Carbon allocation in developing spruce needles. Enzymes and intermediates of sucrose metabolism

In lyophilized needles of Norway spruce ( Picea abies [L.] Karsten) and starting from bud break, we determined enzyme activities (sucrose phosphate synthase [SPS; EC 2.4,1.14]. sucrose synthase [SS; EC 2.4,1.13]. acid invertase [AI; EC 3.2,1.26]) and intermediates (starch, sucrose, glucose, fructose; fructose 6-phosphate, fructose 2.6-bisphosphate [F26BP]) of carbohydrate metabolism together with needle weight, shoot length, chlorophyll and protein. For up to 110 days after bud break, samples were taken twice a week from about 25-year-old trees under field conditions. At least three periods can be distinguished during needle maturation. During the first period (up to 45 days after bud break) Al showed the highest extractable activity. This coincided with very high levels of F26BP (up to 11 pmol [mg dry weight]⁻¹) and a transient increase of starch in parallel to a decrease of sucrose. The interval between 45 and 70 days after bud break was characterized by high SS activity (ratio of fructose/glucose >1), much decreased levels of F26BP (down to below 1 pmol [mg dry weight]⁻¹), and a pronounced increase in the dry weight/fresh weight ratio. In parallel, starch declined and soluble carbohydrates increased. Finally, needle maturation was characterized by decreasing SS and continuously increasing SPS activities, so that the ratio of SPS/SS increased more than 6-fold. AI. however, did not decline with maturation. Changes in pool sizes of metabolites and enzyme activities (AI. SPS) are consistent with current concepts on sink/source transition. SS is obviously important with regard to the synthesis of structural polysaccharides.     

Activities of enzymes of starch metabolism in developing Norway spruce [Picea abies (L.) Karst.] needles

 Development of spruce needles starts with high levels of starch. These are derived from imported sucrose, and, with some fluctuation, largely vanish during sink/source transition (Hampp et al. 1994, Physiol Plant 90: 299 – 306). In order to get more information about starch metabolism during this period, we collected current year needles of approximately 25-year-old Norway spruce trees [Picea abies (L.) Karst.] for up to 100 days starting from bud break. Levels of extractable activities of α-amylase (EC 3.2.1.1), ADP-glucose pyrophosphorylase (AGP, EC 2.7.7.27), D-enzyme (4-α-D-glucotransferase; EC 2.4.1.25), and of starch phosphorylase (STP, EC 2.4.1.1.) exhibited specific development-related responses. Insoluble starch dissolving α-amylase was close to the limit of detection for up to 70 days after bud break. At this stage, which marked the start of sink/source transition, α-amylase showed a rise in activity which could be related to the activity of sucrose phosphate synthase, a key enzyme of sucrose formation (correlation coefficient r = + 0.93). Similarly, the activity of AGP, a key enzyme of starch synthesis, was low during the initial phase of needle development and started to increase from about 60 days onwards. STP and D-enzyme, both involved in starch cycling, differed from each other. While STP activity changed in parallel to that of AGP, it was only the D-enzyme which showed appreciable rates shortly after bud break. We thus assume that in spruce needles D-enzyme is mainly responsible for starch turnover during the early period of development, whereas needle maturation, i. e. the acquisition of the ability to export photoassimilates, is characterized by an increased turnover of transitory starch – both synthesis (AGP) and degradation (α-amylase, STP) – and this is closely connected to the emergence of activity of the key enzyme of sucrose synthesis, sucrose phosphate synthase. Received: 16 October 1995 / Accepted: 20 February 1996     

Decrease in leaf sucrose synthesis leads to increased leaf starch turnover and decreased RuBP regeneration-limited photosynthesis but not Rubisco-limited photosynthesis in Arabidopsis null mutants of SPSA1

We investigated the individual effect of null mutations of each of the four sucrose‐phosphate synthase (SPS) genes in Arabidopsis (SPSA1, SPSA2, SPSB and SPSC) on photosynthesis and carbon partitioning. Null mutants spsa1 and spsc led to decreases in maximum SPS activity in leaves by 80 and 13%, respectively, whereas null mutants spsa2 and spsb had no significant effect. Consistently, isoform‐specific antibodies detected only the SPSA1 and SPSC proteins in leaf extracts. Leaf photosynthesis at ambient [CO₂] was not different among the genotypes but was 20% lower in spsa1 mutants when measured under saturating [CO₂] levels. Carbon partitioning at ambient [CO₂] was altered only in the spsa1 null mutant. Cold treatment of plants (4 °C for 96 h) increased leaf soluble sugars and starch and increased the leaf content of SPSA1 and SPSC proteins twofold to threefold, and of the four null mutants, only spsa1 reduced leaf non‐structural carbohydrate accumulation in response to cold treatment. It is concluded that SPSA1 plays a major role in photosynthetic sucrose synthesis in Arabidopsis leaves, and decreases in leaf SPS activity lead to increased starch synthesis and starch turnover and decreased Ribulose 1,5‐bisphosphate regeneration‐limited photosynthesis but not ribulose 1·5‐bisphosphate carboxylase/oxygenase (Rubisco)‐limited photosynthesis, indicating a limitation of triose‐phosphate utilization (TPU).     

