Carbohydrate metabolism during fruit development in sweet pepper (Capsicum annuum) plants

Growth, accumulation of sugars and starch, and the activity of enzymes involved in sucrose mobilization were determined throughout the development of sweet pepper fruits. Fruit development was roughly divided into three phases: (1) an initial phase with high relative growth rate and hexose accumulation, (2) a phase with declining growth rate and accumulation of sucrose and starch, and (3) a ripening phase with no further fresh weight increase and with accumulation of hexoses, while sucrose and starch were degraded. Acid and neutral invertase (EC 3.2.1.26) were closely correlated to relative growth rate until ripening and inversly correlated to the accumulation of sucrose. Acid invertase specifically increased during ripening, concurrently with the accumulation of hexoses. Sucrose synthase (EC 2.4.1.13) showed little correlation to fruit development, and in periods of rapid growth the activity of sucrose synthase was low compared to the invertases. However, during late fruit growth sucose synthase was more active than the invertases. We conclude that invertase activities determine the accumulation of assimilates in the very young fruits, and a reactivation of acid invertase is responsible for the accumulation of hexoses during ripening. During late fruit growth, before ripening, sucrose synthase is transiently responsible for the sucrose breakdown in the fruit tissue. Results also indicate that pyrophosphate-dependent phosphofructokinase (EC 2.7.1.90) and its activator fructose-2,6-bisphosphate (Fru2,6bisP) are involved in the regulation of the sink metabolism of the fruit tissue.     

Sucrose Metabolism in Tubers of Potato (Solanum tuberosum L.): Effects of Sink Removal and Sucrose Flux on Sucrose-Degrading Enzymes

Excision of developing potato (Solanum tuberosum L.) tubers from the mother plant, followed by storage at 10°C, resulted in a rapid, substantial decrease in sucrose synthase activity and considerable increases in hexose content and acid invertase activity. A comparison of the response of three genotypes, known to accumulate different quantities of hexoses in storage, showed that both sucrose synthase activity and the extent to which activity declined following excision were similar in all cases. However, there was significant genotypic variation in the extent to which acid invertase activity developed, with tubers accumulating the highest hexose content also developing the highest extractable activity of invertase. Similar effects were found in nondetached tubers when growing plants were maintained in total darkness for a prolonged period. Furthermore, supplying sucrose to detached tubers through the cut stolon surface prevented the decline in sucrose synthase activity. Maltose proved to be ineffective. Western blots using antibodies raised against maize sucrose synthase showed that the decline in sucrose synthase activity was associated with the loss of protein rather than the effect of endogenous inhibitors. Although there were indications that maintaining a flux of sucrose into isolated tubers could prevent the increase in acid invertase activity, the results were not conclusive.     

Sink development, sucrose metabolising enzymes and carbohydrate status in turnip (Brassica rapa L.)

Accumulation of 60–70 % of biomass in turnip root takes place between 49–56 days after sowing. To understand the phenomenon of rapid sink filling, the activities of sucrose metabolising enzymes and carbohydrate composition in leaf blades, petiole and root of turnip from 42–66 days of growth were determined. An increase (2–3 folds) in glucose and fructose contents of roots accompanied by an increase in activities of acid and alkaline invertases was observed during rapid biomass accumulating phase of roots. The observed decrease in the activities of acid and alkaline invertases along with sucrose synthase (cleavage) in petiole during this period could facilitate unrestricted transport of sucrose from leaves to the roots. During active root filling period, a decrease in sucrose synthase (cleavage) and alkaline invertase activities was also observed in leaf blades. A rapid decline in the starch content of leaf blades was observed during the phase of rapid sink filling. These metabolic changes in the turnip plant led to increase in hexose content (35–37 %) of total dry biomass of roots at maturity. High hexose content of the roots appears to be due to high acid invertase activity of the root.     

