普甜玉米种子萌发期糖代谢和水解酶活性动态变化

种子萌发是一个较复杂的生理生化过程,是种子贮藏物质在酶的作用下经过一系列反应生成蔗糖、葡萄糖、果糖等各种糖类化合物,为种子萌发提供碳源和能量。该研究利用两个不同来源、籽粒营养成分具有差异的普甜玉米种子动态分析了种子萌发期蔗糖、果糖和葡萄糖代谢及关键水解酶活性的变化。结果表明:在种子萌发过程中,E22和T26两个普甜玉米种子的物质动员量、物质利用率、蔗糖、葡萄糖和果糖含量均存在遗传差异,其中淀粉含量较高的T26种子具有较突出的物质利用率,表明淀粉是影响普通甜玉米种子萌发的关键因子;在种子萌发4~8 d、6~10 d时,E22分别具有较高的蔗糖和葡萄糖含量,而T26是在萌发10 d时具有较高的果糖含量。随着种子发芽进程,蔗糖合成酶活性、淀粉酶活性都呈逐渐上升的趋势,但淀粉酶活性变幅较明显;进一步关联分析8个种子萌发物质利用性状间关系,结果表明种子萌发期间,种子物质动员量主要受淀粉酶活性影响,而种子物质利用率则主要受糖含量多少制约。因此,提高甜玉米种子萌发期物质利用率对其种子发芽和幼苗生长,增强其与杂草生长的竞争力,提高甜玉米产量均具有重要意义。     

Dynamics of carbohydrates in the embryo axes of horse chestnut seeds during their transition from dormancy to germination

It was shown that the content of carbohydrates and their composition in embryo axes of horse chestnut seeds changed as seeds acquired a capability of dormancy release and germination. Sucrose prevailed among carbohydrates, comprising to 150–160 mg/g dry wt. During the first half of the seed imbibition time, oligosaccharides, namely raffinose and stachyose, degraded, whereas the contents of glucose and fructose were very low. The second half of the imbibition period (until radicle protrusion) was characterized by a cessation of oligosaccharide breakdown and accumulation of monosaccharides. Carbohydrate balance showed that the contribution of oligosaccharide breakdown to sucrose and monosaccharide accumulation was rather small, and monosaccharides accumulated mostly at the expense of sucrose gradually coming from cotyledons during imbibition. The trend of carbohydrate metabolism in imbibing axial organs was similar during the entire period of a seed dormancy release in the course of stratification. A readiness for the commencement of these processes during the entire dormancy period implies that carbohydrate conversions in embryo axes are not a trigger for a dormancy release. Monosaccharide accumulation in embryo axes before radicle protrusion produces an increase in the osmotic pressure, as compared to that provided by sucrose, by approximately 20%. Recalcitrance of the horse chestnut seeds is discussed in relation to the role of carbohydrates and other endogenous osmotica in the establishment of osmotic properties.     

Effects of exogenous abscisic acid on leaf carbohydrate metabolism during cucumber seedling dehydration

Cucumber (Cucumis sativus L.) seeds were pretreated with exogenous abscisic acid (ABA) prior to germination. After germination, seedlings with three leaves were exposed to gradual dehydration. The effects of ABA on photosynthetic rate (Pn), daily water loss (WL) and water utilization efficiency (WUE) during dehydration were investigated, in addition to the variation of carbohydrates in leaves. ABA improved the Pn, WL and WUE of cucumber seedlings during dehydration. After rehydration, the seedlings pretreated with ABA showed a higher recovery in Pn, WL and WUE, as compared to those without an ABA pretreatment. Subsequent to dehydration, concentration of stachyose, raffinose, sucrose, glucose, and fructose increased in seedlings pretreated with ABA. Dehydration altered the proportions of the sugars in the total carbohydrates, and accelerated the accumulation of stachyose, raffinose and sucrose. After rehydration, carbohydrate concentrations of seedlings pretreated with ABA recovered to levels observed prior to dehydration. These results demonstrated that pretreatment of seeds with exogenous ABA enhanced carbohydrate tolerance to dehydration of cucumber seedlings.     