Occurrence of sucrose and sucrose metabolizing enzymes in achlorophyllous algae

The presence of sucrose and the enzymes related to sucrose metabolism, i.e. sucrose synthase (SS) (UDP-glucose: D-fructose-2-glucosyl transferase, EC 2.4.1.13), sucrose phosphate synthase (SPS) (UDP-glucose: D-fructose-6-phosphate-2-glucosyl transferase, EC 2.4.1.14) and invertase (β-D-fructofuranoside fructohydrolase, EC 3.2.1.26) was demonstrated in Prototheca zopfii, a colorless alga. The levels of enzyme activities were lower than those obtained in Chlorella vulgaris, which is generally considered the photosynthetic counterpart of P. zopfii. Whem enzyme activities were measured in bleached cells of C. vulgaris, the levels were of the same order than those found in P. zopfii. These results would indicate that the sucrose metabolizing enzymes are not related to the algae ability to carry on photosynthesis.     

Photosynthesis, reserve mobilization and enzymes of sucrose metabolism in soybean (Glycine max) cotyledons

Soybean (Glycine max L. [Merr] cv. Ransom II) seedlings were grown under a light/ dark regime or in continuous darkness. Cotyledons were harvested daily for measurements of reserve mobilization, net carbon exchange rate, chlorophyll content and activities of certain enzymes involved in sucrose metabolism. Seedlings lost dry weight for the first 3 to 4 days after planting, then maintained a constant dry weight in the etiolated seedlings, and gained dry weight (via net fixation of CO₂) in the light-grown seedlings. In general, the patterns of reserve mobilization were as expected based on the collective work of other investigators. Soluble sugars were mobilized first, followed by protein and lipid. Galactinol, previously uncharacterized in soybean cotyledons, was present at low concentrations and was rapidly depleted within 2 days after planting. Mobilization of reserves was most important during the first 8 days after planting, whereas net cotyledonary photosynthesis began at 6 days after planting and was the primary source of assimilates after 8 days. Maximum rates of cotyledon photosynthesis were higher [up to 18 mg CO₂ (g dry weight)^?1 h^?1] than previously reported and accounted for about 75% of the assimilates transported from the cotyledons to the growing seedling during the functional life of the cotyledon. Enzyme activities in light-grown cotyledons peaked 7 to 10 days after planting and then declined. Sucrose phosphate synthase (EC 2.4.1.14) and sucrose synthase (EC 2.4.1.13) activities were similar in etiolated and light-grown seedlings, whereas uridine-5′-di-phosphatase (EC 3.6.1.6) activity was substantially higher in light-grown seedlings. During the period of reserve mobilization, the maximum sucrose phosphate synthase activity in cotyledonary extracts was in excess of the calculated rate of sucrose formation. However, when the cotyledons had highest net photosynthetic rates (14 days after planting), sucrose phosphate synthase activity was similar to the rate of carbon assimilation. It appears that soybean cotyledons are adapted for high rates of sucrose formation (from reserve mobilization and/or photosynthesis) for export to the rapidly growing tissues of the seedling.     

Localisation of sucrose-phosphate synthase and starch in leaves of C4 plants

The activity and intercellular distribution of sucrose-phosphate synthase (SPS; EC 2.4.1.14) were determined in fully expanded leaves from a range of C₄ plants. In Zea mays L. and Atriplex spongiosa F. Muell., SPS was located almost exclusively in the mesophyll cells. In other species, SPS was found in both cell types, with the activity in the bundle sheath cells ranging from 5% of the total leaf activity in Echinochloa crus-galli (L.) Beauv. to 35% in Sorghum bicolor Moench. At the end of the light period, starch was found only in the bundle sheath cells in all of the species examined. There appears to be little correlation between C₄-acid decarboxylation type and the location of sucrose and starch synthesis in the leaves of C₄ plants. Received: 18 October 1996 / Accepted: 20 November 1996     

Cold storage to overcome dormancy affects the carbohydrate status and photosynthetic capacity of Rhododendron simsii

