SPS Activity Research Articles

Changes of Matter Accumulation and Relative Enzymatic Activity during Yam Tuber Development

Tuber development is a complex physiological process,involving in changes of various components and enzymes activities,so learning about changes of the matter accumulation and enzymes metabolism will help to instruct yam production.In the paper,two different cultivars Guihuai 5 and Guihuai 16 were used to investigate some physiological and biochemical indicators during yam tuber development in 2009—2010.The results showed that tuber length and dry matter content were kept increasing,but AMY enzyme activity decreasing during the tuber development.The main carbohydrates contents,functional substances,and the activities of POD,AI,and SPS presented similar trend:continually increased firstly,and reached various peaks,then decreased.The changes of reducing sugar content and AGPase activity were different between two cultivars.The t-test results indicated that there was a significant difference between two cultivars in dry matter (P=0.011),starch (P=0.031),and saponin (P=0.019).Sucrose content was significantly correlated with soluble sugars content (r5 =0.97**,r16 =1.00**),AGPase activity (r5=-0.85*) and reducing sugars content (r16 =0.87*),and starch content was significantly correlated with polysaccharides (r5 =0.95**),Vc(r5 =0.83*) and saponin (r16 =0.88**) contents as well as tuber length was significantly correlated with dry matter content (r5 =0.97**,r16 =0.87*),AMY activity (r16=-0.95**),AGPase activity (r16=-0.90**),and protein content (r16 =0.83*).To sum up,the sucrose accumulation,SPS and AI activity play a key regulatory effect in yam tuber development,the main functional substances are close correlated between each other.

Chilling privation during dormancy period and carbohydrate mobilization in Japanese pear trees

The flower bud abortion is one of the main problems that limit commercial pear (Pyrus pyrifolia) production in the southern region of Brazil. Insufficient chilling during the dormancy period is known as the main factor of this problem. One of the hypotheses to explain this problem is that the starch mobilization and carbohydrate fluxes to the buds are impeded when mild temperatures occurred during winter. This study compared the total soluble sugars (TSS) and reducing sugars (RS) concentrations, the cell wall acid invertase (CWAI - EC 3.2.1.26) and sucrose-phosphate synthase (SPS - EC 2.4.1.14) activities in wood of branches and floral buds of Japanese pear trees cv. Housui, grafted on Pyrus calleryana and submitted to chilling conditions during the dormancy period. Treatments were: (i) natural conditions; (ii) continuous artificial chilling; (iii) alternating temperatures, and (iv) total chilling privation. TSS and RS contents, as well as CWAI and SPS activities in tissues of branches that received insufficient chilling were lower than those that received sufficient chilling during winter. The starch concentration was superior in wood tissues of branches kept under chilling privation. The chilling privation disturbs carbohydrate mobilization in pear trees, reducing the sucrose synthesis capacity in wood tissues (source) and sucrose importation by the floral buds (sink).

Investigation of Copper Plating and Additive Interactions in the Presence of Fe3+/Fe2+ Redox Couple

The impact of the ferric/ferrous (Fe3+/Fe2+) redox couple on the behavior of polyethylene glycol (PEG) and bis-(3-sulfopropyl) disulfide (SPS) during copper electrodeposition is investigated. The Fe3+/Fe2+ couple is used in plating of copper onto printed circuit boards and may have advantages when implemented for on-chip metallization of copper. Experiments show that in the presence of Fe3+/Fe2+ the suppressing behavior of PEG does not change; in contrast, the accelerating activity of SPS increases when Fe3+/Fe2+ is present in a copper-plating bath. Furthermore, potentiostatic experiments suggest that SPS interacts with Fe2+ ions in the bulk electrolyte, probably to produce 3-mercapto-1-propane sulfonic acid (MPS) at low ppb levels.