Changes in concentrations of soluble carbohydrates during germination of <Emphasis Type="Italic">Amaranthus caudatus</Emphasis> L. seeds in relation to ethylene,gibberellin A<Subscript>3</Subscript> and methyl jasmonate

Unimbibed Amaranthus caudatus seeds were found to contain stachyose, raffinose, verbascose, sucrose, galactinol, myo-inositol, glucose and fructose, while no galactose, maltose and maltotriose was detected. During imbibition, seed concentrations of verbascose, stachyose, raffinose, galactinol, myo-inositol (temporary) and fructose (transient) were observed to decrease; concentrations of galactose and maltose remained fairly constant, while those of sucrose, glucose and maltotriose increased, the increase in sucrose concentration was only temporary. Effects of gibberellin A₃ (GA₃) at 3 × 10⁻⁴ M and ethephon at 3 × 10⁻⁴ M alone or in the presence of methyl jasmonate (Me-JA) at 10⁻³ M on concentrations of soluble sugars during germination of A. caudatus seeds were examined. Me-JA was found to inhibit seed germination and fresh weight of the seeds, but did not affect sucrose, myo-inositol, galactose and maltose concentrations during imbibition for up to 20 h. The exogenously applied GA₃ was observed to enhance germination, stachyose breakdown and glucose concentration after 20 h of incubation. Ethephon stimulated seed germination as well as utilisation of stachyose, galactinol (both after 14 and 20 h) and raffinose (after 14 h of incubation). Although the stimulatory effect of either GA₃ or ethephon on seed germination was blocked by Me-JA; these stimulators increased mobilisation of raffinose and stachyose, but only ethephon enhanced both glucose and fructose after 14 and/or 20 h of incubation in the presence of Me-JA. The maltose concentration was increased by both GA₃ and ethephon alone and in the presence of Me-JA. Of the growth regulators studied, ethephon alone and/or in combination with Me-JA significantly increased the concentrations of glucose, fructose, galactose, maltose and maltotriose. The differences in sugar metabolism appear to be linked to ethylene or GA₃ applied simultaneously with Me-JA.     

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.     

Anaerobic carbohydrate metabolism in wheat and barley, two anoxia-intolerant cereal seeds

Cereals such as barley and wheat are unable to germinate underanoxic conditions. Data are presented on the utilization ofthe soluble sugars present in the dry seed of wheat and barleykept under strict anoxia, together with the status of the enzymesinvolved in the metabolism of carbohydrates. The amount of glucose, fructose, and sucrose decreases duringthe anaerobic treatment, indicating that carbohydrate metabolismtakes place in the seeds of wheat and barley kept under anoxicconditions. The analysis of the enzymes involved in the metabolism of carbohydratesshows that the enzymatic set needed to convert sucrose, glucose,and fructose to glucose-6P is present in the anaerobic seeds.Sucrose degradation seemingly occurs through a sucrose synthasepathway with nucleoside diphosphate kinase involved in the cyclingof urydilates. However, the activity of sucrose synthase, glucokinase,and fructokinase, all strongly induced in rice, an anoxia-tolerantcereal, are almost unaffected or even depressed in the two cerealseeds under investigation. The comparison of the results obtained and described in thispaper with the published data on the metabolism of carbohydratesin rice, indicate that the anoxia-intolerant species would rapidlysuffer and eventually die from sugar starvation if kept underanoxia for a relatively prolonged length of time (4–8d). Key words: Anoxia, cereal seed, carbohydrate metabolism     

Carbohydrates in the hypothallus and areolae of the crustose lichen <Emphasis Type="Italic">Rhizocarpon geographicum</Emphasis> (L.) DC.

Carbohydrate concentrations in the marginal hypothallus and areolae of the crustose lichen Rhizocarpon geographicum (L.) DC. were measured in north Wales, U.K. using gas chromatography. Ribitol, arabitol, and mannitol were the most abundant carbohydrates while α- glucose β-glucose, fructose, sucrose, and trehalose were present in smaller amounts. The concentrations of arabitol, ribitol, mannitol, fructose, and α-glucose were greater in the areolae while the concentration of trehalose was greater in the hypothallus. Concentrations of carbohydrates varied little between sample days. Concentrations of polyols in the hypothallus were not correlated with those in the areolae. These results suggest: 1) the hypothallus has a lower demand for carbohydrates than the areolae or there is limited transport from areolae to hypothallus, 2) increased trehalose in the non-lichenised hypothallus may be an adaptation to withstand stress and desiccation, and 3) polyols are partitioned differently in the hypothallus and areolae.     