Global warming leads to increasing irregular and unexpected warm spells during autumn, and therefore natural chilling requirements to break dormancy are at risk. Controlled cold treatment can provide an answer to this problem. Nevertheless, artificial cold treatment will have consequences for carbon reserves and photosynthesis. In this paper, the effect of dark cold storage at 7 °C to break flower bud dormancy in the evergreen Rhododendron simsii was quantified. Carbohydrate and starch content in leaves and flower buds of an early (‘Nordlicht’), semi‐early (‘M. Marie’) and late (‘Mw. G. Kint’) flowering cultivar showed that carbon loss due to respiration was lowest in ‘M. Marie’, while ‘Mw. G. Kint’ was completely depleted of starch reserves at the end of cold treatment. Gene isolation resulted in a candidate gene for sucrose synthase (SUS) RsSus, which appears to be homologous to AtSus3 and had a clear increase in expression in leaves during cold treatment. Photosynthesis measurements on ‘Nordlicht’ and the late‐flowering cultivar ‘Thesla’ showed that during cold treatment, dark respiration decreased 58% and 63%, respectively. Immediately after cold treatment, dark respiration increased and stabilised after 3 days. The light compensation point followed the same trend as dark respiration. Quantum efficiency showed no significant changes during the first days after cold treatment, but was significantly higher than in plants with dormant flower buds at the start of cold treatment. In conclusion, photosynthesis stabilised 3 days after cold treatment and was improved compared to the level before cold treatment.     

A comparison of the carbohydrate composition and kinetic properties of sucrose phosphate synthase (SPS) in transgenic tobacco (Nicotiana tabacum) leaves expressing maize SPS protein with untransformed controls

Tobacco plants, transformed with a maize sucrose phosphate synthase (SPS) cDNA clone, had threefold increased SPS activity compared to wild‐type tobacco. Measurement of SPS maximal activity and protein abundance using specific antibodies to the maize protein showed that the specific activity of the maize SPS protein was maintained when expressed in tobacco. Comparison of the kinetic properties of SPS in the transgenic lines compared to either wild‐type maize or tobacco revealed that the heterologously expressed protein had reduced affinity for both substrates (fructose‐6‐phosphate and UDP‐glucose) and reduced sensitivity to allosteric inhibition by inorganic phosphate. Moreover, the extent of light‐induced activation was reduced in the transgenic lines, with smaller changes observed in the K_m for both F6P compared to maize and tobacco wild‐type plants. Increased sucrose concentrations were observed in the transgenic lines at the end of the photoperiod and this was linearly related to SPS activity and associated with a parallel decrease in starch content. This suggests that SPS is a major control point for carbohydrate partitioning between starch and sucrose during photosynthesis.     

Leaflet photosynthesis rate and carbon metabolite accumulation patterns in nitrogen-limited, vegetative soybean plants

Prolonged inorganic nitrogen (NO₃ ^–+NH₄ ⁺) limitation of non-N₂-fixing soybean plants affected leaflet photosynthesis rates, photosynthate accumulation rates and levels, and anaplerotic carbon metabolite levels. Leaflets of nitrogen-limited (N-Lim), 27–31-day-old plants displayed 15 to 23% lower photosynthesis rates than leaflets of nitrogen-sufficient (N-Suff) plants. In contrast, N-Lim plant leaflets displayed higher sucrose and starch levels and rates of accumulation, as well as higher levels of carbon metabolites associated with sucrose and starch synthesis, e. g., glycerate-3-phosphate and glucose phosphates, than N-Suff plant leaflets. Concurrently, levels of soluble protein, chlorophyll, and anaplerotic metabolites, e.g., malate and phosphoenolpyruvate, were lower in leaflets of N-Lim plants than N-Suff plants, suggesting that the enzymes of the anaplerotic carbon metabolite pathway were lower in activity in N-Lim plant leaflets. Malate net accumulation rates in the earliest part of the illumination period were lower in N-Lim than in N-Suff plant leaflets; however, by the midday period, malate accumulation rate in N-Lim plant leaflets exceeded that in leaflets of N-Suff plants. Further, soluble protein accumulation rates in leaflets of N-Suff and N-Lim plants were similar, and the rate of dark respiration, measured in the early part of the dark period, was higher in N-Lim plant leaflets than in N-Suff plant leaflets. It was concluded that during prolonged N-limitation, foliar metabolite conditions favored the channelling of a large proportion of the carbon assimilate into sucrose and starch, while assimilate flow through the anaplerotic pathway was diminished. However, in some daytime periods, there was a normal level of carbon assimilate channelled through the anaplerotic pathway for ultimate use in amino acid and protein synthesis.Abbreviations ADPG-PPiase ADPglucose pyrophosphorylase - Ce CO₂ in the leaf photosynthesis measuring cuvette - Ci leaf internal CO₂ during photosynthesis measurement - Chl chlorophyll - DHAP dihydroxyacetone phosphate - GAP glyceraldehyde-3-phosphate - G_sw stomatal conductance with units as mmol H₂O m^–2 s^–1 - G1P glucose-1-phosphate - G6P glucose-6-phosphate - F6P fructose-6-phosphate - FBP fructose-1,6-bisphosphate - FBPase-pH 8.1 chloroplastic fructose-1,6-bisP (C-1) phosphatase (pH 8.1) - MAL malate - N inorganic nitrogen, i.e. NO₃ ^–+NH₄ ⁺ (at levels and molar ratios indicated) - PE post-emergence - PEP phosphoenolpyruvate - PEPCase phosphoenolpyruvate carboxylase - PGA 3-phosphoglycerate - PYR pyruvate - PYR kinase pyruvate kinase - Pn net CO₂ photoassimilation in leaves - PPFD photosynthetic photon flux density - PPRC pentose phosphate reductive cycle - RuBP ribulose-1,5-bisphosphate; rubisco-ribulose-1,5-bisphosphate carboxylase/oxygenase - SLW specific leaf mass - SPS sucrose-6-phosphate synthase - TCA cycle tricarboxylic acid cycle; triose-P-DAP+GAP     

