Interconversion and translocation of free sugars during galactomannan utilization in germinating guar (Cyamopsis tetragonoloba) seed

With the onset of the degradation of galactomannan, the galactose and mannose levels increased in the endosperm. The hydrolysis of galactomannan was more or less complete within the first 3 days of germination. In the cotyledons, sucrose was the predominant free sugar during the period of rapid galactomannan hydrolysis and reducing sugars (glucose + fructose) were present in only 10–20% proportion. The level of soluble acid invertase activity was in the order of embryonic axis > endosperm > cotyledons. On the basis of (a) absence of galactose and mannose, (b) high proportion of sucrose, (c) very fast conversion of [¹⁴C]glucose and [¹⁴C]mannose to [¹⁴C]sucrose and (d) very low levels of both soluble and bound invertases in cotyledons, we conclude that there is an active synthesis of sucrose in this tissue where disaccharide seems to be least hydrolysed during the period of galactomannan mobilization. A rapid hydrolysis of galactomannan in endosperm during early germination resulted in the synthesis of some starch, as a temporary reserve, in cotyledons. When the cotyledons entered the phase of first leaf formation, cotyledonary sucrose was hydrolysed giving rise to invert sugars. In the embryonic axis, the increase in the ratio of reducing sugars to sucrose coupled with a higher level of invertase, compared with sucrose-UDP glucosyl transferase, indicated that free sugars from the cotyledons are translocated to the embryonic axis as sucrose.     

THE ROLE OF THE ENDOSPERM IN THE GERMINATION OF LEGUMES: GALACTOMANNAN,NITROGEN, AND PHOSPHORUS CHANGES IN THE GERMINATION OF GUAR (CYAMOPSIS TETRAGONOLOBA; LEGUMINOSAE)

The endosperm of Cyamopsis tetragonoloba (“guar”) contains 41 % of the dry weight and 45 % of the acetone-insoluble-solids of the seed, but only 3–11 % of the nitrogen and phosphorus. At least 75 % of the acetone-insoluble-solids of the endosperm is galactomannan, only about 12% being accounted for as pentosan, pectin, protein, phytin, ash, and dilute-acid-insoluble residue. During a five-day germination period at 30 C, all of the galactomannan and all but 5 % of the dry weight of the endosperm disappeared, being translocated to the cotyledons. About ⅓ of the nitrogen and phosphorus of the endosperm plus seed coat were also translocated. After a 36-hr lag, the accumulation of the nitrogen and acetone-insoluble-solids in the seedling axis were linear, while the total dry weight and phosphorus showed a rapid increase followed by a slower accumulation during the five-day period. In the cotyledons, the dry weight temporarily increased, but the acetone-insoluble-solids, nitrogen and phosphorus showed only a net decrease after 84, 36 and 36 hr, respectively. Scanning election micrographs of dry-fractured and sectioned endosperm show that the bulk of the endosperm is a solid mass of galactomannan with essentially no cell lumina; a several-cell layer (“aleurone”) of thick-walled cells of similar structure is metabolically active.     

A dual rôle for the endosperm and its galactomannan reserves in the germinative physiology of fenugreek (Trigonella foenum-graecum L.), an endospermic leguminous seed

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.     

The mannan from Schizolobium parahybae endosperm is not a reserve polysaccharide

In higher plants, mannans are found as dominant reserve material in the endosperm of Arecaceae seeds and also in some species from Apiaceae, Rubiaceae and Asteraceae. A linear β(1 → 4)-d-mannan was now isolated from the endosperm of Schizolobium parahybae, family Caesalpiniaceae, a native of Southern Brazil. Its seeds were germinated and the consumption of polysaccharides from the endosperm, namely galactomannans and β(1 → 4)-d-mannan, was analysed at differents stages of germination. At the 6th day after germination no residual 3:1 Man:Gal galactomannan was found, indicating that complete degradation of galactomannan had been reached. However, after 12 days of germination, the mannan was recovered from the remaining endosperm. Its presence in the endosperm after germination demonstrated that it is not a reserve material as described for seeds of other species.     

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

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.     