Effect of Carbohydrate Demand on the Remobilization of Starch in Stolons and Roots of White Clover (Trifolium repens L.) after Defoliation

White clover plants were grown from stolon tips in growth cabinetsand then defoliated. Thereafter, changes in the contents ofnon-structural carbohydrates such as starch, sucrose, glucose,fructose, maltose, and pinitol in stolons and roots were monitored.Initial contents of carbohydrate reserves, photosynthetic supplyof new carbohydrates and carbohydrate demand after defoliationwere varied by growing the plants at various CO₂ partial pressures,by varying the extent of defoliation and by removing eitherroots or stolon tips at the time of defoliation. Remobilization of carbohydrate reserves in stolons increasedproportionally to their initial contents and was greater whenplants had been severely defoliated, suggesting that carbohydrateswere remobilized according to availability and demand. Starchwas the predominant reserve carbohydrate. Starch degradationwas associated with decreased contents of sucrose, glucose andfructose in young stolon parts and roots but not in old stolonparts suggesting that starch degradation was not strictly controlledby the contents of these sugars. A decrease in the demand forcarbohydrates by removal of roots did not decrease starch degradationbut increased the contents of sucrose, glucose, and fructose.Removal of stolon tips decreased starch degradation and contentsof sucrose, glucose, and fructose. The results suggest thatstarch degradation was controlled by a factor other than sucrose,glucose, and fructose which was exported from stolon tips, e.g.gibberellin. Key words: White clover, storage carbohydrates, remobilization, regrowth     

Early carbon mobilization and radicle protrusion in maize germination

Considerable amounts of information is available on the complex carbohydrates that are mobilized and utilized by the seed to support early seedling development. These events occur after radicle has protruded from the seed. However, scarce information is available on the role of the endogenous soluble carbohydrates from the embryo in the first hours of germination. The present work analysed how the soluble carbohydrate reserves in isolated maize embryos are mobilized during 6-24 h of water imbibition, an interval that exclusively embraces the first two phases of the germination process. It was found that sucrose constitutes a very significant reserve in the scutellum and that it is efficiently consumed during the time in which the adjacent embryo axis is engaged in an active metabolism. Sucrose transporter was immunolocalized in the scutellum and in vascular elements. In parallel, a cell-wall invertase activity, which hydrolyses sucrose, developed in the embryo axis, which favoured higher glucose uptake. Sucrose and hexose transporters were active in the embryo tissues, together with the plasma membrane H(+)-ATPase, which was localized in all embryo regions involved in both nutrient transport and active cell elongation to support radicle extension. It is proposed that, during the initial maize germination phases, a net flow of sucrose takes place from the scutellum towards the embryo axis and regions that undergo elongation. During radicle extension, sucrose and hexose transporters, as well as H(+)-ATPase, become the fundamental proteins that orchestrate the transport of nutrients required for successful germination.     

Carbohydrate Composition and Acid Invertase Activity in Rice Leaves Infected with Pyricularia oryzae

Ethanol-soluble carbohydrates in healthy and blast-infected leaves and also cultures of Pyricularia oryzae were analyzed using gas chromatography. Arabitol, mannitol, and trehalose occurred in infected leaf tissue, but not in healthy controls. Cultures of P. oryzae contained mannitol and trehalose, but not arabitol and sucrose. The presence of arabitol only in blast-infected rice leaves suggests that arabitol synthesis may be induced in infected leaf tissue as a result of the rice-blast fungus interaction, but may not be within blast fungus itself. The amounts of glucose, fructose, and sucrose in infected leaves were slightly increased until 5 days, and greatly enhanced at 7 days after inoculation, There were no differences in amounts of these sugars between the cultivars Nakdong and Dobong. At 7 days after inoculation, increases in amounts of arabitol, mannitol, and trehalose were pronounced in the susceptible cultivar Nakdong than in the moderately susceptible cultivar Dobong. The increased amounts of glucose and fructose in infected plants of the two cultivars were closely correlated with the presence of a very active invertase.     

