The three branched-chain amino acids (BCAAs) are the most hydrophobic of the amino acids and play crucial roles in determining the structures of globular proteins as well as the interaction of the transmembrane domains of membranous proteins with phospholipid bilayers. However, the three BCAAs do not behave identically. In terms of protein secondary structure, valine and isoleucine exhibit a definite preference for the beta-structure, whereas leucine has a higher preference for the alpha-helix. Although mutation of one BCAA to another is commonly regarded as conservative, there are well-documented examples of such substitutions that have a significant effect on protein function. The occurrence of BCAA in nature is, therefore, attributable to their primary role in protein structure, not to their secondary metabolic roles. These functions are important for almost all proteins; therefore, BCAA commonly account for approximately 20-25% of most dietary proteins. Dietary BCAA largely escape first-pass splanchnic metabolism. The first steps in their catabolism are common to all three, involving the BCAA aminotransferase (BCAT) and branched-chain alpha-keto acid dehydrogenase (BCKD). Their further metabolism employs distinct pathways to different end-products (glucose and/or ketone bodies). However, the fact that the flux-generating step for the catabolism of the three BCAAs occurs at one of the common steps indicates that the production of these downstream products are not individually regulated and, hence, may not play important individual roles. The catabolism of the BCAAs is highly regulated by both allosteric and covalent mechanisms. BCKD is inhibited by phosphorylation and activated by dephosphorylation. Allosteric inhibition of the kinase by the branched-chain keto acids (BCKA) (particularly by alpha-ketoisocaproate) serves both as a mechanism for promoting the catabolism of excess quantities of these amino acids as well as for conserving low concentrations of these dietary essential amino acids. Cytosolic and mitochondrial isoenzymes of BCAT have been identified. They are thought to play an important role in brain neurotransmitter metabolism.

Significant gaps remain in our knowledge of the pathways of amino acid catabolism in humans. Further quantitative data describing amino acid metabolism in the kidney are especially needed as are further details concerning the pathways utilized for certain amino acids in liver. Sufficient data do exist to allow a broad picture of the overall process of amino acid oxidation to be developed along with approximate quantitative assessments of the role played by liver, muscle, kidney, and small intestine. Our analysis indicates that amino acids are the major fuel of liver, i.e., their oxidative conversion to glucose accounts for about one-half of the daily oxygen consumption of the liver, and no other fuel contributes nearly so importantly. The daily supply of amino acids provided in the diet cannot be totally oxidized to CO2 in the liver because such a process would provide far more ATP than the liver could utilize. Instead, most amino acids are oxidatively converted to glucose. This results in an overall ATP production during amino acid oxidation very nearly equal to the ATP required to convert amino acid carbon to glucose. Thus gluconeogenesis occurs without either a need for ATP from other fuels or an excessive ATP production that could limit the maximal rate of the process. The net effect of the oxidation of amino acids to glucose in the liver is to make nearly two-thirds of the total energy available from the oxidation of amino acids accessible to peripheral tissues, without necessitating that peripheral tissues synthesize the complex array of enzymes needed to support direct amino acid oxidation. As a balanced mixture of amino acids is oxidized in the liver, nearly all carbon from glucogenic amino acids flows into the mitochondrial aspartate pool and is actively transported out of the mitochondria via the aspartate-glutamate antiport linked to proton entry. In the cytoplasm the aspartate is converted to fumarate utilizing urea cycle enzymes; the fumarate flows via oxaloacetate to PEP and on to glucose. Thus carbon flow through the urea cycle is normally interlinked with gluconeogenic carbon flow because these metabolic pathways share a common step. Liver mitochondria experience a severe nonvolatile acid load during amino acid oxidation. It is suggested that this acid load is alleviated mainly by the respiratory chain proton pump in a form of uncoupled respiration.(ABSTRACT TRUNCATED AT 400 WORDS)

