks. Then, the transcriptomic analyses performed in control (CK) and N2-fertilizer treatment (N2) showed that the expressions of many differentially expressed genes (DEGs) were significantly induced by N2. KEGG and GO enrichment analysis showed that these DEGs were significantly enriched in biosynthesis of secondary metabolites, phenylpropanoid biosynthesis, carbon metabolism, carbon fixation in photosynthetic organisms, plant hormone signal transduction, and starch and sucrose metabolisms, suggesting that nitrogen fertilizer induced alterations of photosynthesis- and starch accumulation-related gene expression profiles. Finally, six photosynthesis-related genes and fourteen starch synthesis-related genes were confirmed to be required for starch accumulation in the Nelumbo nucifera development. qPCR analysis of six starch accumulation-related genes demonstrated the accuracy of the transcriptome. Hence, our study provides valuable resource for future studies on molecular mechanisms underlying starch accumulation in Nelumbo nucifera rhizome under N-fertilizer treatment.

Integrated mRNA and Small RNA Sequencing Reveals a microRNA Regulatory Network Associated with Starch Biosynthesis in Lotus (Nelumbo nucifera Gaertn.) Rhizomes

“…In our study, the content of amylose, the content of amylopectin, and the content of starch all had an upward trend from Z6-1 to Z6-3, which showed that the first internode is in the vigorous period of starch development, while the third internode has been preliminarily completed. This is consistent with the rising trend of amylose content, amylopectin content and starch content from the beginning stage to the end stage [5,32].…”

“…The content of amylose, amylopectin, and starch had significant difference in three internodes of lotus rhizome, which had upward trend from Z6-1 to Z6-3 ( Figure 1 A). In paraffin section observation, there existed two types of granules, long oval starch granules and round starch granules, which may indicate the ratio of amylose and amylopectin [ 5 ]. The results of statistics of two forms of starch granules showed that the number of long oval starch granules, round starch granules and total starch granules were highest in Z6-1, second in Z6-2 and lowest in Z6-3 ( Figure 1 B,C), which were consistent with those of starch determination.…”

“…During the development of lotus, most of the genes related to starch synthesis are expressed actively. [ 5 , 32 ]. SUS and SS were involved in the changes at development stages of lotus rhizome [ 26 ].…”

“…Fresh lotus rhizome and its processed products are not only resistant to storage and transportation, but also rich in nutrients such as starch, protein, vitamins, flavonoid, and mineral substances, and is famous for its nutritional and medicinal values, which are deeply loved by consumers at home and abroad [ 3 , 4 ]. According to Compendium of Materia written by Shizhen Li, “The lotus decocted with water could detoxify fungus poison and prevent blood collapse and blood drowning.” [ 5 ]. The starch content accounting for more than 70% of the total dry rhizome matter is the main factor affecting lotus rhizome edible quality [ 6 ].…”

“…According to Compendium of Materia written by Shizhen Li, "The lotus decocted with water could detoxify fungus poison and prevent blood collapse and blood drowning." [5]. The starch content accounting for more than 70% of the total dry rhizome matter is the main factor affecting lotus rhizome edible quality [6].…”