八棱海棠种子超低温保存中含水量对糖代谢的影响

含水量是影响种子超低温保存效果的关键因素，而其作用机制尚不完全清楚。为探讨含水量对种子超低温保存生活力的影响途径，该研究以八棱海棠种子为材料，通过硅胶干燥法获得不同含水量的种子，测定超低温保存后种子生活力、糖含量及相关酶指标的变化并分析相关性。结果表明：(1)超低温保存15 d后，不同含水量种子生活力不同，随着种子含水量的降低，种子生活力呈现先升高后降低的趋势，含水量为9.02%的八棱海棠种子生活力最高，为53.33%;超低温保存120 d后，种子生活力随着含水量下降一直升高，含水量为6.40%生活力最高，为27.78%。这表明八棱海棠种子含水量对超低温保存后的生活力有明显影响，但受液氮保存时间影响，随着液氮保存时间的延长，最适含水量降低。(2)相关分析显示，超低温保存后种子含水量与生活力呈极显著负相关(r=-0.82);与果糖和蔗糖含量、酸性转化酶、果糖激酶呈显著负相关，而种子萌发率与这些指标呈显著正相关。这表明种子含水量通过影响酸性转化酶活性而影响蔗糖和果糖含量，进而影响蔗糖代谢，响应低温和脱水胁迫，最终导致生活力差异。种子生活力还受到介导果糖激酶的果糖代谢影响。此外，海藻糖也是种...     

Changes in germination, growth and soluble sugar contents of Sorghum bicolor (L.) Moench seeds under various abiotic stresses

The effect of various abiotic stresses on germination rate, growth and soluble sugar content in Sorghum bicolor (L.) Moench cv. CSH 6 seed embryos and endosperm during early germination was investigated. Under stress conditions germination, water potential and tissue water content decreased markedly. Subsequently, this reduction resulted in marked decreases in fresh weight both in embryos and endosperm. Conversely, a substantial increase in dry weight was observed. Furthermore, a considerable increase in the sugar contents in both embryo and endosperm was detected. The fructose level was always higher than glucose and sucrose in response to various stresses. However, as compared to the control the level of glucose and sucrose was higher in embryos and endosperm after stress treatments. Based upon these results a possible physiological role of sugars in the germination of sorghum seeds is discussed.     

Changes in soluble carbohydrates and starch amounts during somatic and zygotic embryogenesis of Acca sellowiana (Myrtaceae)

Comparative analysis of zygotic and somatic embryogenesis of Acca sellowiana showed higher amounts of sucrose, fructose, raffinose, and myo-inositol in zygotic embryos at different developmental stages than in corresponding somatic ones. These differences were mostly constant. In general, glucose levels were significantly lower than the other soluble carbohydrates analyzed, showing minor variation in each embryo stage. Despite the presence of sucrose in the culture medium, its levels conspicuously diminished in somatic embryos compared with the zygotic ones. Raffinose enhanced parallel to embryo development, regardless of its zygotic or somatic origin. Analysis of the soluble carbohydrate composition of mature zygotic cotyledon used as explant pointed out fructose, glucose, myo-inositol, sucrose, and raffinose as the most important. Similar composition was also found in the corresponding somatic cotyledon. Total soluble carbohydrates varied inversely, decreasing in zygotic embryos and increasing in somatic embryos until the 24th d, at which time they increased rapidly about sixfold in zygotic embryos until the 27th d, a period coinciding with the zygotic proembryos formation. Such condition seems to reflect directly the variation of endogenous sucrose level, mainly because glucose and fructose diminished continuously during this time period. This means that, in terms of soluble sugars, zygotic embryo formation occurred under a situation represented by high sucrose amounts, simultaneously with low fructose and glucose levels, while in contrast, somatic embryo formation took place under an endogenous sugar status characterized by a substantial fructose enhancement. Starch levels increased continuously in zygotic embryos and decreased in somatic ones, the reverse to what was found in fructose variation. Starch accumulation was significantly higher in somatic torpedo and cotyledonary embryos than in the corresponding zygotic ones.     

Changes in the activities of carbon metabolizing enzymes with pod development in lentil (<Emphasis Type="Italic">Lens culinaris</Emphasis> L.)