Effect of water deficit on carbohydrate status and enzymes of carbohydrate metabolism in seedlings of wheat cultivars

The effect of water deficit on carbohydrate status and enzymes of carbohydrate metabolism (alpha and beta amylases, sucrose phosphate synthase, sucrose synthase, acid and alkaline invertases) in wheat (Triticum aestivum L.) was investigated in the seedlings of drought-sensitive (PBW 343) and drought-tolerant (C 306) cultivars. The water deficit was induced by adding 6% mannitol (water potential -0.815 Mpa) in the growth medium. The water deficit reduced starch content in the shoots of tolerant seedlings as compared to the sensitive ones, but increased sucrose content in the shoots and roots of tolerant seedlings, indicating their protective role during stress conditions. It also decreased the alpha-amylase activity in the endosperm of seedlings of both the cultivars, but increased alpha and beta amylase activities in the shoots of tolerant ones. Sucrose phosphate synthase (SPS) activity showed a significant increase at 6 days of seedling growth (DSG) in the shoots of stressed seedlings of tolerant cultivar. However, SPS activity in the roots of stressed seedlings of sensitive cultivar was very low at 4 DSG and appeared significantly only at day 6. Sucrose synthase (SS) activity was lower in the shoots and roots of stressed seedlings of tolerant cultivar than sensitive ones at early stage of seedling growth. Higher acid invertase activity in the shoots of seedlings of tolerant cultivar appeared to be a unique characteristic of this cultivar for stress tolerance. Alkaline invertase activity, although affected under water deficit conditions, but was too low as compared to acid invertase activity to cause any significant affect on sucrose hydrolysis. In conclusion, higher sucrose content with high SPS and low acid invertase and SS activities in the roots under water deficit conditions could be responsible for drought tolerance of C 306.     

Activity of sucrose hydrolysing enzymes and sugar accumulation during tomato fruit development

Relationships between the assimilate import rate and the activity of acid invertase and/or sucrose synthase have been investigated in the pericarp, locule and placenta of tomato fruit during development to establish the possible role of sucrose cleavage as the control step for the import of sucrose into these sink tissues. The rate of sucrose cleavage was estimated from the activities of these two enzymes as well as the ratio of hexoses to sucrose (i.e. the sucrose degradation index, SDI) in the tissues of the fruit, based on the assumption that the accumulation of hexoses is the consequence of imported sucrose being degraded by either or both of these two enzymes. The results showed that the change of sucrose synthase activity during fruit development was positively related to both the rate of dry matter accumulation in the fruit tissue and SDI. Although the role of acid invertase in regulating the rate of import during development remains uncertain, the actions of sucrose synthase on sucrose cleavage may regulate the import and compartmentation of sucrose in the early stage of tomato fruit development.     

A role for 'futile cycles' involving invertase and sucrose synthase in sucrose metabolism of tomato fruit.

Current concepts of the factors determining sink strength and the subsequent regulation of carbohydrate metabolism in tomato fruit are based upon an understanding of the relative roles of sucrose synthase, sucrose phosphate synthase and invertase, derived from studies in mutants and transformed plants. These enzymes participate in at least four futile cycles that involve sugar transport between the cytosol, vacuole and apoplast. Key reactions are (1) the continuous rapid degradation of sucrose in the cytosol by sucrose synthase (SuSy), (2) sucrose re-synthesis via either SuSy or sucrose phosphate synthase (SPS), (3) sucrose hydrolysis in the vacuole or apoplast by acid invertase, (4) subsequent transport of hexoses to the cytosol where they are once more converted into sucrose, and (5) rapid synthesis and breakdown of starch in the amyloplast. In this way futile cycles of sucrose/hexose interchange govern fruit sugar content and composition. The major function of the high and constant invertase activity in red tomato fruit is, therefore, to maintain high cellular hexose concentrations, the hydrolysis of sucrose in the vacuole and in the intercellular space allowing more efficient storage of sugar in these compartments. Vacuolar sugar storage may be important in sustaining fruit cell growth at times when less sucrose is available for the sink organs because of exhaustion of the carbohydrate pools in source leaves.     

Soluble acid invertase activity in leaves is independent of species differences in leaf carbohydrates, diurnal sugar profiles and paths of phloem loading

Leaf sucrose, starch, hexose and maximum extractable soluble acid invertase activity were compared throughout the day in source leaves of 13 plant species chosen for their putative phloem-loading type (apoplastic or symplastic). Four species which represent the different phloem-loading types (tomato, barley, maize and Fuchsia ) were studied in detail. Using this information we wished to determine whether a positive correlation between foliar carbohydrates and acid invertase activity exists in leaves from different species and, furthermore, whether this relationship is determined by phloem-loading type. Acid invertase activity was relatively constant throughout the day in all species. The extent of sucrose, hexose and starch accumulation and the sucrose: starch ratio measured at a given time were species-dependent. No correlations were found between foliar soluble acid invertase activity and the hexose, sucrose or starch content of the leaves in any of the species, regardless of phloem-loading type. The species examined could be divided into three distinct groups: (1) high sucrose, low invertase; (2) low sucrose, low invertase; and (3) low sucrose, high invertase. The absence of an inverse relationship between leaf sucrose, hexose or starch contents and endogenous soluble acid invertase suggests that this enzyme is not directly involved in carbon partitioning in leaves but serves an auxiliary function.     