Transgenic cotton over-producing spinach sucrose phosphate synthase showed enhanced leaf sucrose synthesis and improved fiber quality under controlled environmental conditions

Prior data indicated that enhanced availability of sucrose, a major product of photosynthesis in source leaves and the carbon source for secondary wall cellulose synthesis in fiber sinks, might improve fiber quality under abiotic stress conditions. To test this hypothesis, a family of transgenic cotton plants (Gossypium hirsutum cv. Coker 312 elite) was produced that over-expressed spinach sucrose-phosphate synthase (SPS) because of its role in regulation of sucrose synthesis in photosynthetic and heterotrophic tissues. A family of 12 independent transgenic lines was characterized in terms of foreign gene insertion, expression of spinach SPS, production of spinach SPS protein, and development of enhanced extractable V _max SPS activity in leaf and fiber. Lines with the highest V _max SPS activity were further characterized in terms of carbon partitioning and fiber quality compared to wild-type and transgenic null controls. Leaves of transgenic SPS over-expressing lines showed higher sucrose:starch ratio and partitioning of ¹⁴C to sucrose in preference to starch. In two growth chamber experiments with cool nights, ambient CO₂ concentration, and limited light below the canopy, the transgenic line with the highest SPS activity in leaf and fiber had higher fiber micronaire and maturity ratio associated with greater thickness of the cellulosic secondary wall.     

Decreased expression of two key enzymes in the sucrose biosynthesis pathway, cytosolic fructose-1,6-bisphosphatase and sucrose phosphate synthase, has remarkably different consequences for photosynthetic carbon metabolism in transgenic Arabidopsis thaliana

Photosynthetic carbon metabolism was investigated in antisense Arabidopsis lines with decreased expression of sucrose phosphate synthase (SPS) and cytosolic fructose-1,6-bisphosphatase (cFBPase). In the light, triose phosphates are exported from the chloroplast and converted to sucrose via cFBPase and SPS. At night, starch is degraded to glucose, exported and converted to sucrose via SPS. cFBPase therefore lies upstream and SPS downstream of the point at which the pathways for sucrose synthesis in the day and night converge. Decreased cFBPase expression led to inhibition of sucrose synthesis; accumulation of phosphorylated intermediates; Pi-limitation of photosynthesis; and stimulation of starch synthesis. The starch was degraded to maintain higher levels of sugars and a higher rate of sucrose export during the night. This resembles the response in other species when expression of enzymes in the upper part of the sucrose biosynthesis pathway is reduced. Decreased expression of SPS inhibited sucrose synthesis, but phosphorylated intermediates did not accumulate and carbon partitioning was not redirected towards starch. Sugar levels and sucrose export was decreased during the night as well as during the day. Although ribulose-1,5-bisphosphate regeneration and photosynthesis were inhibited, the PGA/triose-P ratio remained low and the ATP/ADP ratio high, showing that photosynthesis was not limited by the rate at which Pi was recycled during end-product synthesis. Two novel responses counteracted the decrease in SPS expression and explain why phosphorylated intermediates did not accumulate, and why allocation was not altered in the antisense SPS lines. Firstly, a threefold decrease of PPi and a shift of the UDP-glucose/hexose phosphate ratio favoured sucrose synthesis and prevented the accumulation of phosphorylated intermediates. Secondly, there was no increase of AGPase activity relative to cFBPase activity, which would prevent a shift in carbon allocation towards starch synthesis. These responses are presumably triggered when sucrose synthesis is decreased in the night, as well as by day.     