Activities of some key enzymes of carbon metabolism sucrose synthase, acid and alkaline invertase, phosphoenol pyruvate carboxylase, malic enzyme and isocitrate dehydrogenase were investigated in relation to the carbohydrate status in lentil pods. Sucrose remained the dominant soluble sugar in the pod wall and seed, with hexoses (glucose and fructose) present at significantly lower levels. Sucrose synthase is the predominant sucrolytic enzyme in the developing seeds of lentil (Lens culinaris L.). Acid invertase was associated with pod elongation and showed little activity in seeds. Sucrose breakdown was dominated by alkaline invertase during the development of podwall, while both the sucrose synthase and alkaline invertase were active in the branch of inflorescence. A substantial increase of sucrolytic enzymes was observed at the time of maximum seed filling stage (10–20 DAF) in lentil seed. The pattern of activity of sucrose synthase highly paralleled the phase of rapid seed filling and therefore, can be correlated with seed sink strength. It seems likely that the fruiting structures of lentil utilize phosphoenol pyruvate carboxylase for recapturing respired carbon dioxide. Higher activities of isocitrate dehydrogenase and malic enzyme in the seed at the time of rapid seed filling could be effectively linked to the deposition of protein reserves.     

Carbohydrates as regulatory factors on the rooting of <Emphasis Type="Italic">Eucalyptus saligna</Emphasis> Smith and <Emphasis Type="Italic">Eucalyptus globulus</Emphasis> Labill

Comparisons between related species with different rooting capacities can provide insights into the mechanisms controlling adventitious root development. The availability of carbohydrates is often considered exclusively as an energetic requirement to drive root development; the major regulatory role in the process is often attributed to phytohormones, particularly auxin. The roles of light quantity (irradiance) and carbohydrate supply available to young aseptic donor-plants on the adventitious rooting response of Eucalyptus globulus (rooting recalcitrant) and Eucalyptus saligna (easy-to-root) were examined. The effects of the type of carbohydrate supply (sucrose or glucose) on the rooting response of cuttings was also evaluated. Light intensity supplied to mother-plants (30 or 60 mol m^–2 s^–1) had limited influence on the rooting response of both species, whereas dark periods were detrimental, particularly for E. globulus. In E. globulus, rooting was promoted by the absence of sucrose in donor-plant media. Presence of sucrose in donor plant medium promoted root number but did not affect rooting percentage of E. saligna. A positive effect of glucose on cutting rhizogenesis was found if this hexose was supplied during the root induction phase, followed by sucrose in the root formation step, especially for E. globulus. The same effect was not seen with fructose. The beneficial effect of glucose in the induction phase on root number was also evident under suboptimal auxin concentrations.     

Hormone and sugar effects on rice sucrose transporter <Emphasis Type="Italic">OsSUT1</Emphasis> expression in germinating embryos

The rice (Oryza sativa L.) OsSUT1 gene encodes a sucrose transporter protein. OsSUT1 was suggested to contribute to phloem loading of sucrose. OsSUT1 expression is highly induced in embryos after seeds were imbibed in water and peaked at 2 days after imbibition, but mRNA levels decline gradually afterwards. In this study, we demonstrated that phytohormones and sugars regulate OsSUT1 expression. Antagonism of abscisic acid and gibberellic acid appeared to play an important role in regulating OsSUT1 expression during embryo germination. In addition, our data showed a glucose and sucrose effect on OsSUT1 expression that represented a bi-phase process. Initially, glucose and sucrose functioned as negative regulators of OsSUT1 expression in germinating embryos after a 1-day treatment; however, when the treatment duration was extended to 5 days, OsSUT1 expression was significantly enhanced. Therefore, we hypothesized that the glucose and sucrose effect might occur in combination with other side effects, such as changes in hormone content or catabolism. Based on the effects that sugar analogs have on OsSUT1 expression, we suggest that the signal transduction for regulating glucose-responsive OsSUT1 expression in embryos occurs via a hexokinase-mediated pathway.     

