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Understanding peroxidase function in plants is difficult because of the lack of substrate specificity, the high number of genes and their diversity in structure. In the present study, the relative expression of 22 genes coding putative peroxidases (E.C 1.11.1.x) in Arabidopsis was studied. The relative expression of AtPrx37 showed a correlation with the cessation of growth in rosette leaves as well as with the growth capacity along the flower stem. Using AtPrx37::GUS construction, its expression was associated with the vascular bundles. Furthermore, the overexpression of AtPrx37 under the control of CaMV 35S promoter rendered a dwarf phenotype with smaller plants and delayed development. The plants overexpressing AtPrx37 also showed an increase in the amount of esterified phenolic material associated with their walls. A role in the growth cessation and phenolic cross-linking during lignin deposition is postulated. [ABSTRACT FROM AUTHOR]

The relationship between autolytic degradation of β(1–3),(1–4)-D-glucan and acid pH-induced extension of isolated Zea mays cell walls has been investigated using a constant-load extension technique. Acidic buffer (4.5) was able to induce an additional extension (Ea) on cell walls already extended at pH 6.8 buffer under a 20 g-mass load, indicating that the additional extension (Ea) was the parameter that better represented the effect of the different treatments on the mechanical properties of maize coleoptile cell walls. The additional extension in response to acidic pH was higher when cell walls had been previously autolysed for 24 h at pH 5.5. Furthermore, the acid-pH effect was dependent on the presence during the constant load extension of some thermo-labile factors, suggesting the participation of expansins. Acid pH increased Ea of native cell walls through an increase in the plastic extension (Ep) in agreement with a one step mechanism leading directly to irreversible (plastic) wall extension as suggested by Cosgrove (1977). The autolytic degradation of β(1–3), (1–4)-D-glucan was also able to modify the mechanical properties of maize coleoptile cell walls increasing its elastic extension (Ee) in response to pH 4.5 buffer but that modification only leads to an increase in wall extension when expansins are active, suggesting a cooperation between β-glucan turnover and expansin action. [ABSTRACT FROM AUTHOR]

The hydrolytic activity of the proteins extracted with 3 M LiCl from chick-pea (Cicer arietinum) cell walls to pec-tic fractions extracted with 50 mM trans-l,2-diaminocy-clohexane-N,N,N,N,-tetraacetic acid (CDTA) and 50 mM sodium carbonate was studied. The pectic fractions contained acidic polysaccharides with high molecular mass (higher than 5 × 103 kDa), mainly composed of uronic acids, galac-tose, arabinose and rhamnose. The extracted proteins depo-lymerized the pectic polysaccharides and also a commercial preparation of polygalacturonic acid from citrus, detected by a decrease in their viscosity and a shift of their molecular mass distribution. The extract was able to depolymerize a uronic acid-rich component in all the cases, although in different extent. Also, with regard to the CDTA-soluble pectins, a degradation of polyuronide and a shift of the molecular mass distribution of arabinogalactan was observed. [ABSTRACT FROM AUTHOR]

Growth rate, osmotic potential of the cell, cell wall mechanical properties, sugar composition and molecular weight (MW) distribution of water-soluble hemicellulosic polysaccharides of the second leaf sheath of one tall (Oryza sativa L. cv. Nihonbare) and two dwarf (Oryza sativa L. cvs. Tan-ginbozu and Waito C) cultivars of rice were compared. The effect of gibberellic acid (GA3) on the above-mentioned parameters was also studied using the tall (Nihonbare) and one of the dwarf (Waito C) cultivar. The minimum stress-relaxation time (T0) was higher in the cell wall from the two dwarfs than in the tall cultivar. Furthermore, in the water-soluble hemicellulosic polysaccharides, the mass-average MW of β-glucan was higher and that of arabinoxylan was lower in the tall cultivar than in the dwarf ones. Thus, dwarfism of cvs Tan-ginbozu and Waito C might be correlated with the different MW distributions of β-glucan and arabinoxylan. GA3 induces growth in the dwarf Waito G cultivar, decreases the T0 value of the cell wall, and also decreases the mass-average MW of water-soluble hemicelluloses. Changes in β(1–3)(1–4)glucan or arabinoxylan or in both are proposed as part of the cell wall loosening mechanism induced by gibberellin. [ABSTRACT FROM AUTHOR]

Growth rate, osmotic potential of the cell, cell wall mechanical properties, sugar composition and molecular weight (MW) distribution of water-soluble hemicellulosic polysaccharides of the second leaf sheath of one tall (Oryza sativa L. cv. Nihonbare) and two dwarf (Oryza sativa L. cvs. Tan-ginbozu and Waito C) cultivars of rice were compared. The effect of gibberellic acid (GA3) on the above-mentioned parameters was also studied using the tall (Nihonbare) and one of the dwarf (Waito C) cultivar. The minimum stress-relaxation time (T0) was higher in the cell wall from the two dwarfs than in the tall cultivar. Furthermore, in the water-soluble hemicellulosic polysaccharides, the mass-average MW of β-glucan was higher and that of arabinoxylan was lower in the tall cultivar than in the dwarf ones. Thus, dwarfism of cvs Tan-ginbozu and Waito C might be correlated with the different MW distributions of β-glucan and arabinoxylan. GA3 induces growth in the dwarf Waito G cultivar, decreases the T0 value of the cell wall, and also decreases the mass-average MW of water-soluble hemicelluloses. Changes in β(1–3)(1–4)glucan or arabinoxylan or in both are proposed as part of the cell wall loosening mechanism induced by gibberellin. [ABSTRACT FROM AUTHOR]

The changes in the molecular weight distribution of water‐soluble hemicelluloses and xyloglucan during hypocotyl growth of intact seedlings of Pinus pinaster Aiton were investigated. The mass‐average molecular weight of total polysaccharides of the hemicellulose fraction soluble in 4% KOH dramatically increased during hypocotyl growth while xyloglucan slightly decreased. These phenomena were due to an increase in the degree of polymerization of an arabinogalactan and a slight depolymer‐ization in the xyloglucan present in this fraction. In the hemicellulose fraction soluble in 24% KOH, xyloglucan increased its degree of polymerization from day 7 to 10 after which it decreased slightly. The xyloglucan of the hemicellulose fraction soluble in 4% KOH may thus be involved in cell wall loosening which makes cell wall expansion possible during hypocotyl growth. [ABSTRACT FROM AUTHOR]

The changes in pectic and hemicellulosic polysaccharides of hypocotyl cell walls during the growth of intact seedlings of Pinus pinaster Aiton were investigated, α‐Cellulose and the water‐soluble hemicellulose presented the most conspicuous changes during hypocotyl growth. The relative amount of the water‐soluble hemicellulose decreased from day 7 to day 13 when hypocotyls were in the rapid growth phase, and stabilized when hypocotyl growth ceased. In this fraction, the relative amount of non‐cellulosic glucose decreased dramatically during hypocotyl growth, while the relative amount of xylose increased. We suggest that these changes may be due to partial degradation of xyloglucan present in the water:soluble hemicellulose fraction, accompanied by the synthesis of a xylan. [ABSTRACT FROM AUTHOR]