Uptake of 13C-glucose by cell suspensions of carrot (Daucus carota) measured by in vivo NMR: Cycling of triose-, pentose- and hexose-phosphates

After a lag phase of 2 days, batch-grown cells of carrot ( Daucus carota L.) cv. Flakkese entered the exponential growth phase and started to accumulate sucrose and hexoses. Short-term feeding ¹³C-glucose in this period resulted in only minor labelling of sucrose or fructose. CO₂ production from [1-¹³C]- and [6-¹³C]-glucose revealed, that at least 40% of the added glucose passed through the oxidative pentose phosphate pathway (OPPP), up to 40% through glycolysis leaving only minor ¹³C-glucose for incorporation in various cell components in the exponential growth phase. After about 11 days of culture, the medium sugars were exhausted, cells entered the stationary growth phase and consumed stored sugar. Both neutral and acid invertase (EC 3.2.1.26) and sucrose synthase (EC 2.4.1.13) increased 50% from day 0 to days 11–13; thereafter their levels decreased again. Labelling with ¹³C-glucose resulted in the accumulation of labelled sucrose and fructose during the stationary growth phase. Sucrose labelling was transient, i.e. after 6 h its level started to decrease again. Labelled fructose, however, evolved slower and increased even after 8 h. In sucrose and fructose up to 20% of the ¹³C-label was exchanged from C-1 to C-6 carbons, indicating intensive cycling of at least 40% of the carbon between hexoses and triose phosphates. In the stationary phase only 10% of the labelled glucose passed through the OPPP and about 30% passed through the respiratory pathway; the remaining 60% was incorporated in cell constituents and sugars. Comparing the various cycles revealed that the regulation of the OPPP operated relatively independently from the cytosolic cycling of hexose phosphates through sucrose and from the cycling between hexose phosphates and triose phosphates.     

Activities of Sucrose Synthase and Acid Invertase in Pea Seedling Organs

The organ topography of sucrose synthase and soluble acid invertase in pea seedlings at heterotrophic stage (3–14 days) was studied. Sucrose synthase was most active in the roots, with the highest activity on the 6–8th days. In the leaves, its activity decreased from day 3 to day 14. In the stems, sucrose synthase activity was at an invariantly low level. The patterns of sucrose synthase activity in etiolated and green plants were similar. As distinct from sucrose synthase, invertase activity was the highest in the stem, especially in etiolated plants. The peak of its activity was observed on the 6-8th days. In the leaves, invertase activity was lower but its pattern was the same. In the roots, acid invertase activity decreased from the 3rd day and did not depend on illumination. The conclusion is that differences in sucrose synthase and acid invertase activities in roots, leaves, and stem are determined by differences in the import of hydrolytic products of stored compound from the cotyledons as well as by different demands of these organs for these products for the processes of organ expansion and for the maintenance of organ metabolism.     

Effects of Salt-Alkaline Stress on Carbohydrate Metabolism in Rice Seedlings

The aim of this study was to investigate carbohydrate metabolism in rice seedlings subjected to salt-alkaline stress. Two relatively salt-alkaline tolerant (Changbai 9) and sensitive (Jinongda 138) rice cultivars, grown hydroponically, were subjected to salt-alkaline stress via 50 mM of salt-alkaline solution. The carbohydrate content and the activities of metabolism-related enzymes in the leaves and roots were investigated. The results showed that the contents of sucrose, fructose, and glucose in the leaves and roots increased under salt-alkaline stress. Starch content increased in the leaves but decreased in the roots under salt-alkaline stress. The activities of sucrose-phosphate synthase, sucrose synthase, amylase, and ADP-glucose pyrophosphorylase increased whereas the activities of neutral invertase and acid invertase decreased in the leaves under salt-alkaline stress. The activities of sucrose-phosphate synthase, sucrose synthase, amylase, neutral invertase, and acid invertase increased in the roots under salt-alkaline stress. In conclusion, salt-alkaline stress caused the accumulation of photosynthetic assimilates in the leaves and decreased assimilation export to the roots.     