Import of Sucrose and its Partitioning in the Synthesis of Galactomannan and Raffinose-oligosaccharides in the Developing Guar (Cyamopsis tetragonolobus) Seed

Import of sucrose and its transformation to galactomannan andraffinose-oligosaccharides have been studied in the developingguar seed. The amount of galactomannan gradually increased withthe ageing of the seed. During the entire period of pod development,sucrose constituted the major portion of the free sugars inthe seed (both endosperm and cotyledons) as well as in the podwall. Besides myo-inositol, the free sugars detected in thedeveloping endosperm and cotyledons were glucose, fructose,raffinose and stachyose. Some compounds, possibly glycosides(RG values higher than that of fructose), were also detectedin the endosperm. In the later stages of seed development, therelative proportion of raffinose in the free sugars increased,reaching 50% of the total free sugars in 77-d-old cotyledons.With pod maturity, the activities of soluble acid and boundacid invertases in the pod wall increased manifold with a concomitantdecline in the non-reducing sugar content. These enzymes seemto be involved in the mobilization of sucrose from this fruitingstructure into the seed. An increased synthesis of raffinose-oligosaccharidesboth in the endosperm and cotyledons was associated with highactivities of soluble acid invertase (pH 4.8) and sucrose-UDPglucosyl transferase in these tissues. Feeding uniformly labelled¹⁴C-sugars to the detached intact pods as well as to the isolatedendosperm and cotyledons resulted in labelling of all endogenousfree sugars and galactomannan. The uptake and incorporationinto galactomannan of ¹⁴C was stimulated by Co²⁺, Mn²⁺ and Mg²⁺.Except for mannose, a major proportion of the ¹⁴C from glucose,fructose and sucrose appeared in sucrose in both endosperm andcotyledons indicating a fast reconstitution of sucrose in situ.Based on the present results, a possible mode of transformationof sucrose to galactomannan and raffinose-oligosaccharides hasbeen proposed. Key words: Sucrose, galactomannan, raffinose-oligosaccharides, invertase, sucrose-UDP glucosyl transferase, ¹⁴C-incorporation, guar seed     

Effect of abscisic acid on galactomannan degradation and endo-β-mannanase activity in seeds of Sesbania virgata (Cav.) Pers. (Leguminosae)

Seeds of Sesbania virgata (Cav.) Pers. (Leguminosae) have an endosperm which accumulates galactomannan as a storage polysaccharide in the cell walls. After germination, it is hydrolysed by three enzymes: α-galactosidase (EC 3.2.1.22), endo-β-mannanase (EC 3.2.1.78) and β-mannosidase (EC 3.2.1.25). This work aimed at studying the effect of abscisic acid (ABA) on galactomannan degradation during and after germination. Seeds were imbibed in water or in 10⁻⁴ M ABA, and used to evaluate the effect of exogenous and endogenous ABA. Tissue printing was used to follow biochemical events by detecting and localising endo-β-mannanase in different tissues of the seed. The presence of exogenous ABA provoked a delay in the cellular disassembly of the endosperm and disappearance of endo-β-mannanase in the tissue. This led to a delay in galactomannan degradation. The testa (seed coat) of S. virgata contains endogenous ABA, which decreases ca. fourfold during storage mobilisation after germination, permitting the galactomannan degradation in the endosperm. Furthermore, endo-β-mannanase was immunolocalised in the testa, which has a living cell layer. The ABA appears to modulate storage mobilisation in the legume seed of S. virgata, and a cause–effect relationship between ABA (probably through testa) and activities of hydrolases is proposed.     

Composition, Degradation and Utilization of Endosperm During Germination in the Oil Palm (Elaeis guineensis Jacq.)

The insoluble carbohydrate and lipid fractions, and -D-galactosidase,ß-D-mannosidase and isocitrate lyase activities werestudied in the various tissues of oil palm (Elaeis guineensisJacq.) kernels prior to and during germination. In ungerminatedkernels insoluble carbohydrate and lipid constituted 36 and47% of endosperm dry weight respectively. During germinationthe thick endosperm cell walls became markedly thinner, concurrentwith a significant decrease in the percentage of insoluble carbohydrateand an increase in -galactosidase and ß-mannosidaseactivity in both degraded and residual endosperm. The proportionof lipid in degraded endosperm also increased significantly.The insoluble carbohydrate appears to be a galactomannan locatedin the secondary walls of the endosperm. No galactomannan wasdetected in oil palm embryos or haustoria. Isocitrate lyasewas present in, and confined to, tissues of the haustorium ofgerminating kernels. The enzyme was not active in endospermat any stage of germination, nor was it active in embryos beforeor at the end of imbibition. The results suggest that galactomannan is the second largestcomponent of oil palm endosperm and that it is utilized morerapidly than lipid during the early stages of germination. Thefact that isocitrate lyase activity is confined to the haustoriumsuggests that in Elaeis gluconeogenesis, the conversion of triglycerideto carbohydrate, takes place entirely within the cotyledon ofthe seed. Elaeis guineensis, galactomannan, galactosidase, germination, isocitrate lyase, mannosidase, oil palm     