Effects of low temperature on growth and non-structural carbohydrates of the imperial bromeliad <Emphasis Type="Italic">Alcantarea imperialis</Emphasis> cultured in vitro

The imperial bromeliad Alcantarea imperialis grows naturally on rocky outcrops (‘inselbergs’) in regions where daily temperatures vary from 5 to 40°C. As carbohydrate metabolism is altered in response to cold, it could lead to reprogramming of the metabolic machinery including the increase in levels of metabolites that function as osmolytes, compatible solutes, or energy sources in order to maintain plant homeostasis. The aim of this study was to evaluate the effects of different temperatures on plant growth and non-structural carbohydrates in plants of A. imperialis adapted to low temperature. Seedlings of A. imperialis were grown in vitro under a 12-h photoperiod with four different day/night temperature cycles: 5/5°C, 15/15°C, 15/30°C (dark/light) and 30/30°C. Plants were also cultivated at 26°C in ex vitro conditions for comparison. The results showed an inverse relationship between temperature and germination time and no differences in the percentage of germination. Plants maintained for 9 months at 15°C presented a reduced number of leaves and roots, and a dry mass four times lower than plants grown at 30°C. Sugar content was higher in plants grown at 15°C than at 30°C. However, the highest amount of total sugar was found in plants growing under warm day/cold night conditions. Myo-inositol, glucose, fructose and sucrose were found predominantly under high temperatures, while under low temperatures, sucrose was apparently replaced by trehalose, raffinose and stachyose. Starch content was highest in plants grown under high temperatures. The lowest starch content was detected under low temperatures, suggesting its conversion into soluble carbohydrates to protect the plants against cold. These results indicated that low temperature retarded growth of A. imperialis and increased sugar levels, mainly trehalose, thus suggesting that these sugar compounds could be involved in cold tolerance.     

The Production of Bacillus cereus Enterotoxins Is Influenced by Carbohydrate and Growth Rate

Enterotoxin production is a key factor in Bacillus cereus food poisoning. Herein, the effect of the growth rate (μ) on B. cereus toxin production when grown on sucrose was studied and the Hemolytic BL enterotoxin (HBL) and nonhemolytic enterotoxin (Nhe) production by B. cereus was compared according to carbohydrate at μ = 0.2 h⁻¹. The anaerobic growth was carried out on continuous cultures in synthetic medium supplemented with glucose, fructose, sucrose, or an equimolar mixture of glucose and fructose. Concerning the HBL and Nhe enterotoxin production: (1) the highest enterotoxin production has occurred at μ = 0.2 h⁻¹ when growing on sucrose; (2) HBL production was repressed when glucose was consumed and the presence of fructose (alone or in mixture) cancelled glucose catabolite repression; (3) the consumption of sucrose increased Nhe production, which was not affected by the catabolite repression. Furthermore, analysis of the fermentative metabolism showed that whatever the μ or the carbon source, B. cereus used the mixed acid fermentation to ferment the different carbohydrates. The enterotoxin productions by this strain at μ = 0.2 h⁻¹ are highly influenced by the carbohydrates that do not involve any fermentative metabolism changes.     

Enzymic mechanism of starch breakdown in germinating rice seeds I. An analytical study

Time-sequence analyses of carbohydrate breakdown in germinating rice seeds shows that a rapid breakdown of starch reserve in endosperm starts after about 4 days of germination. Although the major soluble carbohydrate in the dry seed is sucrose, a marked increase in the production of glucose and maltooligosaccharides accompanies the breakdown of starch. Maltotriose was found to constitute the greatest portion of the oligosaccharides throughout the germination stage. α-Amylase activities were found to parallel the pattern of starch breakdown. Assays for phosphorylase activity showed that this enzyme may account for much smaller amounts of starch breakdown per grain, as compared to the amounts hydrolyzed by α-amylase. There was a transient decline in the content of sucrose in the initial 4 days of seed germination, followed by the gradual increase in later germination stages. During the entire germination stage, sucrose synthetase activity was not detected in the endosperm, although appreciable enzyme activity was present in the growing shoot tissues as well as in the frozen rice seeds harvested at the mid-milky stage. We propose the predominant formation of glucose from starch reserves in the endosperm by the action of α-amylase and accompanying hydrolytic enzyme(s) and that this sugar is eventually mobilized to the growing tissues, shoots or roots.