has been suggested to correspond with various anatomical and morphological plant characteristics. These char- Evaluations of Kentucky bluegrass (Poa pratensis L.) wear toler-acteristics include total cell wall content (TCW), quanance have been conducted; however, studies investigating wear mechanisms within this species is limited. This information would be valuable tity of schlerenchyma fibers, leaf width and leaf tensile in selecting wear tolerant genotypes. The objective of this study was strength, and shoot density (and verdure) (Shearman to identify anatomical and morphological characteristics in diverse and Beard, 1975band Beard, , 1975c. wear tolerant Kentucky bluegrasses. Wear treatments were applied Studies by Shearman and Beard (1975c) and Trento the 2000 National Turfgrass Evaluation Program (NTEP) Kentucky holm et al. (2000) have focused on the constituents of bluegrass field plots in the fall of 2002 at the University of Massachucell walls as a principle means of explaining turfgrass setts Joseph Troll Turf Research Center at South Deerfield, MA.wear tolerance. Cell wall components include cellulose, Wear treatments were applied to 173 genotypes with a differential hemicellulose, and lignin (Taiz and Zeiger, 1972). Celluslip-wear apparatus, and plots were visually rated for wear injury.lose is a tightly packed group of polysaccharide chains The 10 most wear tolerant (TOL) and intolerant (INTOL) genotypes that provides plant tissues with a high tensile strength. were selected for further evaluation. Twelve characteristics were measured in 2003 and 2004 comparing TOL and INTOL genotypes in This suggests that plants with higher percentages of field plots and as greenhouse grown spaced-plants. Characteristics cellulose may be more tolerant to wear stress. Hemiincluded tiller density, shoot fresh weight and dry weight, shoot water celluloses are a heterogeneous group of polysaccharides content, leaf turgidity, number of leaves per shoot, leaf width, leaf that bind to cellulose to further strengthen cell walls. strength, leaf angle, and leaf cell wall constituents [total cell wall Lignin is a highly branched polymer of phenylpropanoid content (TCW), hemicellulose, and lignocellulose]. Not all differences groups that possesses high mechanical rigidity and thereobserved in the greenhouse were present in field plots. Significant fore strengthens stems and vascular tissues (Taiz and differences were found between genotypes and TOL and INTOL Zeiger, 1972). Because of its physical toughness, lignin groupings. No significant interaction with year was detected. Tolerant deters feeding by animals (van Soest, 1994) and theregenotypes were associated with a more vertical leaf angle, greater fore may play a role in wear tolerance. TCW and lignocellulose content, and a lower shoot moisture content and leaf turgidity. Leaf angle was the single most important attribute Anatomical characteristics unique to the cell walls of separating wear TOL and INTOL genotypes. Biological explanation wear tolerant species have been ana...

Main ConclusionThis is a first report of an Ala-205-Phe substitution in acetolactate synthase conferring resistance to imidazolinone, sulfonylurea, triazolopyrimidines, sulfonylamino-carbonyl-triazolinones, and pyrimidinyl (thio) benzoate herbicides.Resistance to acetolactate synthase (ALS) and photosystem II inhibiting herbicides was confirmed in a population of allotetraploid annual bluegrass (Poa annua L.; POAAN-R3) selected from golf course turf in Tennessee. Genetic sequencing revealed that seven of eight POAAN-R3 plants had a point mutation in the psbA gene resulting in a known Ser-264-Gly substitution on the D1 protein. Whole plant testing confirmed that this substitution conferred resistance to simazine in POAAN-R3. Two homeologous forms of the ALS gene (ALSa and ALSb) were detected and expressed in all POAAN-R3 plants sequenced. The seven plants possessing the Ser-264-Gly mutation conferring resistance to simazine also had a homozygous Ala-205-Phe substitution on ALSb, caused by two nucleic acid substitutions in one codon. In vitro ALS activity assays with recombinant protein and whole plant testing confirmed that this Ala-205-Phe substitution conferred resistance to imidazolinone, sulfonylurea, triazolopyrimidines, sulfonylamino-carbonyl- triazolinones, and pyrimidinyl (thio) benzoate herbicides. This is the first report of Ala-205-Phe mutation conferring wide spectrum resistance to ALS inhibiting herbicides.Electronic supplementary materialThe online version of this article (doi:10.1007/s00425-015-2399-9) contains supplementary material, which is available to authorized users.

Methiozolin is a new isoxazoline herbicide being investigated for selective POST annual bluegrass control in creeping bentgrass putting greens. Glasshouse and field research was conducted from 2010 to 2012 in Tennessee and Texas to evaluate annual bluegrass control efficacy with methiozolin. Application placement experiments in the glasshouse illustrated that root absorption was required for POST annual bluegrass control with methiozolin at 1,000 g ai ha−1. Soil-plus-foliar and soil-only applications of methiozolin reduced annual bluegrass biomass greater than treatments applied foliar-only. Field experiments evaluated annual bluegrass control efficacy with two application rates (500 and 1,000 g ha−1) and six application regimes (October, November, December, October followed by [fb] November, November fb December, and October fb November fb December) on sand- and soil-based putting greens. Annual bluegrass control with methiozolin at 1,000 g ha−1on sand-based greens ranged from 70 to 72% compared to 87 to 89% on soil-based greens. Treatment at 500 g ha−1controlled annual bluegrass 57 to 64% on sand-based greens compared to 72 to 80% on soil-based greens. Most sequential methiozolin application regimes controlled annual bluegrass more than single applications. On sand-based greens, sequential application programs controlled annual bluegrass 70 to 79% compared to 85 to 92% on soil-based greens. Responses indicate that methiozolin is a root-absorbed herbicide with efficacy for selective control of annual bluegrass in both sand- and soil-based creeping bentgrass putting greens.