Cadmium induces changes in sucrose partitioning, invertase activities, and membrane functionality in roots of Rangpur lime (Citrus limonia L. Osbeck)

Cadmium (Cd) uptake effects on sucrose content, invertase activities, and plasma membrane functionality were investigated in Rangpur lime roots ( CITRUS LIMONIA L. Osbeck). Cadmium accumulation was significant in roots but not in shoots and leaves. Cadmium produced significant reduction in roots DW and increment in WC. Leaves and shoots did not show significant differences on both parameters. Sucrose content was higher in control roots than in Cd-exposed ones. Apoplastic sucrose content was much higher in Cd-exposed roots than in control ones. Cd-exposed roots showed a significant decrease in both cell wall-bound and cytoplasmic (neutral) invertase activities; while the vacuolar isoform did not show any change. Alterations in lipid composition and membrane fluidity of Cd-exposed roots were also observed. In Cd-exposed roots phospholipid and glycolipid contents decreased about 50 %, while sterols content was reduced about 22 %. Proton extrusion was inhibited by Cd. Lipid peroxidation and proton extrusion inhibition were also detected by histochemical analysis. This work's findings demonstrate that Cd affects sucrose partitioning and invertase activities in apoplastic and symplastic regions in Rangpur lime roots as well as the plasma membrane functionality and H (+)-ATPase activity.     

Carbohydrate partitioning and metabolism during acclimatization of micropropagated Calathea

Regulation of carbohydrate metabolism and compartmentation were studied during the acclimatization of tissue cultured Calathea plantlets. At transplantation plants were characterised by a heterotrophic metabolism with roots and stems as the main storage organs for carbohydrates. As acclimatization proceeded, a switch to autotrophic growth was observed: leaves became source organs, which was among others reflected by significant increases of invertase, sucrose synthase and sucrose-P synthase activities. Mobilization of reserves in roots and stems was also observed during the same period. Sucrose and starch accumulation in leaves was positively correlated with increasing light intensity.     

猕猴桃果实采后成熟过程中糖代谢及其调节

20℃下采后猕猴桃果实中淀粉酶活性快速上升于果实软化启动阶段,随着果实进入快速软化阶段,淀粉迅速水解,葡萄糖和果糖快速积累,SPS活性增加,酸性转化酶活性下降,蔗糖积累;至果实软化后期,SPS活性降低,蔗糖含量下降.AsA和低温可抑制淀粉酶活性、己糖积累、SPS活性上升和酸性转化酶活性下降,延缓蔗糖积累,相反,乙烯则可促进淀粉酶活性,加速淀粉降解和己糖积累进而直接或间接增加SPS活性,促使蔗糖积累.采后猕猴桃果实的SPS活性变化中有己糖激活效应和蔗糖反馈抑制效应.AsA、低温和乙烯等对糖代谢的调节主要是通过对SPS活性的影响而实现的.     

Analysis of carbohydrate metabolism enzymes and cellular contents of sugars and proteins during spruce somatic embryogenesis suggests a regulatory role of exogenous sucrose in embryo development.

Carbohydrate metabolism was investigated during spruce somatic embryogenesis. During the period of maintenance corresponding to the active phase of embryogenic tissue growth, activities of soluble acid invertase and alkaline invertase increased together with cellular glucose and fructose levels. During the same time, sucrose phosphate synthase (SPS) activity increased while sucrose synthase (SuSy) activity stayed constant together with the cellular sucrose level. Therefore, during maintenance, invertases were thought to generate the hexoses necessary for embryogenic tissue growth while SuSy and SPS would allow cellular sucrose to be kept at a constant level. During maturation on sucrose-containing medium, SuSy and SPS activities stayed constant whereas invertase activities were high during the early stage of maturation before declining markedly from the second to the fifth week. This decrease of invertase activities resulted in a decreased hexose:sucrose ratio accompanied by starch and protein deposition. Additionally, carbohydrate metabolism was strongly modified when sucrose in the maturation medium was replaced by equimolar concentrations of glucose and fructose. Essentially, during the first 2 weeks, invertase activities were low in tissues growing on hexose-containing medium while cellular glucose and fructose levels increased. During the same period, SuSy activity increased while the SPS activity stayed constant together with the cellular sucrose level. This metabolism reorganization on hexose-containing medium affected cellular protein and starch levels resulting in a decrease of embryo number and quality. These results provide new knowledge on carbohydrate metabolism during spruce somatic embryogenesis and suggest a regulatory role of exogenous sucrose in embryo development.     

