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.

Aluminum oxide nanoparticles affect the cell wall structure and lignin composition slightly altering the soybean growth.

Aluminum oxide (Al2O3) nanoparticles (NPs) are among the nanoparticles most used industrially, but their impacts on living organisms are widely unknown. We evaluated the effects of 50-1000 mg L-1 Al2O3 NPs on the growth, metabolism of lignin and its monomeric composition in soybean plants. Al2O3 NPs did not affect the length of roots and stems. However, at the microscopic level, Al2O3 NPs altered the root surface inducing the formation of cracks near to root apexes and damage to the root cap. The results suggest that Al2O3 NPs were internalized and accumulated into the cytosol and cell wall of roots, probably interacting with organelles such as mitochondria. At the metabolic level, Al2O3 NPs increased soluble and cell wall-bound peroxidase activities in roots and stems but reduced phenylalanine ammonia-lyase activity in stems. Increased lignin contents were also detected in roots and stems. The Al2O3 NPs increased the p-hydroxyphenyl monomer levels in stems but reduced them in roots. The total phenolic content increased in roots and stems; cell wall-esterified p-coumaric and ferulic acids increased in roots, while the content of p-coumaric acid decreased in stems. In roots, the content of ionic aluminum (Al+3) was extremely low, corresponding to 0.0000252% of the aluminum applied in the nanoparticulate form. This finding suggests that all adverse effects observed were due to the Al2O3 NPs only. Altogether, these findings suggest that the structure and properties of the soybean cell wall were altered by the Al2O3 NPs, probably to reduce its uptake and phytotoxicity.

Exogenous application of rosmarinic acid improves saccharification without affecting growth and lignification of maize.

Biomimetically incorporated into the lignin structure, rosmarinic acid improves in vitro maize cell wall saccharification; however, no in planta studies have been performed. We hypothesized that rosmarinic acid, itself, could inducer saccharification without disturbing plant growth. Its effects on growth, enzymes of the phenylpropanoid pathway, lignin, monomeric composition, and saccharification of maize were evaluated. In a short-term (24 h) exposure, rosmarinic acid caused deleterious effects on maize roots, inhibiting the first enzymes of the phenylpropanoid pathway, phenylalanine ammonia-lyase and tyrosine ammonia-lyase, altering lignin composition and slightly increasing saccharification. In a long-term (14 d) exposure, rosmarinic acid increased saccharification of maize stems by about 50% without any deleterious effects on plant growth, the phenylpropanoid pathway and lignin formation. This demonstrated that exogenous application of rosmarinic acid on maize plants improved saccharification, and represented an interesting approach in facilitating enzymatic hydrolysis of biomass polysaccharides and increasing bioethanol production.