Indaziflam controls annual grassy weeds by inhibiting cellulose biosynthesis. Research was conducted from 2008 to 2011 in Tennessee, Texas, and Georgia evaluating the efficacy of indaziflam for PRE and POST control of annual bluegrass in bermudagrass turf. In Texas, indaziflam at 30, 40, 50, and 60 g ai ha−1 applied PRE provided 93 to 100% annual bluegrass control through 28 wk after treatment. When applied PRE at 80 g ai ha−1 and at 4, 8, and 12 wk after PRE (WAP), indaziflam controlled annual bluegrass 67 to 100% 32 wk after initial treatment (WAIT) in Tennessee; however, reduced efficacy was observed with 12 WAP treatments in a single year of a 2-yr study. Similarly, annual bluegrass control with PRE applications or with 4 and 8 WAP applications of indaziflam at 35 and 52.5 g ai ha−1 ranged from 88 to 100% at 30 WAIT in Tennessee. In Georgia, these rates of indaziflam applied PRE and 4 WAP controlled annual bluegrass 96 to 100% on all evaluation dates and resulted in 97 to 100% reduction in plant counts relative to the untreated control at 30 WAIT. When applied 8 WAP, the 35 and 52.5 g ai ha−1 rates of indaziflam controlled annual bluegrass only 51 to 71% at 30 WAIT in Georgia. Although increasing the application rate of indaziflam treatments 8 WAP provided greater annual bluegrass control, each rate provided significantly lower control when applied 8 WAP compared with PRE or at 4 WAP. No bermudagrass injury was observed in this research. Results suggest indaziflam provides effective PRE and early POST control of annual bluegrass in bermudagrass turf. However, additional research is needed to determine the effects of plant size and maturity on indaziflam efficacy for POST annual bluegrass control.

Indaziflam is an alkylazine herbicide that controls annual grasses by inhibiting cellulose biosynthesis. Compared with other PRE herbicides like prodiamine, indaziflam has a longer half-life in soil (> 150 d), which may allow for greater flexibility with application timing. Research was conducted in 2010 in Tennessee and Georgia evaluating smooth crabgrass control efficacy with indaziflam applied at early PRE, PRE, and early POST timings on the basis of soil temperature. Regardless of application timing, all rates of indaziflam (35, 52.5, and 70 g ai ha−1) controlled smooth crabgrass 89 to 100%. Prodiamine at 840 g ai ha−1applied PRE provided ≥ 99% smooth crabgrass control on all rating dates. Smooth crabgrass plant counts were significantly correlated (r= −0.961; p < 0.0001) with visual ratings of smooth crabgrass control at the end of the study. Application flexibility with indaziflam may benefit turf managers in scheduling herbicide applications for smooth crabgrass control in Tennessee and Georgia.

Goosegrass is a problematic summer annual weed in cotton, soybean, and corn production in the southern United States. Glyphosate is labeled for POST control of goosegrass in glyphosate-resistant (GR) cotton, soybean, and corn production. A population of goosegrass in west Tennessee not controlled by glyphosate was examined in greenhouse and laboratory studies. At 21 days after treatment (DAT), a glyphosate-susceptible (SS) biotype was controlled > 90% with glyphosate at rates greater than 210 g ae ha−1. Comparatively, the GR biotype was only controlled 12% at 210 g ae ha−1. Using goosegrass control data, I50values for GR and SS biotypes were 868 and 117 g ae ha−1, susceptibility, resulting in a resistance factor (RF) of 7.4. Treatment with glyphosate at 210 g ae ha−1reduced fresh weight biomass of the SS biotype to 5 g per pot compared to 36 g for the GR biotype. A total of 3,360 g ae ha−1glyphosate was required to reduce fresh weights of the GR biotype to ∼5 g per pot. Using fresh and dry weight biomass data, I50values for the GR biotype were 3 to 10 times greater than the SS biotype. On each date from 1 to 6 DAT the SS biotype accumulated higher concentrations of shikimate than the GR biotype. Future research should evaluate strategies for managing GR goosegrass with alternative modes of action. To prevent the spread of resistance, additional research evaluating programs for managing glyphosate-susceptible goosegrass in GR crops is also warranted.