Alfalfa stems, reed canarygrass, and switchgrass; perennial herbaceous species that have potential as biomass energy crops in temperate regions; were evaluated for their bioconversion potential as energy crops. Each forage species was harvested at two or three maturity stages and analyzed for carbohydrates, lignin, protein, lipid, organic acids, and mineral composition. The biomass samples were also evaluated for sugar yields following pretreatment with dilute sulfuric followed by enzymatic saccharification using a commercial cellulase preparation. Total carbohydrate content of the plants varied from 518 to 655 g kg À1 dry matter (DM) and cellulose concentration from 209 to 322 g kg À1 DM. Carbohydrate and lignin contents were lower for samples from early maturity samples compared to samples from late maturity harvests. Several important trends were observed in regards to the efficiency of sugar recovery following treatments with dilute acid and cellulase. First, a significant amount of the available carbohydrates were in the form of soluble sugars and storage carbohydrates (4.3-16.3% wt/wt). Recovery of soluble sugars following dilute acid pretreatment was problematic, especially that of fructose. Fructose was found to be extremely labile to the dilute acid pretreatments. Second, the efficiency at which available glucose was recovered was inversely correlated to maturity and lignin content. However, total glucose yields were higher for the later maturities because of higher cellulose contents compared to the earlier maturity samples. Finally, cell wall polysaccharides, as determined by the widely applied detergent fiber system were found to be inaccurate. The detergent fiber method consistently overestimated cellulose and hemicellulose and underestimated lignin by substantial amounts.

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Duff. S. M. G.. Sarath, G. and Plaxton, W. C. 1994. The role of acid phosphatases in plant phosphorus metabolism. -Physiol. Plant. 90; 791-800.Hydrolysis of phosphate esters is a critical process in the energy metabolism and metabolic regulation of plant ceils. This review summarizes the characteristics and putative roles of piant acid phosphatase lAPasel. Although immunologicaliy closely related, plant APases display remarkable heterogeneity w ith regards to their kinetic and molecular properties, and subcellular location. The secreted APa.ses of roots and cell cultures are relati\ ely non-specific enzymes that appear to be important in the hydrolysis and mobilization of P, from extracellular phosphomonoesters for plant nutrition. Intracelluiar APases are undoubtedly involved in the routine utilization of P, reserves or other P, containing compounds. A special class of intracellular APase exists that demonstrate a clear-cut (but generally nonabsoiute) substrate selectivity. These .^.Pases are hypothesized to have distinct metabolic functions and include; phytase, phosphoglycoiate phosphatase. 3-pbosphoglycerate phosphatase. phosphoenolpyruvate phosphatase. and phosphotyrosyl-protein phosphatase. APase expression is regulated by a variety of developmental and environmental factors. P, starvation induces de novo synthesis of extra-and intracellular APases in cell cultures as well as in whole plants.Recommendations are made to achieve uniformity in the analyses of the different .A.Pase isoforms normally encountered within and between different plant tissues.Key words -.\cid phosphatase. isozymes. phosphate metabolism, phosphoenolpyruvate phosphatase. 3-phosphoglycerate phosphatase, phospboglycolate phosphatase, pho.sphoprotein phosphatase. phytase..

Lignin is known to impede conversion of lignocellulose into ethanol. In this study, forage sorghum plants carrying brown midrib (bmr) mutations, which reduce lignin contents, were evaluated as bioenergy feedstocks. The near-isogenic lines evaluated were: wild type, bmr-6, bmr-12, and bmr-6 bmr-12 double mutant. The bmr-6 and bmr-12 mutations were equally efficient at reducing lignin contents (by 13% and 15%, respectively), and the effects were additive (27%) for the double mutant. Reducing lignin content was highly beneficial for improving biomass conversion yields. Sorghum biomass samples were pretreated with dilute acid and recovered solids washed and hydrolyzed with cellulase to liberate glucose. Glucose yields for the sorghum biomass were improved by 27%, 23%, and 34% for bmr-6, bmr-12, and the double mutant, respectively, compared to wild type. Sorghum biomass was also pretreated with dilute acid followed by co-treatment with cellulases and Saccharomyces cerevisiae for simultaneous saccharification and fermentation (SSF) into ethanol. Conversion of cellulose to ethanol for diluteacid pretreated sorghum biomass was improved by 22%, 21%, and 43% for bmr-6, bmr-12, and the double mutant compared to wild type, respectively. Electron microscopy of dilute-acid treated samples showed an increased number of lignin globules in double-mutant tissues as compared to the wild-type, suggesting the lignin had become more pliable. The mutations were also effective for improving ethanol yields when the (degrained) sorghum was pretreated with dilute alkali instead of dilute acid. Following pretreatment with dilute ammonium hydroxide and SSF, ethanol conversion yields were 116 and 130 mg ethanol/g dry biomass for the double-mutant samples and 98 and 113 mg/g for the wild-type samples.

