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  • 1
    Electronic Resource
    Electronic Resource
    A dual rôle for the endosperm and its galactomannan reserves in the germinative physiology of fenugreek (Trigonella foenum-graecum L.), an endospermic leguminous seed (1979)
    Springer
    Planta 147 (1979), S. 145-150 
    Details
    ISSN: 1432-2048
    Keywords: Endosperm ; Galactomannan ; Germination (seeds) ; Storage polysaccharide ; Trigonella ; Water potential
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Some 30% of the reserve material in the fenugreek seed is galactomannan localised in the endosperm; the remainder is mainly protein and lipid in the cotyledons of the embryo. The importance of galactomannan to the germinative physiology of fenugreek has been investigated by comparing intact and endosperm-free seeds. From a purely nutritional point of view the galactomannan's rôle is not qualitatively different from that of the food reserves in the embryo. Nevertheless, due to its spatial location and its hydrophilic properties, the galactomannan is the molecular basis of a mechanism whereby the endosperm imbibes a large quantity of water during seed hydration and is able to “buffer” the germinating embryo against desiccation during subsequent periods of drought-stress. The galactomannan is clearly a dual-purpose polysaccharide, regulating water-balance during germination and serving as a substrate reserve for the developing seedling following germination. The relative importance of these two rôles is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00389515
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  • 2
    Electronic Resource
    Electronic Resource
    Galactomannan formation and guanosine 5′-diphosphate-mannose: galactomannan mannosyltransferase in developing seeds of fenugreek (Trigonella foenum-graecum L., leguminosae) (1982)
    Springer
    Planta 155 (1982), S. 105-111 
    Details
    ISSN: 1432-2048
    Keywords: Galactomannan ; Endosperm ; Polysaccharide (biosynthesis, storage) ; Mannosyltransferase ; Seed (development) ; Trigonella
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The time-course of galactomannan and stachyose (digalactosyl-sucrose) deposition in the fenugreek seed endosperm has been determined, and correlated with standard parameters of seed development. During, and only during, the period of galactomannan deposition, endosperm homogenates are capable of catalysing the transfer of labelled d-mannosyl residues from guanosine 5′-diphosphate d-[U-14C]mannose to a soluble polysaccharide product indistinguishable from galactomannan. The mannosyltransferase activity peaks twice, once at the beginning of galactomannan deposition, and again in the middle of the most rapid phase of galactomannan deposition. The enzyme in the later peak sediments with grossly particulate material (1,000 g pellet), whereas the earlier peak contains a considerable proportion of a particulate enzyme sedimenting at 100,000 g. These observations are discussed in the light of existing information on the ultrastructural aspects of galactomannan deposition. The mannosyltransferase is clearly involved in galactomannan formation in vivo, but the status of an accompanying galactosyltransferase is less clear.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00392539
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  • 3
    Electronic Resource
    Electronic Resource
    Enzyme specificity in galactomannan biosynthesis (1995)
    Springer
    Planta 195 (1995), S. 489-495 
    Details
    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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  • 4
    Electronic Resource
    Electronic Resource
    Morphological aspects of the galactomannan formation in the endosperm ofTrigonella foenum-graecum L. (Leguminosae) (1977)
    Springer
    Planta 133 (1977), S. 243-248 
    Details
    ISSN: 1432-2048
    Keywords: Endosperm ; Galactomannan ; Secretion ; Ultrastructure ; Trigonella
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The mode of deposition (secretion) of galactomannan in the cells of the seed endosperm ofTrigonella foenum-graecum has been studied by electron microscopy. In cells which are just beginning to secrete galactomannan there are stacks of rough endoplasmic reticulum (ER). The intracisternal space (containing the enchylema) of the rough ER then swells, becomes vacuolated and forms a voluminous network, with “pockets” of cytoplasm entrapped within poculiform rough ER. The enchylema contains material which reacts with periodate-thiocarbohydrazidesilver proteinate in a very similar manner to the galactomannan already deposited in the cell wall. It appears that the galactomannan is formed in the intracisternal space of the rough endoplasmic reticulum and then expelled outside the plasmalemma. This mode of deposition contrasts with that of other plant cell wall polysaccharides whose secretion is mediated by Golgi vesicles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00380684
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  • 5
    Electronic Resource
    Electronic Resource
    Endo-β-mannanase, the leguminous aleurone layer and the storage galactomannan in germinating seeds ofTrigonella foenum-graecum L. (1977)
    Springer
    Planta 133 (1977), S. 219-222 
    Details
    ISSN: 1432-2048
    Keywords: Aleurone layer ; Endo-β-mannanase ; Endosperm ; Galactomannan ; Germination ; Leguminous seeds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The activity ofendo-β-mannanase in the endosperm of fenugreek seeds at different stages of germination varies pari passu with storage galactomannan breakdown.Endo-β-mannanase is similarly associated with the galactomannan breakdown which occurs when isolated fenugreek half-endosperms are incubated under “germination” conditions. Metabolic inhibitors,acting on the aleurone layer reduceendo-β-mannanase production in the half-endosperms in proportion to their inhibition of galactomannan breakdown. It is concluded (a) thatendo-β-mannanase activity, like galactomannan breakdown, is regulated by the fenugreek aleurone layer and (b) that theendo-β-mannanase is almost certainly instrumental in bringing about galactomannanan hydrolysis in vivo.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00380680
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  • 6
    Electronic Resource
    Electronic Resource
    Regulation of α-galactosidase activity and the hydrolysis of galactomannan in the endosperm of the fenugreek (Trigonella foenum-graecum L.) seed (1985)
    Springer
    Planta 166 (1985), S. 271-275 
    Details
    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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