Salinity Induces Accumulation of Soluble Sugars and Alters the Activity of Sugar Metabolising Enzymes in Rice Plants

Changes in the starch and sucrose contents, and the sucrose phosphate synthase, acid invertase, and starch phosphorylase activities were studied in the seedlings of salt sensitive and salt tolerant rice cultivars growing under two NaCl concentrations (7 and 14 dS m^-1) for 20 d. Under salinity, the starch content in roots declined more in salt sensitive cvs. Ratna and Jaya than in salt tolerant cvs. CSR-1 and CSR-3 and was unchanged in shoots. The contents of reducing and non-reducing sugars, and the activity of sucrose phosphate synthase was increased more in the sensitive than in the tolerant cultivars. Acid invertase activity decreased in shoots of the salt tolerant cultivars, whereas increased in salt sensitive cultivars. Starch phosphorylase activity decreased in all cultivars. This revised version was published online in July 2006 with corrections to the Cover Date.     

网纹甜瓜发育果实糖分积累与蔗糖代谢参与酶的关系

随着网纹甜瓜果实的发育,果实中葡萄糖和果糖的含量增加,蔗糖的快速积累发生在果实发育的中后期,高蔗糖积累型果实中蔗糖积累速率明显快于低蔗糖积累型.蔗糖磷酸合成酶活性在果实发育的前期短暂下降, 而后稳步上升,在果实发育的中后期高蔗糖积累型果实中该酶的活性显著高于低蔗糖积累型果实;随着果实发育,蔗糖合成酶的分解活性降低而合成活性升高.酸性和中性转化酶在未成熟果实中活性较高,而在成熟果实中很低; 高蔗糖积累型果实中酸性转化酶活性显著低于同期低蔗糖积累型果实.合成蔗糖的酶活性小于分解蔗糖的酶活性时蔗糖几乎没有积累.根据这些结果推测,转化酶活性的下降、蔗糖磷酸合成酶活性的增加以及蔗糖合成酶分解活性的下降和合成活性的增加,是引起果实蔗糖积累的主要内在因子.     

肉苁蓉和寄主梭梭体内可溶性糖分积累与蔗糖代谢相关酶活性研究

通过测定不同发育时期肉苁蓉和寄主梭梭体内主要糖类物质含量和蔗糖代谢相关酶活性,以研究寄生植物与寄主植物的糖代谢及其关系。结果表明:未寄生肉苁蓉的梭梭以积累葡萄糖为主,而寄生肉苁蓉的梭梭在夏季休眠期以积累葡萄糖为主,进入秋季旺盛生长期时以积累蔗糖为主。肉苁蓉的糖分积累与梭梭不同,己糖含量约占可溶性总糖的62.45%,而蔗糖仅为可溶性总糖的4.98%,故肉苁蓉为己糖积累型。寄主梭梭同化枝内蔗糖磷酸合成酶活性较转化酶活性和蔗糖合成酶活性低,其中寄生肉苁蓉的梭梭的分解酶类活性高于未寄生肉苁蓉的梭梭。肉苁蓉体内转化酶活性较低,而蔗糖合成酶和蔗糖磷酸合成酶活性较高,且蔗糖合成酶活性高于蔗糖磷酸合成酶活性,表现为肉苁蓉中的分解酶类活性高于合成酶类活性,较高的分解酶类活性促进了蔗糖的分解,从而促进了糖分由寄主梭梭向肉苁蓉的不断转移。总体来看,肉苁蓉和寄主梭梭体内糖分的代谢主要以蔗糖合成酶为主,其它2种酶为辅协同参与调控。     

Indole acetic acid mimics the effect of salt stress in relation to enzymes of carbohydrate metabolism in chickpea seedlings

The effect of addition of indole acetic acid (3 M) andNaCl (75 mM) on growth and enzymes of carbohydrate metabolism inchickpea seedlings was compared. In comparison with control seedlings, theseedlings growing in the presence of indole acetic acid (IAA) had reducedamylase activity in cotyledons and enhanced sucrose synthase (SS) and sucrosephosphate synthase (SPS) activities in cotyledons and shoots at all days ofseedling growth. Compared with control seedlings, sucrose content was higher incotyledons, shoots and roots and reducing sugar content was lower in shoots ofIAA treated seedlings. A low invertase (acid and alkaline) activity in shoots ofIAA treated seedlings could lead to reduced sink strength and hence decreasedgrowth of seedlings. Effects of NaCl stress on growth and activities of amylase,SS and SPS in cotyledons and invertase, SS and SPS in shoots were similar tothose observed with addition of IAA.