稻纵卷叶螟和白背飞虱序列危害及间隔天数对水稻生理生化的影响

【目的】为了解稻纵卷叶螟Cnaphalocrocis medinalis和白背飞虱Sogatella furcifera的复合危害对水稻产量相关因子和相关酶类的影响。【方法】本文设定两种害虫的先后危害顺序,并通过调整两者开始危害的时间,研究了受害后水稻在灌浆期根、茎和叶片中淀粉和蔗糖含量的变化以及蔗糖合成酶(Sucrose synthase,SS)和蔗糖磷酸合成酶(Sucrose phosphate synthase,SPS)活性的变化。【结果】随着接虫量的增加,水稻不同组织内各生理指标与对照相比均显著下降。随着间隔天数的增加,先接白背飞虱为害要重于先接稻纵卷叶螟。比如叶片中蔗糖含量在先接稻纵卷叶螟的处理中随着间隔天数的增加显著增加,相应的SPS活性显著增加,间隔24 d的处理显著高于间隔6 d和12 d;而先接白背飞虱的处理中蔗糖含量与SPS活性均显著降低,间隔24 d的处理显著低于间隔6 d和12 d的处理。茎部淀粉含量在先接稻纵卷叶螟的处理中随着间隔天数的增加逐渐增加,SS活性显著增加,而先接白背飞虱的处理中淀粉含量和SS活性均显著降低;叶片中淀粉含量均随着间隔天数的增加逐渐降低,而相应的SS活性在先接稻纵卷叶螟的处理中显著增加,在先接白背飞虱的处理中相反。另外,接虫量和间隔天数间有显著的交互作用。【结论】本研究对指导水稻生产中的"两迁害虫"防治具有潜在应用价值。     

Carbohydrate and carbon metabolite accumulation responses in leaves of ozone tolerant and ozone susceptible spinach plants after acute ozone exposure

The objective of this study was to determine whether exposure of plants to ozone (O₃) increased the foliar levels of glucose, glucose sources, e.g., sucrose and starch, and glucose-6-phosphate (G6P), because in leaf cells, glucose is the precursor of the antioxidant, L-ascorbate, and glucose-6-phosphate is a source of NADPH needed to support antioxidant capacity. A further objective was to establish whether the response of increased levels of glucose, sucrose, starch and G6P in leaves could be correlated with a greater degree of plant tolerance to O₃. Four commercially available Spinacia oleracea varieties were screened for tolerance or susceptibility to detrimental effects of O₃ employing one 6.5 hour acute exposure to 25O nL O₃ L^-1 air during the light. One day after the termination of ozonation (29 d post emergence), leaves of the plants were monitored both for damage and for gas exchange characteristics. Cultivar Winter Bloomsdale (cv Winter) leaves were least damaged on a quantitative grading scale. The leaves of cv Nordic, the most susceptible, were approximately 2.5 times more damaged. Photosynthesis (Pn) rates in the ozonated mature leaves of cv Winter were 48.9% less, and in cv Nordic, 66.2% less than in comparable leaves of their non-ozonated controls. Stomatal conductance of leaves of ozonated plants was found not to be a factor in the lower Pn rates in the ozonated plants. At some time points in the light, leaves of ozonated cv Winter plants had significantly higher levels of glucose, sucrose, starch, G6P, G1P, pyruvate and malate than did leaves of ozonated cv Nordic plants. It was concluded that leaves of cv Winter displayed a higher tolerance to ozone mediated stress than those of cv Nordic, in part because they had higher levels of glucose and G6P that could be mobilized during diminished photosynthesis to generate antioxidants (e.g., ascorbate) and reductants (e.g., NADPH). Elevated levels of both pyruvate and malate in the leaves of ozonated cv Winter suggested an increased availability of respiratory substrates to support higher respiratory capacity needed for repair, growth, and maintenance.Abbreviations ADPG-PPiase ADPglucose pyrophosphorylase - ASC L-ascorbic acid - APX ascorbate peroxidase - Ce CO₂ concentration in air in the measuring cuvette during photosynthesis measurements - Ci CO₂ concentration in the leaf intercellular spaces during photosynthesis measurement - Chl chlorophyll - DHA dehydroascorbic acid - DHA reductase dehydroascorbate reductase - DHAP dihydroxyacetone phosphate - GAP glyceraldehyde-3-phosphate - Gluc glucose - GR glutathione reductase - G_sw stomatal conductance with units as mmol H₂O m^-2 s^-1 - GSSG oxidized glutathione - GSH reduced glutathione - G1P glucose-1-phosphate - G6P glucose-6-phosphate - G6P dehydrogenase glucose-6-phosphate dehydrogenase - 6PG 6-phosphogluconate - 6PG dehydrogenase 6-phosphogluconate dehydrogenase - F6P fructose-6-phosphate - FBP fructose-1,6-bisphosphate - MAL malate - MDHA reductase monodehydroascorbate reductase - PE post-emergence - PEP phosphoenolpyruvate - PGA 3-phosphoglycerate - Pi orthophosphate - PYR pyruvate - Pn net CO₂ photoas-similation in leaves - PPFD photosynthetic photon flux density with units of mol photons m^-2 s^-1 - PPRC pentose phosphate reductive cycle - RuBP ribulose-1,5-bisphosphate - rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase - SLW specific leaf weight - TCA cycle tricarboxylic acid cycle - Triose-P DHAP+GAP     