Acid invertase as a serious candidate to control the balance sucrose versus (glucose + fructose) of banana fruit during ripening

Six banana varieties: 3 ‘dessert’ ones: ‘IDN 110’; ‘Kirun’; and ‘Grande Naine’, and 3 ‘cooking’ ones: ‘Galéo’; ‘Sowmuk’; and ‘French’ were used to investigate the relationship between sugar profiles and activities of sucrose-phosphate synthase (SPS, EC 2.4.1.14), sucrose synthase (SuSy, EC 2.4.1.13) working in the hydrolytic way, invertases (EC 3.2.1.26) (neutral (NIV) and acid (AIV)). Expression of a Musa cell-wall invertase ( MaCwINV1/ pBANUU103) gene was additionally studied during fruit development and ripening ex planta after ethylene treatment of two of these varieties. Close amounts of soluble sugars (sucrose + glucose + fructose) were measured in the different varieties at ripe stage. SPS activity was either almost constant or increased continuously or transitorily during ripening of all varieties, concomitantly to total soluble sugar (sucrose + glucose + fructose) accumulation. Together with previous data obtained from ‘Cavendish’, our data lead us, (i) to strengthen the hypothesis that this enzyme is likely to have a major role in the synthesis of sucrose during ripening of banana and (ii) to underline the complexity of the mode of SPS activity regulation already pointed out. Interestingly, for the first time in banana, two diploid and cooking varieties: ‘Galéo’ and ‘Sowmuk’ were found almost sucrose-free, in good agreement with a 6.4-fold higher mostly vacuolar AIV activity than that of the two desserts and diploid ones. Otherwise, expression of a MaCwINV1/ pBANUU103 (cell wall) gene was followed in the two most contrasted varieties in matter of sucrose content: ‘Sowmuk’ almost sucrose-free, and ‘IDN 110’ accumulating high level of sucrose. Compared to ‘IDN110’, the mRNA level of MaCwINV1/ pBANUU103 gene was higher (up to 173-fold) in ‘Sowmuk’ concomitantly with the low level of sucrose of ‘Sowmuk’. Our data let us to conclude that the AIV is probably one of the main determinants involved in the regulation of sucrose level during banana fruit ripening, even if the form, vacuolar or cell wall-linked is not determined yet. Otherwise, the MaCwINV1/ pBANUU103 gene appears as a putative candidate gene that could contribute to regulate this level.

Osmotic Potential, Sucrose Level, and Activity of Sucrose Metabolic Enzymes in Tall Fescue in Response to Deficit Irrigation

Effects of deficit irrigation applied to home lawns, used as means of water conservation, are an important issue. However, the impact of deficit irrigation on sucrose metabolism in tall fescue (Festuca arundinacea) is unknown and important because sucrose is the dominant form of carbohydrate transported to developing plant organs. The objectives of this study were to investigate the effects of deficit irrigation on leaf water content, osmotic potential (ψS), sucrose level, and the activity of sucrose phosphate synthase (SPS; EC 2.4.1.14), sucrose synthase (SS; EC 2.4.1.13), and acid invertase (AI; EC 3.2.1.26) in tall fescue leaves. Sods of ‘Falcon II’ tall fescue were established in polyvinylchloride (PVC) tubes (10 cm diameter × 40 cm long) filled with a mixture of sand and fritted clay [9:1 (v:v)] and then placed in growth chambers. Reference evapotranspiration rate [ETo (millimeters of water per day)] was determined by weighing the PVC tubes containing well-watered turfgrass every 3 days to determine water loss on a daily basis as ETo. Deficit irrigation treatments were applied as follows: well-watered control, mild drought stress (60% ETo), and severe drought stress (20% ETo). Leaf water content was lower at 6, 12, and 20 days of treatment for the 20% ETo treatment and 20 days after treatment began for the 60% ETo treatment. Compared with the well-watered control, ψS was lower in the 60% ETo treatment on all three measurement dates. Sucrose was higher at 8 and 14 days after treatment began in the 60% ETo treatment and on all three measurement dates in the 20% ETo treatment relative to the well-watered control. No difference in sucrose level was observed between the 20% ETo and 60% ETo irrigation regimes at 8 and 14 days of treatment. Beginning 14 days after treatment, tall fescue had a higher level of SPS in the 60% ETo and 20% ETo treatments compared with the well-watered treatment. Tall fescue receiving 60% or 20% ETo had a lower level of AI activity on all measurement dates. Results suggest that the decrease in ψS was accompanied by higher sucrose levels, which were the result of the increased level of SPS and SS activity and a decline in AI activity.

