Abstract
Nitrogen (N) is a major component of the photosynthetic apparatus and is widely used as a fertilizer in crops. However, to the best of our knowledge, the dynamic of photosynthesis establishment due to differential N supply in the bioenergy crop sugarcane has not been reported to date. To address this question, we evaluated physiological and metabolic alterations along the sugarcane leaf in two contrasting genotypes, responsive (R) and nonresponsive (NR), grown under high- and low-N conditions. We found that the N supply and the responsiveness of the genotype determined the degree of senescence, the carboxylation process mediated by phosphoenolpyruvate carboxylase (PEPcase) and differential accumulation of soluble sugars. The metabolite profiles indicated that the NR genotype had a higher respiration rate in the youngest tissues after exposure to high N. We observed elevated levels of metabolites related to photosynthesis in almost all leaf segments from the R genotype under high-N conditions, suggesting that N supply and the ability to respond to N influenced photosynthesis. Therefore, we observed that N influence on photosynthesis and other pathways is dependent on the genotype and the leaf region.
Highlights
Sugarcane (Saccharum spp L.) is considered to be a renewable feedstock for economically valuable products, such as sugar and bioethanol[1,2]
Considering that grass leaves have a well-defined developmental gradient with a cell division zone at the base followed by cell elongation and maturation zones[32,33,34], the use of metabolic profiling can be helpful for understanding the C4 photosynthesis establishment process and leaf development
According to principal component analysis (PCA) of 17 traits, in the 10 N treatment (10 mg of N per kg of sand), the two genotypes were grouped into a single cluster (Supplementary Fig. S6), indicating that both had a similar response to low-N conditions
Summary
Sugarcane (Saccharum spp L.) is considered to be a renewable feedstock for economically valuable products, such as sugar and bioethanol[1,2]. The photosynthetic proteins of plastids are extensively degraded in an early phase of senescence compared to other proteins[24,25] For both annual and perennial plants, this process contributes to N remobilization from senescent leaves to growing organs and seeds[26,27]. Despite the dearth of studies on leaf senescence process in sugarcane, one study[28] observed that N, P, and K had higher levels of remobilization than did B, Cu, Fe and Zn, between different leaves and in different regions of the same leaf (base, middle and tip). Another study compared the metabolic profile of different segments of maize and rice leaves and observed that C3 and C4 species have specific metabolite signatures concerning amino acids levels and other organic acids involved in photosynthesis[35]. There have been relatively few studies using metabolomics to assess sucrose accumulation[31], stem development[30] and genotypic characterization[37]
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