Opposite effects of exogenous sucrose on growth, photosynthesis and carbon metabolism of in vitro plantlets of tomato (L. esculentum Mill.) grown under two levels of irradiances and CO2 concentration

The long-term effects of exogenous sucrose (3 percnt;) on growth, photosynthesis and carbon metabolism ofin vitro tomato plantlets were investigated under two sets of growth conditions that respectively favor source- or sink-limitations of photosynthesis: 1) low photosynthetic photon flux (PPF) (50 μmol m⁻² · s⁻¹) and low CO₂ concentration (400 μmol mol⁻¹) and 2) high PPF (500 μmol m⁻² · s⁻¹ and high CO₂ concentration (4000 μmol mol⁻¹). The supply of sucrose under source-limitation conditions increased the growth, the maximal photosynthetic rate, the chl content, the maximal quantum yield of Photosystem II estimated by the Fv/Fm chl fluorescence ratio as well as the soluble sugars (hexoses, sucrose) and starch contents in roots, young and mature leaves when compared to those of photo-autotrophic plantlets. Also, sucrose feeding under these conditions strongly increased the activity of sucrose synthase (SS) (EC 2.4.1.13) in roots and young leaves whereas the activities of sucrose phosphate synthase (SPS) (EC 2.4.1.14), acid invertase (INV) (EC 3.2.1.26) and ADP-glucose pyrophosphorylase (ADPGppase) (EC 2.7.7.27) were highly stimulated in roots and mature leaves. Contrary to these observations, the supply of sucrose to plantlets developed under high PPF and CO₂ concentration decreased growth and led to a somewhat lower maximal photosynthetic rate relative to photo-autotrophic plantlets. These negative responses to exogenous sucrose were accompanied by stronger accumulations of hexose and starch, larger stimulation of INV in mature leaves developed under conditions of sink limitation than those from source limitation conditions. Moreover, under high PPF and high CO₂ concentration, exogenous sucrose led to a marked repression of the SPS activity and caused much lower stimulations of ADPGppase in mature leaves than those observed at low PPF and low CO₂ concentration. We therefore conclude that under our experimental conditions, the interactive effects of exogenous sucrose and environmental conditions on growth and photosynthesis could be rationalized by the source-sink equilibrium of thein vitro tomato plantlets.     

Up-regulation of sucrose metabolizing enzymes in Oncidium goldiana grown under elevated carbon dioxide

Experiments were conducted in controlled growth chambers to evaluate how increase in CO₂ concentration affected sucrose metabolizing enzymes, especially sucrose phosphate synthase (SPS; EC 2.4.1.14) and sucrose synthase (SS; EC 2.4.1.13), as well as carbon metabolism and partitioning in a tropical epiphytic orchid species (Oncidium goldiana). Response of ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco; EC 4.1.1.39) to elevated CO₂ was determined along with dry mass production, photosynthesis rate, chlorophyll content, total nitrogen and total soluble protein content. After 60 days of growth, there was a 80% and 150% increase in dry mass production in plants grown at 750 and 1 100 μl l^?1 CO₂, respectively, compared with those grown at ambient CO₂ (about 370 μl l^?1). A similar increase in photosynthesis rate was detected throughout the growth period when measured under growth CO₂ conditions. Concomitantly, there was a decline in leaf Rubisco activity in plants in elevated CO₂ after 10 days of growth. Over the growth period, leaf SPS and SS activities were up‐regulated by an average of 20% and 40% for plants grown at 750 and 1100 μl l^?1 CO₂, respectively. Leaf sucrose content and starch content were significantly higher throughout the growth period in plants grown at elevated CO₂ than those at ambient CO₂. The partitioning of photosynthetically fixed carbon between sucrose and starch appeared to be unaffected by the 750 μl l^?1 CO₂ treatment, but it was favored into starch under the 1 100 μl l^?1 CO₂ condition. The activities of SPS and SS in leaf extracts were closely associated with photosynthetic rates and with partitioning of carbon between starch and sucrose in leaves. The data are consistent with the hypothesis that the up‐regulation of leaf SPS and SS might be an acclimation response to optimize the utilization and export of organic carbon with the increased rate of inorganic‐carbon fixation in elevated CO₂ conditions.     