The function of the aleurone layer during galactomannan mobilisation in germinating seeds of fenugreek (Trigonella foenum-graecum L.), crimson clover (Trifolium incarnatum L.) and lucerne (Medicago sativa L.): A correlative biochemical and ultrastructural study

Summary The reserve endosperm galactomannans of fenugreek (Trigonella foenum-graecum L.), crimson clover (Trifolium incarnatum L.) and lucerne (Medicago sativa L.) are broken down to free galactose and mannose in dry-isolated endosperms (devoid of embryo) incubated under germination conditions. Breakdown is prevented by inhibition of protein synthesis or of oxidative phosphorylation in the aleurone layer. Resting aleurone cells contain inter alia a large number of ribosomes more or less regularly distributed in the ground plasma. At the onset of germination, before galactomannan breakdown begins, polysomes are formed and seem, at least partly, to become associated with vesicles and flat cisternae both probably newly formed and derived from ER. Concurrently with galactomannan breakdown in the reserve cells, wall corrosion occurs in the aleurone layer, the contents of the aleurone grains disappear and the rough vesicles and cisternae proliferate. Later a large central vacuole is formed which incorporates smaller vacuoles emerging from the cytoplasm, and at the same time the rough ER vesicles and cisternae become highly distended.It is concluded that the cells of the aleurone layer are responsible for the synthesis and secretion into the storage cells of the enzymes necessary for galactomannan degradation. The physiology of galactomannan breakdown is compared and contrasted with that of starch mobilisation in the endosperm of germinating cereal grains.This is part three in a series of papers dealing with galactomannan metabolism. Part two: Planta (Berl.) 100, 131–142 (1971).     

The emergence of embryos from hard seeds is related to the structure of the cell walls of the micropylar endosperm, and not to endo-beta-mannanase activity

BACKGROUND AND AIMS: Seeds of carob, Chinese senna, date and fenugreek are hard due to thickened endosperm cell walls containing mannan polymers. How the radicle is able penetrate these thickened walls to complete seed germination is not clearly understood. The objective of this study was to determine if radicle emergence is related to the production of endo-beta-mannanase to weaken the mannan-rich cell walls of the surrounding endosperm region, and/or if the endosperm structure itself is such that it is weaker in the region through which the radicle must penetrate. METHODS: Activity of endo-beta-mannanase in the endosperm and embryo was measured using a gel assay during and following germination, and the structure of the endosperm in juxtaposition to the radicle, and surrounding the cotyledons was determined using fixation, sectioning and light microscopy. KEY RESULTS: The activity of endo-beta-mannanase, the major enzyme responsible for galactomannan cell wall weakening increased in activity only after emergence of the radicle from the seed. Thickened cell walls were present in the lateral endosperm in the hard-seeded species studied, but there was little to no thickening in the micropylar endosperm except in date seeds. In this species, a ring of thin cells was visible in the micropylar endosperm and surrounding an operculum which was pushed open by the expanding radicle to complete germination. CONCLUSIONS: The micropylar endosperm presents a lower physical constraint to the completion of germination than the lateral endosperm, and hence its structure is predisposed to permit radicle protrusion.     

Structure and biochemistry of endosperm breakdown in date palm (Phoenix dactylifera L.) seeds

Summary The zone of endosperm breakdown in the germinated date seed (Phoenix dactylifera L.) is a narrow area immediately adjacent to the surface of the enlarging cotyledon, or haustorium. The zone width is correlated with the amount of cell division in the adjacent region of the haustorium. The sequence of endosperm breakdown is: 1. protein bodies vacuolate, 2. storage cell walls become electron-transparent immediately adjacent to the protoplast of each endosperm cell, 3. all remaining cytoplasm and lipid bodies disappear, and 4. the remaining cell walls become electron-transparent and collapse against the haustorium surface. Two cell wall hydrolases are present—endo-mannanase (EC3.2.1.78) and -mannosidase (EC3.2.1.25). -mannosidase is detectable in the endosperm before germination. At germination, the major portion of activity is found in the softened endosperm. -mannanase is only detectable from germination and there is always hundreds of fold greater activity in the softened endosperm than elsewhere. Proteinase is detectable in trace amounts at germination in the softened endosperm but is also found in the haustorium at later stages. Isolated haustoria, incubated in extracted ivory nut (Phytelephas macrocarpa) mannan in buffer, cause no mannan breakdown. Haustoria, incubated in a solution of locust bean galactomannan, cause no decrease in galactomannan viscosity. Our observations suggest that although haustoria probably regulate mannan breakdown in the endosperm, they do not seem to secrete the hydrolytic enzymes concerned.     

