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Regulation of α-galactosidase activity and the hydrolysis of galactomannan in the endosperm of the fenugreek (Trigonella foenum-graecum L.) seed (1985)

Spyropoulos, C. G. ; Reid, J. S. G.

Springer

Planta 166 (1985), S. 271-275

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ISSN: 1432-2048

Keywords: Endosperm ; Galactomannan ; α-Galactosidase ; Germination (seed) ; Seed germination ; Trigonella

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract When endosperms were isolated from fenugreek seeds 5 h after sowing and incubated in a small volume of water, the development of α-galactosidase activity and the breakdown of the galactomannan storage polysaccharide were both inhibited relative to control endosperms incubated in larger volumes. The inhibition could be relieved by pre-washing the endosperms, and reimposed by the wash-liquors. If the endosperms were isolated 24 h after sowing, no inhibition was observed. Removal of the embryonic axis from germinating fenugreek seeds and from germinated seedlings also inhibited the development of α-galactosidase activity and galactomannan breakdown in the endosperms; the inhibition was more pronounced the earlier the axis was removed. Axis excision 5 h after sowing caused a delay in the onset of galactomannan breakdown and of the appearance of α-galactosidase activity in the endosperms. It also led to a decrease in the rates of galactomannan breakdown and α-galactosidase production. Axis excision 24 h after sowing caused only a slowing of the rates of galactomannan breakdown and α-galactosidase increase. The inhibition caused by axis removal at 5 h could be relieved partially by gibberellin (10-4 M), benzyladenine (10-5 M), mixtures of these and by the herbicide SAN 9789 [4-chloro-5-(methylamine)-2-(α,α,α-trifluoro-m-tolyl)-3-(2H)-pyridazinone]. These substances had no effect on the inhibition caused by axis-removal at 24 h. Excision of the cotyledons at 5 h-leaving the separated axis and the endosperm-also caused inhibition of galactomannan breakdown and α-galactosidase development. The results are consistent with the presence in the fenugreek seed endosperm of diffusible inhibitors of galactomannan mobilisation which are removed or inactivated during normal germination and early seedling development. They are also consistent with a role for the seedling axis in the control of galactomannan breakdown in the endosperm. Initially the axis appears to have a regulatory function (via gibberellins and/or cytokinins?) in determining the onset of α-galactosidase production in the endosperm. Thereafter its continued presence is necessary to ensure maximal rates of α-galactosidase production and galactomannan hydrolysis. The role of the axis may be initially to counteract the endogenous inhibitors in the endosperm and then to act as a sink for the galactomannan breakdown products released in the endosperm and taken up by the cotyledons.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00397359

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Enzyme specificity in galactomannan biosynthesis (1995)

Reid, J. S. Grant ; Edwards, Mary ; Gidley, Michael J. ; [et al.]

Springer

Planta 195 (1995), S. 489-495

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ISSN: 1432-2048

Keywords: Biosynthesis (computer simulation) ; Cell wall (plant) ; Cyamopsis ; Galactomannan ; Senna ; Trigonella

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Membrane-bound enzymes from developing legume-seed endosperms catalyse galactomannan biosynthesis in vitro from GDP-mannose and UDP-galactose. A mannosyltransferase [mannan synthase] catalyses the extension of the linear (1→4)-β-linked d-mannan backbone towards the non-reducing end. A specific α-galactosyltransferase brings about the galactosyl-substitution of the backbone by catalysing the transfer of a (1→6)-α-d-galactosyl residue to an acceptor mannosyl residue at or close to the non-reducing terminus of the growing backbone. Labelled galactomannans with a range of mannose/galactose (Man/Gal) ratios were formed in vitro from GDP-[14C]mannose and UDP-[14C]galactose using membrane-bound enzyme preparations from fenugreek (Trigonella foenum-graecum L.), guar (Cyamopsis tetragonoloba (L.) Taub.) and senna (Senna occidentalis (L.) Link.), species which in vivo, form galactomannans with Man/Gal ratios of 1.1, 1.6 and 3.3 respectively. The labelled galactomannans were fragmented using a structure-sensitive endo-(1→4)-β-d-mannanase and the quantitative fragmentation data were processed using a computer algorithm which simulated the above model for galactomannan biosynthesis on the basis of a second-order Markov chain process, and also the subsequent action of the endo-mannanase. For each galactomannan data-set processed, the algorithm generated a set of four conditional probabilities required by the Markov model. The need for a second-order Markov chain description indicated that the galactomannan subsite recognition sequence of the galactosyltransferase must encompass at least three backbone mannose residues, i.e. the site of substitution and the two preceding ones towards the reducing end of the growing galactomannan chain. Data-sets from the three plant species generated three distinctly different sets of probabilities, and hence galactose-substitution rules. For each species, the maximum degree of galactose-substitution consistent with these rules was closely similar to that observed for the primary product of galactomannan biosynthesis in vivo. The data provide insight into the mechanism of action and the spatial organisation of membrane-bound polysaccharide synthases.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00195705

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Xyloglucan (amyloid) mobilisation in the cotyledons of Tropaeolum majus L. seeds following germination (1985)

Edwards, Mary ; Dea, Iain C. M. ; Bulpin, Paul V. ; [et al.]