Altered photosynthesis,flowering, and fruiting in transgenic tomato plants that have an increased capacity for sucrose synthesis

Photosynthesis, leaf assimilate partitioning, flowering, and fruiting were examined in two lines of Lycopersicon esculentum Mill. transformed with a gene coding for sucrose-phosphate synthase (SPS) (EC 2.3.1.14) from Zea mays L. expressed from a tobacco ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) small subunit promoter. Plants were grown at either 35 or 65 Pa CO₂ and high light (1000 mol photons·m^–2·s^–1). Limiting and maximum SPS activities were significantly greater (up to 12 times) in the leaves of SPS-transformed lines for all treatments. Partitioning of carbon into sucrose increased 50% for the SPS transformants. Intact leaves of the control lines exhibited CO₂-insensitivity of photosynthesis at high CO₂ levels, whereas the SPS transformants did not exhibit CO₂-insensitivity. The O₂-sensitivity of photosynthesis was also greater for the SPS-transformed lines compared to the untransformed control when measured at 65 Pa CO₂. These data indicate that the SPS transformants had a reduced limitation on photosynthesis imposed by end-product synthesis. Growth at 65 Pa CO₂ resulted in reduced photosynthetic capacity for control lines but not for SPS-transformed lines. When grown at 65 Pa CO₂, SPS transformed lines had a 20% greater photosynthetic rate than controls when measured at 65 Pa CO₂ and a 35% greater rate when measured at 105 Pa CO₂. Photosynthetic rates were not different between lines when grown at 35 Pa CO₂. The time to 50% blossoming was reduced and the total number of inflorescences was significantly greater for the SPS transformants when grown at either 35 or 65 Pa CO₂. At 35 Pa CO₂, the total fruit number of the SPS transformants was up to 1.5 times that of the controls, the fruit matured earlier, and there was up to a 32% increase in total fruit dry weight. Fruit yield was not significantly different between the lines when grown at 65 Pa CO₂. Therefore, there was not a strict relationship between yield and leaf photosynthesis rate. Flowering and fruit development of the SPS-transformed lines grown at 35 Pa CO₂ showed similar trends to the controls grown at 65 Pa CO₂. Incidences of blossom-end rot were also reduced in the SPS-transformed lines. These data indicate that altering starch/sucrose partitioning by increasing the capacity for sucrose synthesis can affect acclimation to elevated CO₂ partial pressure and flowering and fruiting in tomato.Abbreviations DAS days after seeding - nptII neomycin phos-photransferase - Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase - RuBP ribulose-1,5-bisphosphate - SPS sucrose-phosphate synthase - SSU Rubisco small subunit This research was supported by U.S. Department of Energy grant FG02-87ER13785. B.J.M. thanks the Natural Sciences and Engineering Research Council of Canada for financial support. We are grateful to Toni A. Voelker (Calgene Inc.) for supplying tomato seeds and valuable advice.     

Relations between carbohydrate accumulation in leaves, sucrose phosphate synthase activity and photoassimilate transport in chilling treated maize seedlings

Sucrose and starch concentration, sucrose phosphate synthase (SPS) activity in leaves, and long distance transport were studied in maize seedlings treated with moderate chilling (14 °C/12 °C - day/night). Two inbred lines were tested: chilling-tolerant KW1074 and chilling-sensitive CM109. Seedlings were grown in phytotrone on water nutrient until the 4-th leaf appearance. The estimations were done on fully developed 2-nd leaf. Six days after the temperature was lowered, leaves of line KW 1074 plants contained 5-fold more sucrose and starch than the control ones. The same treatment of CM 109 seedlings resulted in accumulation of sucrose and starch by 2-fold and 8.5-fold, respectively. As the result of chilling-treatment, ¹⁴C assimilation rate (P_a), transport speed in the leaf blade (TS₁) and along the plant (TS_m) decreased by about 50 % in both lines. On the other hand, time necessary for radiolabel movement into the phloem loading region (AT) increased strongly, especially in chilling-sensitive line CM 109. It was also noted, that the radioactivity exported from leaves (R₁) and imported by roots (R_m) decreased in line CM 109, and increased slightly in line KW 1074. The activity of SPS extracted from leaves of both lines decreased by about 3.3 when temperature was lowered form 30°C to 10°C. There was no effect of 6 day treatment of chilling on SPS activity. Changes in sucrose and starch concentration, SPS activity as well as differences in transport parameters observed in KW1074 and CM109 seedlings at moderate low temperatures are discussed in terms of mechanism of maize chilling-sensitivity.     

