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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]

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]

A complete cDNA from Pinus pinaster Aiton, potentially coding for an alpha-xylosidase able to remove the xylose residue from xyloglucan oligosaccharides, has been cloned. Its sequence was homologous to previously published alpha-xylosidase genes from Arabidopsis and nasturtium. The protein also showed the two signature regions of family 31 of glycosyl hydrolases. The gene expression level was quantified by competitive RT-PCR, under different growth conditions, throughout seedling development, in different regions along the hypocotyls and in auxin-treated hypocotyl segments, and related with growth capacity and alpha-xylosidase activity. A role of alpha-xylosidase in regulating the level of xyloglucan oligosaccharides within the apoplast is proposed. The action of an alpha-xylosidase removing the xylose residue, would make possible the action of a beta-glucosidase deblocking the xyloglucan oligosaccharide degradation and it could serve as a control point for the regulation of the apoplastic levels of xyloglucan oligosaccharides.