Alterations in biomarkers of endothelial function following on‐pump coronary artery revascularization

Cardiopulmonary bypass (CPB) has been associated with activation and injury of endothelial cells, probably responsible for the systemic inflammatory response syndrome (SIRS) taking place in these patients. We measured plasma concentrations of soluble P-selectin (sP-s), E-selectin (sE-s), tetranectin (TN), vonWillebrand factor (vWF) levels, and angiotensin-converting enzyme (ACE) activity in 31 adult patients undergoing elective coronary artery bypass grafting, just before and up to three days after surgery, and in 25 healthy volunteers. Patients showed higher plasma sP-s and sE-s and ACE concentrations, just before surgery, but significantly lower TN levels, compared with controls. During the first three postoperative days (PD), the concentration of each of the molecules followed a different and independent pattern, although in the third PD, the levels of sP-s, sE-s and ACE were higher and those of vWF and TN lower, compared with the preoperative ones. However, patients had higher sP-s (P=0.06), sE-s (P=0.07), and vWF (P=0.005), but lower TN concentrations (P=0.02) on the third PD compared with controls. CPB is characterised by pronounced changes in plasma sP-s, sE-s, TN, vWF levels, and ACE activity, which are associated with significant alteration in the intra- and early postoperative endothelial function observed in open heart surgery.

Changes in sugar content and relative enzyme activity in grape berry in response to root restriction

Root restriction often depresses photosynthetic capacity and reduces shoot growth, but the photosynthate accumulation in fruit under restriction is higher than in control fruit. However, changes in metabolism responsible for these differences are unclear. To identify the metabolic mechanism by which root restriction affects sugar accumulation in fruit of ‘Kyoho’ grape ( Vitis vinifera × V. labruscana), sugar metabolism and related enzyme activities in grape berries produced with and without root restriction were compared. Total sugar content of fruit produced under root restriction was higher than that of control fruit. Acid invertase (AI, EC 3.2.1.26) activity, which increases with berry development, was significantly higher in root-restricted berries than in control berries. Neutral invertase (NI, EC 3.2.1.26) activity showed a similar trend to AI, but the amount of NI activity was lower than AI in both treatments. Sucrose phosphate synthase (SPS, EC 2.4.1.14) and sucrose synthase (SS, EC 2.4.1.13) activity changed slightly with berry development, and there was no significant difference in SS and SPS activity between root restriction and control treatments. Therefore, AI appears to be the key enzyme induced by root restriction that explains the higher sugar content found in grape berry produced under root restriction.

Atividade de enzimas relacionadas com a mobilização de carboidratos durante a dormência da nogueira (Juglans Regia)

A brotação da nogueira é dependente da mobilização de carboidratos do lenho para as gemas localizadas na porção superior dos ramos. O objetivo do trabalho foi contribuir para o entendimento do mecanismo de brotação acrótona da nogueira, em clima temperado, através da mensuração da atividade da ±-amilase (EC 3.2.1.1) e sacarose fosfato sintase (SPS - EC 2.4.1.14) relacionadas com a mobilização de carboidratos, durante o período de dormência. Para cada coleta, foram amostrados cinco ramos do ano, durante os meses de setembro a março. Em abril, próximo à retomada do crescimento ativo, foram feitas três amostragens. As partes apical, subapical e da base dos ramos foram separadas em casca, lenho (xilema) e gemas. O tempo médio de brotação (TMB) em condições controladas (25ºC), a umidade ponderal e a atividade das enzimas acima relacionadas foram determinadas. Os resultados obtidos reforçam a teoria de que o gradiente de brotação na nogueira se desenvolve durante a ecodormência e apresenta uma relação de dependência com a atividade da á-amilase; não está evidente a relação da atividade da SPS com a evolução do crescimento das gemas, durante a ecodormência.

