Sugarcane cell wall structure and lignin distribution investigated by confocal and electron microscopy

Abstract

Lignocellulosic plant cell wall is considered a potential source for second generation biofuels. The plant cell wall is a highly complex structure mainly composed of cellulose, hemicelluloses, and lignin that form a network of crosslinked fibers. The structural organization of the sugarcane cell wall has not been previously analyzed in detail, and this analysis is a prerequisite for further studies on the recalcitrance and deconstruction of its biomass. In this work, cellulose and lignin localization were investigated by confocal laser scanning microscopy. In addition, the internode sugarcane cell wall structural organization was analyzed by electron microscopy. Internode stem anatomy showed a typical monocot structure consisting of epidermis, hypoderm, and vascular bundles scattered throughout ground parenchyma tissue and surrounded by sclerenchyma fibers. Confocal images of safranin labeled sugarcane showed that lignin distribution was predominant in the vessel elements, cell wall corners (CC), and middle lamella (ML), while cellulose-rich cell walls were randomly distributed in the ML and organized in the other cell wall layers. KMnO4 cytochemistry revealed that lignin was predominantly distributed in secondary cell walls, ML and CC. Cell wall sublayers (S1, S2, and S3) were identified and measured by transmission electron microscopy. Our results provide insights that may help further understanding of sugarcane cell wall organization, which is crucial for the research and technology of plant-based biofuel production.

Vascular development in very young conifer seedlings: Theoretical hydraulic capacities and potential resistance to embolism

“…Sections were optically scanned using an Olympus Fluoview 1000 (FV‐1000) confocal microscope (Olympus America, Center Valley, Pennsylvania, USA) with excitation of three laser lines at 405, 488, and 559 nm and three emission filters (SDM490, SDM560 and BF, respectively). The ranges of these emission filters were 425–475 nm, 500–545 nm, and 575–675 nm, respectively, but each range could be further restricted to better distinguish specific anatomical characteristics of interest (Bond et al, 2008; Sant'Anna et al, 2013). Narrowing the range of SDM560 and BF filters to 520–540 nm and 575–620 nm, respectively, often reduced background cellular noise, making the cell walls easier to view.…”

Caracterização ultraestrutural e hidrólise enzimática de cana-de-açúcar e bagaço pré-tratado quimio-mecanicamente

“…As setas indicam os feixes fibrovasculares (a) e as células de parênquima (b) (adaptado SANT'ANNA et al, 2013) …”

“…Os feixes fibrovasculares são responsáveis pelo transporte e suporte mecânico, em geral são compostos pelos vasos xilema e floema, circundados pelas fibras. Os feixes estão espalhados nos colmos, porém mais densamente presentes na sua periferia e ficam cercados por células de parênquima (DRIEMEIER et al, 2012;SANT'ANNA et al, 2013). As fibras, devido a sua função de suporte mecânico, apresentam dimensões de 15-25 µm de largura e 0,6-1,7 mm de comprimento, paredes grossas (4 µm) e um menor lúmen, diferentemente dos vasos e do parênquima, que apresentam 2,7 µm e 1,7 µm, respectivamente, de espessura da parede celular (SANJUAN et al, 2001).…”

“…A parede secundária é constituída por três camadas (S1, S2 e S3). Essas camadas S1, S2 e S3 apresentam espessura variável 100-200nm, 400-500nm, 220-300nm, respectivamente, e com distintas orientações das fibrilas de celulose embebidas em uma matriz composta por hemicelulose e lignina (SANT'ANNA et al, 2013). As células encontram-se separadas pela lamela média (LM), que é uma camada fina (máximo 1 μm de espessura), composta por elevada concentração de lignina (Figura 3).…”

“…Fonte: SANT'ANNA et al, 2013. A composição química do bagaço varia em função da variedade de cana, do solo, do clima, da disponibilidade de água e da época na safra, dentre outros aspectos. Sua composição é de aproximadamente 40-50% de celulose, 25% de hemicelulose, 25% de lignina, 2% de cinzas e 5% de extrativos (FENGEL;WEGENER,1989;PANDEY et al, 2000;SAHA, 2003).…”