No abstract

Cell-suspension cultures of maize ( Zea mays L.) released soluble extracellular polysaccharides (SEPs) into their medium. Some or all of the SEPs had feruloyl ester groups. Pulse-labelling with [(3)H]arabinose was used to monitor changes in the SEPs' M(r) (estimated by gel-permeation chromatography) with time after synthesis. Newly released (3)H-SEPs were 1.3-1.6 MDa, but between 2 days and 3 days after radiolabelling (in one experiment) or between 5 days and 6 days (in another), the (3)H-SEPs abruptly increased to approximately 17 MDa, indicating extensive cross-linking. The cross-linking involved both [(3)H]xylan and [(3)H]xyloglucan components of the SEPs. The cross-links could be cleaved by alkali, returning the SEPs to their original M(r). In 0.1 M NaOH at 37 degrees C, 58% cleavage was effected within 24 h. The requirement for such prolonged alkali treatment indicates that ester-bonded (e.g. diferuloyl) groups were not solely responsible for the cross-linking. Bonds cleaved only by relatively severe alkali could include benzyl ether linkages formed between sugar residues and oxidised phenolics that had quinone methide structures. The ability of alkali to cleave the cross-links was independent of the age of the (3)H-SEP molecules. Cross-linking of (3)H-SEPs in vivo was delayed (up to approx. 7 days after radiolabelling) by exogenous sinapic acid, chlorogenic acid or rutin-agents predicted to compete with the oxidative coupling of feruloyl-polysaccharides. The cross-linking was promoted by exogenous ferulic acid or l-tyrosine, possibly because these compounds acted as precursors for polysaccharide feruloylation, thus providing additional partner substrates for the oxidative coupling of previously formed (3)H-SEPs. The ability of certain phenolics to prevent the cross-linking of (3)H-SEPs supports the idea that the cross-linking involved phenolic oxidation.

Cla.vi.bac'ter. L. n. clava cudgel; N.L. masc. n. bacter rod; N.L. masc. n. Clavibacter club‐shaped rod. Actinobacteria / Actinobacteria / Micrococcales / Microbacteriaceae / Clavibacter Pleomorphic rods (0.4–0.75 × 0.8–2.5 µm), often in angular, V‐formations with no marked rod–coccus development cycle. Gram‐stain‐positive, non‐acid‐fast, nonmotile, and nonsporeforming. Obligate aerobes; growth factors are required for growth. Acid production from carbohydrates is slow and weak ; acid is produced aerobically from glucose and glycerol. No acid is produced from adonitol, esculin, meso ‐inositol, melezitose, β‐methyl‐ D ‐glucoside, raffinose, rhamnose, or ribose. Nitrate and nitrite are not reduced or utilized; casein is not hydrolyzed. Catalase‐positive; oxidase, lipase, tyrosinase, and ureasenegative. Optimum growth temperature 20–29°C; maximum temperature for growth is 35°C. The cell‐wall peptidoglycan , based on the presence of 2 , 4‐diaminobutyric acid ( DAB ), is type B2 γ. Mycolic acids are not found. Nonhydroxylated fatty acids, specifically iso‐methyl and anteiso‐methyl branched chains fatty acids, predominate. Phosphatidylglycerol, diphosphatidylglycerol, and some unknown glycosyldiacylglycerols are the major polar lipids. Spermidine and spermine are the major polyamines with minor amounts of putrescine. Isoprenoid quinones , comprising menaquinones with 9 isoprene units ( MK‐9 ) predominate . DNA G + C content ( mol %): 65–75. Type species : Clavibacter michiganensis corrig. (Smith 1910) Davis, Gillaspie, Vidaver and Harris 1984, 113 VP ( Bacterium michiganense Smith, 1910, 794; Corynebacterium michiganense Jensen 1934, 47).