Mobilisation of the major stored reserves in the embryo of fenugreek (Trigonella foenum-graecum L., Leguminosae), and correlated enzyme activities

Changes in total nitrogen, soluble amino nitrogen, lipid and phytate contents, and in the activities of proteinase (pH 7.0), isocitrate lyase and phytase were followed in the endosperm, cotyledons, and axis during germination of fenugreek seeds and subsequent growth of the seedlings. The endosperm is comprised largely of cell-wall galactomannans: the majority of the seed total nitrogen, lipid and phytate (5%, 8%, 0.44% of seed dry weight respectively) is localised within the cotyledons as stored reserves. Germination is completed after 10–14 h from the start of imbibition, but the major reserves are not mobilised during the first 24 h. Then the total nitrogen content of the cotyledons starts to decrease and that of the axis increases; there is a concomitant accumulation of soluble amino nitrogen in both cotyledons and axis. An increase in proteinase activity in the cotyledons correlates well with the depletion of total nitrogen therein. Depletion of lipid and phytate reserves in the different seed tissues constitutes a late event, occurring after 50 h from the start of imbibition, and is coincident with the final disintegration of the endosperm tissue. The depletion of phytate and stored lipids is accompanied by an increase in phytase and isocitrate lyase activity. It appears that the products of lipid hydrolysis are converted by gluconeogenesis to serve as the major source of sugars for the growing axis after the endosperm galactomannan has been completely mobilised.     

Testa is involved in the control of storage mobilisation in seeds of <Emphasis Type="Italic">Sesbania virgata</Emphasis> (Cav.) Pers., a tropical legume tree from of the Atlantic Forest

Seeds of Sesbania virgata (Cav.) Pers. (Leguminosae) contain galactomannan as a cell wall storage polysaccharide in the endosperm. After germination, it is hydrolysed by three enzymes: α-galactosidase (EC 3.2.1.22), endo-β-mannanase (EC 3.2.1.78) and β-mannosidase (EC 3.2.1.25). This work aimed at studying the role of the testa (seed coat) on galactomannan degradation during and after germination. Seeds were imbibed in water, with and without the testa, and used to evaluate the effect of this tissue on storage mobilisation, as well as its possible role in the galactomannan hydrolases activities. Immunocytochemistry and immunodotblots were used to follow biochemical events by detecting and localising endo-β-mannanase in different tissues of the seed. Endo-β-mannanase and α-galactosidase activities were found in the testa and latter in the endosperm during galactomannan degradation. The former enzyme was immunologically detected in the testa, mainly during germination. The absence of the testa during imbibition led to the anticipation of protein mobilisation and increased of the α-galactosidase activity and galactomannan degradation. Thus, the testa appears to play a role during storage mobilisation in the legume seed of S. virgata probably by participating in the control of the production, modification and/or storage of the hydrolases.     

Endo-[beta]-Mannanase Activity Present in Cell Wall Extracts of Lettuce Endosperm prior to Radicle Emergence

Lettuce (Lactuca sativa L.) endosperm cell walls isolated prior to radicle emergence underwent autohydrolysis, the rate of which was correlated with whether radicle emergence would subsequently occur. Extraction of endosperm cell walls with 6 M LiCl suppressed autohydrolysis, and the desalted extract possessed activity that was capable of hydrolyzing purified locust bean galactomannan but not arabinogalactan, carboxymethylcellulose, glucomannan, polygalacturonic acid, tomato galactomannan, or native lettuce endosperm cell walls. Some hydrolytic activity was detected on endosperm cell walls if they were modified by partial trifluoroacetic acid hydrolysis or pretreatment with guanidinium thiocyanate. In extended incubations the cell wall enzyme extract released only large molecular mass fragments from locust bean galactomannan, indicating primarily endo-activity. Galactomannan-hydrolyzing activity in the cell wall extract increased as a function of imbibition time and was greatest just prior to radicle emergence. Thermoinhibition (imbibition at 32[deg]C) or treatment with abscisic acid at a temperature optimal for germination (25[deg]C) suppressed both germination and endosperm cell wall mannanase activity, whereas alleviation of thermoinhibition with gibberellic acid was accompanied by significant enhancement of mannanase activity. We conclude that a cell wall-bound endo-[beta]-mannanase is expressed in lettuce endosperm prior to radicle emergence and is regulated by the same conditions that govern germination.     