Ozone effects on carbon metabolism in sensitive and insensitive Phaseolus cultivars

An ozone treatment of 165 nL L −1 for 3 h evoked differential responses in the primary leaves of two bean cultivars of the common bean ( Phaseolus vulgaris L.). While cv ‘Cannellino’ showed visible symptoms of injury within 24 h of exposure, no visible symptoms at all were evident in the cv ‘Top Crop’. In primary leaves of the sensitive cultivar Cannellino, we observed an increase in carbon breakdown (an increase in PFK and Fumarase) and a reduction in CO 2 photoassimilation, linked also to the diminished synthesis of sucrose (a decrease in SPS activity) and to the stimulation of the degradation of this sugar (an increase in SuSy and Invertase activities). A strong stimulation of PEPcase activity indicates both an increased synthesis of OAA and an enhanced replenishment of the tricarboxylic acid cycle. Finally, in Cannellino leaves the activity of NADP-malic enzyme increased indicating a stimulation of enzymes delivering NADPH. The findings of this research suggest that the visible symptoms in Cannellino represent an active response that this cultivar initiates to cope with excess oxidative load. The pattern in Top Crop was different. This cultivar did not show visible symptoms of injury, nor any responsive changes at the physiological and biochemical levels. Oxidative pathways are partially enhanced, e.g., increases in Invertase, PFK and IDH. There were also increases in some enzyme linked to the production of cytosolic NADPH as G6PD, probably caused by the slight increase in activity of the enzymes SKDH and PAL involved in synthesis of phenolic compounds. However, the absence of visible injury in Top Crop leaves is confirmation that, in this cultivar, the need to produce carbon skeleton and NADPH used in detoxification and repair process is lower.

Structure of Selenophosphate Synthetase Essential for Selenium Incorporation into Proteins and RNAs

AbstractSelenophosphate synthetase (SPS) catalyzes the activation of selenide with adenosine 5′-triphosphate (ATP) to generate selenophosphate, the essential reactive selenium donor for the formation of selenocysteine (Sec) and 2-selenouridine residues in proteins and RNAs, respectively. Many SPS are themselves Sec-containing proteins, in which Sec replaces Cys in the catalytically essential position (Sec/Cys). We solved the crystal structures of Aquifex aeolicus SPS and its complex with adenosine 5′-(α,β-methylene) triphosphate (AMPCPP). The ATP-binding site is formed at the subunit interface of the homodimer. Four Asp residues coordinate four metal ions to bind the phosphate groups of AMPCPP. In the free SPS structure, the two loop regions in the ATP-binding site are not ordered, and no enzyme-associated metal is observed. This suggests that ATP binding, metal binding, and the formation of their binding sites are interdependent. To identify the amino-acid residues that contribute to SPS activity, we prepared six mutants of SPS and examined their selenide-dependent ATP consumption. Mutational analyses revealed that Sec/Cys13 and Lys16 are essential. In SPS·AMPCPP, the N-terminal loop, including the two residues, assumes different conformations (“open” and “closed”) between the two subunits. The AMPCPP γ-phosphate group is solvent-accessible, suggesting that a putative nucleophile could attack the ATP γ-phosphate group to generate selenophosphate and adenosine 5′-diphosphate (ADP). Selenide attached to Sec/Cys13 as –Se–Se−/–S–Se− could serve as the nucleophile in the “closed” conformation. A water molecule, fixed close to the β-phosphate group, could function as the nucleophile in subsequent ADP hydrolysis to orthophosphate and adenosine 5′-monophosphate.

Differential regulation of grain sucrose accumulation and metabolism in Coffea arabica (Arabica) and Coffea canephora (Robusta) revealed through gene expression and enzyme activity analysis