Springer

Planta 163 (1985), S. 133-140

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ISSN: 1432-2048

Keywords: Amyloid (seed) ; Endo-β-glucanase ; β-Galactosidase ; Germination (seed) ; β-Glucosidase ; Tropaeolum (amyloid mobilisation) ; Xyloglucan ; α-Xylosidase

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract The levels of cell-wall xyloglucan (amyloid) in nasturtium (Tropaeolum majus L.) cotyledons were monitored during a 28-d period covering seed imbibition, germination and early seedling development. The activities of the following enzymes capable of hydrolysing the glycosidic linkages in the xyloglucan were assayed in cotyledon extracts over the same period: endo-(1→4)-β-glucanase (EC 3.2.1.4), β-glucosidase (EC 3.2.1.21), α-xylosidase and β-galactosidase (EC 3.2.1.23). The endo-β-glucanase was assayed viscometrically using xyloglucan as substrate, and the three glycosidases using appropriate p-nitrophenylglycosides. Alpha xylosidase and β-galactosidase, the enzymes which would be expected to hydrolyse the side-chains from the xyloglucan molecule, were also assyed using xyloglucan as substrate. Under our culture conditions, xyloglucan levels remained constant at 30 mg per cotyledon pair for 7 d, that is until 3 d after germination: thereafter, the amount of xyloglucan diminished to zero in a 12-d period. The most rapid period of depletion was between days 9 and 13. The mobilisation of all reserve substances from the cotyledons resulted in a weight-loss of 92 mg: xyloglucan, therefore, is an important storage substance, representing 33% by weight of the seed's substrate reserves. It is a cell-wall storage polysaccharide. Xyloglucan mobilisation was accompanied by a 17-fold increase in endo-β-glucanase activity, a 7-fold increase in β-galactosidase and an 8-fold increase in α-xylosidase activities, all determined using xyloglucan as substrate. All three activities began to increase at day 5, peaked at days 12–14 when the most rapid phase of xyloglucan breakdown was over, and had declined to zero by days 22–25. The levels of theses enzymes have been shown to be consistent with their being responsible for xyloglucan hydrolysis in vivo. Nitrophenyl-β-galactosidase activity increased up to day 3, remained constant and then increased again 2.5-fold from day 5, peaking at day 11. Nitrophenyl-β-glucosidase remained relatively constant up to day 16 and then decreased to zero by day 25. Nitrophenyl-α-xylosidase activity was not detected.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00395907

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Substrate subsite recognition of the xyloglucan endo-transglycosylase or xyloglucan-specific endo-(1→4)-β-d-glucanase from the cotyledons of germinated nasturtium (Tropaeolum majus L.) seeds (1996)

Fanutti, Cristina ; Gidley, Michael J. ; Reid, J. S. Grant

Springer

Planta 200 (1996), S. 221-228

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ISSN: 1432-2048

Keywords: Cell wall (plant) ; Enzyme (specificity) ; Hemicellulose ; Tropaeolum ; Xyloglucan ; Xyloglucanendo-transglycosylase

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract We have investigated the substrate subsite recognition requirement of the xyloglucan endo-transglycosylase/xyloglucan-specific endo-(1→4)-β-d-glucanase (NXET) from the cotyledons of nasturtium seedlings. Seed xyloglucans are composed almost entirely of the Glc4 subunits XXXG, XLXG, XXLG and XLLG, where G represents an unsubstituted glucose residue, X a xylose-substituted glucose residue and L a galactosyl-xylose-substituted glucose residue. Thus in the xyloglucan sequence shown below, the xylose (Xyl) residues at the backbone glucose (Glc) residues numbered — 3,— 2, + 2 and + 3 may be galactose-substituted, and NXET cleaves between the unsubstituted glucose at — 1 and the xylose-substituted glucose at + 1, which never carries a galactosyl substituent. We have isolated the xyloglucan oligosaccharides XXXGXXXG and XLLGXLLG from NXET digests of tamarind seed xyloglucan, have modified them enzymatically using a pure xyloglucan oligosaccharide-specific α-xylosidase from nasturtium seeds to give GXXGXXXG and GLLGXLLG, and have identified and compared the products of NXET action on XXXGXXXG, GXXGXXXG, XLLGXLLG and GLLGXLLG. We have also compared the molar proportions of XXXG, XLXG, XXLG and XLLG in native tamarind and nasturtium seed xyloglucans with those in NXET digests of these polysaccharides. Using these and existing data we have demonstrated that NXET action does not require xylosesubstitution at glucose residues — 4, — 2, + 1 and + 3 and that xylose substitution at + 2, is a requirement. There may also be a requirement for xylose substitution at — 3. We have demonstrated also that galactosyl substitution of a xylose residue at + 1 prevents, and at — 2 modifies, chain-cleavage. A partial model for the minimum substrate binding requirement of NXET is proposed.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00208312

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