Phytin is synthesized in the cotyledons of germinated castor-bean seeds in response to exogenously supplied phosphate

Following germination of the castor bean (Ricinus communis L.) seed, levels of phytin decline in both the endosperm and the embryo. However, as seedling growth continues, phytin increase in the latter to a level exceeding that present in the mature dry embryo, while phytin declines concomitantly in the endosperm. It is likely that phosphate mobilized from phytin in the endosperm acts as a substrate for phytin synthesis in the embryo. This is supported by the observation that isolated embryos supplied with phosphate accumulate phytin, particularly in the cotyledons. This increase is enhanced whenmyo-inositol is provided concurrently as a carbon source. Phytin synthesis in the cotyledons of the isolated embryos can occur without the attached axis. Whether initially exposed to exogenous phosphate or not, the isolated cotyledons remain competent in their ability to synthesize phytin for an extended post-germinative period, even though the major reserves are being mobilized at this time.     

d-Galactose Uptake by Fenugreek Cotyledons : Effect of Water Stress

The uptake of d-galactose was studied in detached fenugreek (Trigonella foenum-graecum L.) cotyledons. Uptake kinetics and treatment with p-chloromercury-benzenesulfonic acid indicated that at low concentrations d-galactose was taken up by a carrier. At higher concentrations a diffusion-like component existed. Proton flux and pH studies, treatment with α-naphthaleneacetic acid, and uptake experiments under water stress conditions suggested that d-galactose was not taken up via H⁺ contransport. However, d-galactose uptake was under metabolic control. Uptake kinetics under water stress conditions suggested that moderate water stress either increased the K_m of the carrier or decreased the V_max. However, prolonged stress transformed the carrier-mediated uptake into a diffusion uptake transport. The uptake of d-galactose by fenugreek cotyledons was very low before and just after germination, was maximum after 35 hours imbibition, and started decreasing thereafter. The different uptake rates of d-galactose with imbibition times were attributed to the operation of the carrier. At low uptake rates the carrier did not operate. Treatment with cycloheximide suggested that the carrier was synthesized de novo just after germination and stopped operating when all galactomannan hydrolysis was over. Results were discussed in the context of control of endosperm galactomannan hydrolysis by the cotyledons of fenugreek embryo.     

Enzymic activities and galactomannan mobilisation in germinating seeds of fenugreek (Trigonella fœnum-graecum L. Leguminosae)

Summary The activities of -galactosidase, -mannosidase and -mannosidase were determined in extracts from the endosperm and from the embryo of fenugreek seeds at different stages of germination. Endosperm homogenates contained little or no activity of the above enzymes in the early stages of germination, before the reserve galactomannan began to be mobilised. The onset of galactomannan breakdown coincided with the appearance of -galactosidase and -mannosidase activities, which increased throughout the period of galactomannan degradation and then remained constant. A similar rise in -galactosidase and -mannosidase activities occurred during galactomannan breakdown in dry-isolated endosperms incubated under germination conditions. The increase could be suppressed by metabolic inhibitors which also inhibit galactomannan breakdown. Embryo homogenates contained high -galactosidase, high -mannosidase and some -mannosidase activity at all stages of germination.No oligomannosyl -1,4 phosphorylase activity could be detected either in the endosperm or in the embryo.It is concluded that the galactomannan of fenugreek is broken down by a series of hydrolases secreted by the aleurone layer of the endosperm. They include -galactosidase, -mannosidase and probably also endo--mannanase.This is part four in a series of papers dealing with galactomannan metabolism. Part three: Planta (Berl.) 106, 44–60 (1972).     

Degradation of the endosperm cell walls of Lactuca sativa L., cv. Grand Rapids

The timing of mobilisation of lipid, sucrose, raffinose and phytate in lettuce seeds (achenes) (cv. Grand Rapids) has been examined. These reserves (33%, 1.5%, 0.7%, 1.4% of achene dry weight, respectively) are stored mostly in the cotyledons. Except for a slight degradation of raffinose and increase in sucrose, there is no detectable reserve mobilisation during germination. The endosperm (8% of seed dry weight), which has thick, mannan-containing cell walls (carbohydrate, 3,4% of seed dry weight), is completely degraded within about 15h following germination. Mannanase activity increases about 100-fold during the same period and arises in all regions of the endosperm. Also during this period sucrose and raffinose are degraded and fructose and glucose accumulate in the embryo. The endosperm hydrolysis products are taken up by the embryo, and are probably used as an additional reserve to support early seedling growth. However, endosperm cell-wall carbohydrates, such as mannose, are not found as free sugars. Lipid and phytate are degraded in a later, second phase of mobilisation. Low levels of sucrose are present in the embryo, mostly in the cotyledons, and large amounts of fractose and glucose (14% of seedling dry weight at 3 days after sowing) accumulate in the hypocotyl and radicle. It is suggested that sucrose, produced in the cotyledons by gluco-neogenesis, is translocated to the axis and converted there to fructose and glucose.