Sucrose-Phosphate Synthase,Sucrose Synthase,and Invertase in Sugar Beet Leaves

The activity of sucrose-phosphate synthase (SPS) in sugar beet (Beta vulgaris L.) leaves was shown to exceed considerably the synthesizing activity of sucrose synthase (SS). The rise in SPS activity was related to the daylight period; i.e., it was associated with the rate of photosynthesis. The highest SPS activity was characteristic of fully expanded source leaves. In young developing leaves (leaves expanded to less than half of their final size), which represent the sink organs, the SPS activity was 2.5 times lower. At all stages of leaf development, the synthesizing SS activity was rather low. The diurnal change of SS activity was independent of photosynthesis and showed a slight rise from 6:00–8:00 p.m. Under field conditions, the highest SPS activity was found in leaves in the terminal stage of their development (105-day-old plants); the synthesizing activity of SS showed little changes during this period. The activity of soluble acid invertase was characteristic of young leaves. In mature leaves, the activity of this enzyme correlated with the daylight period. These changes occurred on the background of low sucrose content in leaves. The regulation of SPS, SS, and invertase activity is discussed. It is supposed that compartmentation of these enzymes in the photosynthesizing cell is important for transport, metabolism, and the osmotic function of sucrose in leaves.     

Coarse control of sucrose-phosphate synthase in leaves: Alterations of the kinetic properties in response to the rate of photosynthesis and the accumulation of sucrose

It has been investigated whether diurnal rhythms of sucrose-phosphate synthase (SPS) are involved in controlling the rate of photosynthetic sucrose synthesis. Extracts were prepared from spinach (Spinacia oleracea L.) and barley (Hordeum vulgare L.) leaves and assayed for enzyme activity. The activity of SPS increased in parallel with a rising rate of photosynthesis, and was increased by feeding mannose and decreased by supplying inorganic phosphate. In leaf material where sucrose had accumulated during the photoperiod or when sucrose was supplied exogenously, SPS activity decreased. During a diurnal rhythm, SPS activity increased after illumination, declined gradually during the light period, decreased further after darkening and then recovered gradually during the night. These changes did not involve an alteration of the maximal activity, but were caused by changes in the kinetic properties, revealed as a change in sensitivity to inhibition by inorganic phosphate. In experiments which modelled the response of SPS to changing metabolite concentrations, it was shown that these alterations of kinetic properties would strongly modify the activity of SPS in vivo. It is proposed that SPS can exist in kinetically distinct forms in vivo, and that the distribution between these forms can be rapidly altered. As the rate of photosynthesis increases there is an activation of SPS, which may be directly or indirectly linked to changes in the availability of P_i. This activation can be modified by factors related to the accumulation of sucrose. Under normal conditions there is a balance between these factors, and the leaf contains a mixture of the different forms of SPS.Abbreviations Chl chlorophyll - Frul,6bisP fructose-1,6-bisphosphate - Fru2,6bisP fructose-2,6-bisphosphate - Fru6P fructose-6-phosphate - Fru1,6bisPase fructose-1,6-bisphosphatase - Fru6P 2kinase fructose-6-phosphate, 2kinase - Fru2,6bisPase fructose-2,6-bisphosphatase - Glc6P glucose-6-phosphate - P_j inorganic phosphate - SPS sucrose-phosphate synthase - UDPGLc uridine 5-diphosphate glucose     

Carbon partitioning in Norway spruce: amounts of fructose 2,6-bisphosphate and of intermediates of starch/sucrose synthesis in relation to needle age and degree of needle loss

Summary Intermediates involved in carbon partitioning between starch and sucrose [dihydroxyacetone phosphate + glyceraldehyde 3-phosphate (TP), 3-phosphoglyceric acid, fructose 6-phosphate (F6P), fructose 2,6-bisphosphate (F26BP), in addition to glucose, fructose, sucrose and starch] were analysed in lyophilized needles of Norway spruce (Picea abies L. Karst). Samples were taken from all distinct parts of first and second order branches and the analysed data related to season, needle age, needle position and degree of needle loss (control and class 2 approx. 30%–40% needle loss). Positive and inverse correlations of F26BP, an important regulator of carbon partitioning between starch and sucrose, and F6P or TP existed in all samples. F26BP levels were highest in developing needles and gradually decreased during maturation, which is possibly indicative of changes in the relative sink strength during development (switch from import to export of sucrose). In class 2 needles the amount of F26BP was significantly increased. Together with nearly unaltered levels of sucrose but only slightly decreased amounts of starch the results can be taken as evidence for impaired carbon export in our class 2 samples. The data are discussed with respect to needle development and a possible impact of both air pollutants and mineral deficiency at the location from which the samples were taken.