Luxurious Nitrogen Fertilization of Two Sugar Cane Genotypes Contrasting for Lignin Composition Causes Changes in the Stem Proteome Related to Carbon, Nitrogen, and Oxidant Metabolism but Does Not Alter Lignin Content

Sugar cane is an important crop for
sugar and biofuel production.
Its lignocellulosic biomass represents a promising option as feedstock
for second-generation ethanol production. Nitrogen fertilization can
affect differently tissues and its biopolymers, including the cell-wall
polysaccharides and lignin. Lignin content and composition are the
most important factors associated with biomass recalcitrance to convert
cell-wall polysaccharides into fermentable sugars. Thus it is important
to understand the metabolic relationship between nitrogen fertilization
and lignin in this feedstock. In this study, a large-scale proteomics
approach based on GeLC–MS/MS was employed to identify and relatively
quantify proteins differently accumulated in two contrasting genotypes
for lignin composition after excessive nitrogen fertilization. From
the ∼1000 nonredundant proteins identified, 28 and 177 were
differentially accumulated in response to nitrogen from IACSP04-065
and IACSP04-627 lines, respectively. These proteins were associated
with several functional categories, including carbon metabolism, amino
acid metabolism, protein turnover, and oxidative stress. Although
nitrogen fertilization has not changed lignin content, phenolic acids
and lignin composition were changed in both species but not in the
same way. Sucrose and reducing sugars increased in plants of the genotype
IACSP04-065 receiving nitrogen.