The bis-histidyl heme coordination found in riceHb1 is unusual for a protein that binds O(2) reversibly. However, the distal His73 is rapidly displaced by ferrous ligands, and the overall O(2) affinity is ultra-high (K(D) approximately 1 nM). Our crystallographic model suggests that ligand binding occurs by an upward and outward movement of the E helix, concomitant dissociation of the distal histidine, possible repacking of the CD corner and folding of the D helix. Although the functional relevance of quaternary structure in nsHbs is unclear, the role of two conserved residues in stabilizing the dimer interface has been identified.

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brown midrib6 (bmr6) affects phenylpropanoid metabolism, resulting in reduced lignin concentrations and altered lignin composition in sorghum (Sorghum bicolor). Recently, bmr6 plants were shown to have limited cinnamyl alcohol dehydrogenase activity (CAD; EC 1.1.1.195), the enzyme that catalyzes the conversion of hydroxycinnamoyl aldehydes (monolignals) to monolignols. A candidate gene approach was taken to identify Bmr6. Two CAD genes (Sb02g024190 and Sb04g005950) were identified in the sorghum genome based on similarity to known CAD genes and through DNA sequencing a nonsense mutation was discovered in Sb04g005950 that results in a truncated protein lacking the NADPH-binding and C-terminal catalytic domains. Immunoblotting confirmed that the Bmr6 protein was absent in protein extracts from bmr6 plants. Phylogenetic analysis indicated that Bmr6 is a member of an evolutionarily conserved group of CAD proteins, which function in lignin biosynthesis. In addition, Bmr6 is distinct from the other CAD-like proteins in sorghum, including SbCAD4 (Sb02g024190). Although both Bmr6 and SbCAD4 are expressed in sorghum internodes, an examination of enzymatic activity of recombinant Bmr6 and SbCAD4 showed that Bmr6 had 1 to 2 orders of magnitude greater activity for monolignol substrates. Modeling of Bmr6 and SbCAD4 protein structures showed differences in the amino acid composition of the active site that could explain the difference in enzyme activity. These differences include His-57, which is unique to Bmr6 and other grass CADs. In summary, Bmr6 encodes the major CAD protein involved in lignin synthesis in sorghum, and the bmr6 mutant is a null allele.

G. 2006. Switchgrass as a biofuels feedstock in the USA. Can. J. Plant Sci. 86: 1315-1325. Switchgrass (Panicum virgatum L.) has been identified as a model herbaceous energy crop for the USA. In this review, we selectively highlight current USDA-ARS research on switchgrass for biomass energy. Intensive research on switchgrass as a biomass feedstock in the 1990s greatly improved our understanding of the adaptation of switchgrass cultivars, production practices, and environmental benefits. Several constraints still remain in terms of economic production of switchgrass for biomass feedstock including reliable establishment practices to ensure productive stands in the seeding year, efficient use of fertilizers, and more efficient methods to convert lignocellulose to biofuels. Overcoming the biological constraints will require genetic enhancement, molecular biology, and plant breeding efforts to improve switchgrass cultivars. New genomic resources will aid in developing molecular markers, and should allow for marker-assisted selection of improved germplasm. Research is also needed on profitable management practices for switchgrass production appropriate to specific agro-ecoregions and breakthroughs in conversion methodology. Current higher costs of biofuels compared to fossil fuels may be offset by accurately valuing environmental benefits associated with perennial grasses such as reduced runoff and erosion and associated reduced losses of soil nutrients and organic matter, increased incorporation of soil carbon and reduced use of agricultural chemicals. Use of warm-season perennial grasses in bioenergy cropping systems may also mitigate increases in atmospheric CO 2 . A critical need is teams of scientists, extension staff, and producer-cooperators in key agro-ecoregions to develop profitable management practices for the production of biomass feedstocks appropriate to those agro-ecoregions.