Topochemical distribution of lignin and hydroxycinnamic acids in sugar-cane cell walls and its correlation with the enzymatic hydrolysis of polysaccharides

Abstract

BackgroundLignin and hemicelluloses are the major components limiting enzyme infiltration into cell walls. Determination of the topochemical distribution of lignin and aromatics in sugar cane might provide important data on the recalcitrance of specific cells. We used cellular ultraviolet (UV) microspectrophotometry (UMSP) to topochemically detect lignin and hydroxycinnamic acids in individual fiber, vessel and parenchyma cell walls of untreated and chlorite-treated sugar cane. Internodes, presenting typical vascular bundles and sucrose-storing parenchyma cells, were divided into rind and pith fractions.ResultsVascular bundles were more abundant in the rind, whereas parenchyma cells predominated in the pith region. UV measurements of untreated fiber cell walls gave absorbance spectra typical of grass lignin, with a band at 278 nm and a pronounced shoulder at 315 nm, assigned to the presence of hydroxycinnamic acids linked to lignin and/or to arabino-methylglucurono-xylans. The cell walls of vessels had the highest level of lignification, followed by those of fibers and parenchyma. Pith parenchyma cell walls were characterized by very low absorbance values at 278 nm; however, a distinct peak at 315 nm indicated that pith parenchyma cells are not extensively lignified, but contain significant amounts of hydroxycinnamic acids. Cellular UV image profiles scanned with an absorbance intensity maximum of 278 nm identified the pattern of lignin distribution in the individual cell walls, with the highest concentration occurring in the middle lamella and cell corners. Chlorite treatment caused a rapid removal of hydroxycinnamic acids from parenchyma cell walls, whereas the thicker fiber cell walls were delignified only after a long treatment duration (4 hours). Untreated pith samples were promptly hydrolyzed by cellulases, reaching 63% of cellulose conversion after 72 hours of hydrolysis, whereas untreated rind samples achieved only 20% hydrolyzation.ConclusionThe low recalcitrance of pith cells correlated with the low UV-absorbance values seen in parenchyma cells. Chlorite treatment of pith cells did not enhance cellulose conversion. By contrast, application of the same treatment to rind cells led to significant removal of hydroxycinnamic acids and lignin, resulting in marked enhancement of cellulose conversion by cellulases.

Lignification in Sugarcane: Biochemical Characterization, Gene Discovery, and Expression Analysis in Two Genotypes Contrasting for Lignin Content

“…These authors suggested that, compared with the rind, a less lignified pith would favor cell wall degradability by increasing the accessible and potentially degradable area. Similarly, Siqueira et al (2011) observed that sugarcane pith samples were promptly hydrolyzed by cellulases, while the conversion of cellulose in rind samples was dependent on chlorite pretreatments. The significantly higher cell wall recalcitrance of sugarcane rind samples was mainly attributed to the massive presence of lignin-rich fibers and vessels, but the presence of a more condensed G-rich lignin in this anatomical region (this study) of the stem might also be implicated.…”

Ultra-Structural Mapping of Sugarcane Bagasse After Oxalic Acid Fiber Expansion (OAFEX) and Ethanol Production by Candida Shehatae and Saccharomyces Cerevisiae

“…However, visual characterizations of cellular components elucidating the hemicellulose degradation and delocalization of lignin after oxalic acid fiber expansion (OAFEX) pretreatment have yet to be performed. Cell wall anatomy of SB and macroscopic/microscopic barriers for cellulase-mediated saccharification reveal that cell wall hydrolysis encompasses several orders of magnitude (10 0 -10 -9 meters [9,10]. Oxalic acid (OA) is a strong dicarboxylic acid with higher catalytic efficiency than the sulfuric acid, and acts primarily upon hemicellulose.…”

Efeito da lignina de bagaços de cana-de-açúcar pré-tratados na hidrólise enzimática da celulose

“…Essa região é composta principalmente por feixes vasculares, formados por vasos (xilema e floema), circundados por fibras. Os feixes vasculares transportam seiva e são responsáveis pela sustentação (MOORE, 1987 Além disso, as células do córtex são mais lignificadas que as células de medula (SIQUEIRA et al, 2011;ZENG et al, 2012). Como consequência dessa maior lignificação, as células de córtex são mais recalcitrantes, oferecendo maior resistência à desconstrução enzimática, discutida mais adiante.…”

“…Além desses substituintes, grupos acetila e ácidos hidroxicinâmicos (ferúlico e cumárico) também são encontrados (WENDE; FRY, 1997). (LEE et al, 2009;SIQUEIRA et al, 2011SIQUEIRA et al, , 2013 (KANG et al, 2013;SANTOS et al, 2011;TOQUERO;BOLADO, 2014).…”