Increased Gibberellins and Light Levels Promotes Cell Wall Thickness and Enhance Lignin Deposition in Xylem Fibers

Light intensity and hormones (gibberellins; GAs) alter plant growth and development. A fine regulation triggered by light and GAs induces changes in stem cell walls (CW). Cross-talk between light-stimulated and GAs-induced processes as well as the phenolic compounds metabolism leads to modifications in lignin formation and deposition on cell walls. How these factors (light and GAs) promote changes in lignin content and composition. In addition, structural changes were evaluated in the stem anatomy of tobacco plants. GA3 was sprayed onto the leaves and paclobutrazol (PAC), a GA biosynthesis inhibitor, via soil, at different irradiance levels. Fluorescence microscopy techniques were applied to detect lignin, and electron microscopy (SEM and TEM) was used to obtain details on cell wall structure. Furthermore, determination of total lignin and monomer contents were analyzed. Both light and GAs induces increased lignin content and CW thickening as well as greater number of fiber-like cells but not tracheary elements. The assays demonstrate that light exerts a role in lignification under GA3 supplementation. In addition, the existence of an exclusive response mechanism to light was detected, that GAs are not able to replace

Plant cell wall composition and enzymatic deconstruction

Cellulosic ethanol is one the most prominent technologies capable of replacing the use of fossil fuels in an observable horizon of technological development. The complexity of plant biomass, however, continues to challenge our ability to convert it into biofuels efficiently. Highly complex and cross-linked polysaccharides, hydrophobic and protein adsorbent polymers, and crystalline supramolecular structures comprise some of the structures that shield the plant cell contents (and the shield structures themselves) against predators. In response, a sophisticated enzymatic weaponry, with its associated chemical and physical mechanisms, is necessary to overcome this recalcitrance. Here we describe basic information about chemical composition of lignocellulosic biomass and the enzymatic arsenal for lignocellulose deconstruction into fermentable sugars

Inhibiting tricin biosynthesis improves maize lignocellulose saccharification.

Lignin is a technological bottleneck to convert polysaccharides into fermentable sugars, and different strategies of genetic-based metabolic engineering have been applied to improve biomass saccharification. Using maize seedlings grown hydroponically for 24 h, we conducted a quick non-transgenic approach with five enzyme inhibitors of the lignin and tricin pathways. Two compounds [3,4-(methylenedioxy)cinnamic acid: MDCA and 2,4-pyridinedicarboxylic acid: PDCA] revealed interesting findings on root growth, lignin composition, and saccharification. By inhibiting hydroxycinnamoyl-CoA ligase, a key enzyme of phenylpropanoid pathway, MDCA decreased the lignin content and improved saccharification, but it decreased root growth. By inhibiting flavone synthase, a key enzyme of tricin biosynthesis, PDCA decreased total lignin content and improved saccharification without affecting root growth. PDCA was three-fold more effective than MDCA, suggesting that controlling lignin biosynthesis with enzymatic inhibitors may be an attractive strategy to improve biomass saccharification

Furfural and hydroxymethylfurfural contents in sugarcane bagasse, soybean root and soybean seed coat determined after the acetyl bromide assay.

<p>Mean values ± SE (N = 3).</p

Contributions of ash, insoluble and soluble lignin concentration for total Klason lignin.

<p>Contributions of ash, insoluble and soluble lignin concentration for total Klason lignin.</p

Lignin monomer composition of sugarcane bagasse, soybean root and soybean seed coat.

<p>H, <i>p</i>-hydroxyphenyl; G, guaiacyl; and S, syringyl monomers. Mean values ± SE (N = 6) marked with different letters, in lines, are significantly different (P≤0.05, Scott-Knott test).</p><p>Lignin monomer composition of sugarcane bagasse, soybean root and soybean seed coat.</p

Lignin content of sugarcane bagasse, soybean root and soybean seed coat determined by the acetyl bromide, Klason lignin and thioglycolic acid methods.

<p>AB: acetyl bromide method; TGA: thioglycolic acid method. Mean values ± SE (N = 4) marked with different letters are significantly different (P≤0.05, Scott-Knott test).</p

The Acetyl Bromide Method Is Faster, Simpler and Presents Best Recovery of Lignin in Different Herbaceous Tissues than Klason and Thioglycolic Acid Methods

We compared the amount of lignin as determined by the three most traditional methods for lignin measurement in three tissues (sugarcane bagasse, soybean roots and soybean seed coat) contrasting for lignin amount and composition. Although all methods presented high reproducibility, major inconsistencies among them were found. The amount of lignin determined by thioglycolic acid method was severely lower than that provided by the other methods (up to 95%) in all tissues analyzed. Klason method was quite similar to acetyl bromide in tissues containing higher amounts of lignin, but presented lower recovery of lignin in the less lignified tissue. To investigate the causes of the inconsistencies observed, we determined the monomer composition of all plant materials, but found no correlation. We found that the low recovery of lignin presented by the thioglycolic acid method were due losses of lignin in the residues disposed throughout the procedures. The production of furfurals by acetyl bromide method does not explain the differences observed. The acetyl bromide method is the simplest and fastest among the methods evaluated presenting similar or best recovery of lignin in all the tissues assessed