* Coffea arabica (Arabica) and Coffea canephora (Robusta) are the two main cultivated species used for coffee bean production. Arabica genotypes generally produce a higher coffee quality than Robusta genotypes. Understanding the genetic basis for sucrose accumulation during coffee grain maturation is an important goal because sucrose is an important coffee flavor precursor. * Nine new Coffea genes encoding sucrose metabolism enzymes have been identified: sucrose phosphate synthase (CcSPS1, CcSPS2), sucrose phosphate phosphatase (CcSP1), cytoplasmic (CaInv3) and cell wall (CcInv4) invertases and four invertase inhibitors (CcInvI1, 2, 3, 4). * Activities and mRNA abundance of the sucrose metabolism enzymes were compared at different developmental stages in Arabica and Robusta grains, characterized by different sucrose contents in mature grain. * It is concluded that Robusta accumulates less sucrose than Arabica for two reasons: Robusta has higher sucrose synthase and acid invertase activities early in grain development - the expression of CcSS1 and CcInv2 appears to be crucial at this stage and Robusta has a lower SPS activity and low CcSPS1 expression at the final stages of grain development and hence has less capacity for sucrose re-synthesis. Regulation of vacuolar invertase CcInv2 activity by invertase inhibitors CcInvI2 and/or CcInvI3 during Arabica grain development is considered.

Postharvest Changes in the Activities of Sugar-metabolizing Enzymes in Cucumber Fruit Stored at Different Temperatures

This study investigated the postharvest changes in the activities of invertase (EC ; 3. 2. 1. 26), sucrose synthase (SS ; EC 2. 4. 1. 13) and sucrose phosphate synthase (SPS ; EC 4. 4. 1. 14) in cucumber fruits (Cucumis sativus L. cv. Project X) stored at 13 and 25°C for 20 days to understand the changes in fruit quality in relation to firmness and color after harvest. The acid invertase activities in the soluble and cell-wall-bound fractions in the cucumber stored at 25°C were significantly higher than those stored at 13°C from days 4 to 16. The acid invertase activity was 30-35 times higher than the SS activity on day 8 of storage at 25°C. The SS and SPS activities in the cucumber fruits stored at 25°C showed the highest activity on day 8. Low-temperature storage was effective in decreasing invertase activity in both fractions, thereby suppressing sucrose degradation. Low-temperature storage at 13°C caused no chilling injury to the cucumber. It was effective in maintaining sucrose content, color and firmness of cucumber fruits.

Postharvest Changes in the Activities of Sugar-metabolizing Enzymes in Eggplant Fruit Stored at Different Temperatures

In this study, we investigated the postharvest changes in the activities of invertase (EC 3.2. 1.26), sucrose synthase (SS; EC 2.4. 1.13) and sucrose phosphate synthase (SPS; EC 4.4. 1.14) and their relationships with sugar content during storage of eggplant (Solanum melongena L. cv. Senryou) fruit at 13 and 25°C for up to 14 days. Firmness and color change were used as the quality index of eggplant during storage. The acid invertase activity in the soluble fraction (SF) of the eggplants stored at 25°C was significantly higher than those of the eggplants stored at 13°C on days 11 and 14. In the cell-wall-bound fraction (CWBF), the activities were higher throughout the storage period. The acid invertase activity in the CWBF was 22-25 times higher than the SS activity on day 8 at 25°C. The SS and SPS activities in the eggplants stored at 25°C were the highest on day 14. Low-temperature storage was effective in decreasing invertase activity in both fractions, thereby suppressing sucrose degradation compared with high-temperature storage. Low-temperature storage at 13°C cause no chilling injury to the eggplant. It was even effective in maintaining the sucrose content, color and firmness of eggplant fruit.

Cloning and Characterization of a Sucrose Phosphate Synthase-encoding Gene from Muskmelon

Sucrose phosphate synthase [SPS (EC 2.4.1.14)] is thought to play a critical role in sucrose accumulation in muskmelon (Cucumis melo L.) fruit. A full-length cDNA clone encoding sucrose phosphate synthase was isolated from muskmelon by reverse transcriptase–polymerase chain reaction and rapid amplification of cDNA ends. The clone, designated CmSPS1, contains 3377 nucleotides with an open reading frame of 3162 nucleotides. The deduced 1054 amino acids sequence showed high identities with other plant sucrose phosphate synthases. Northern blot analysis indicated that CmSPS1 was expressed in leaves, stems, and mature fruit, but was not detected in roots or flowers. Moreover, the mRNA accumulation of CmSPS1 started at 25 days after pollination (DAP) and reached highest level in mature fruit. Interestingly, both sucrose content and SPS activity increased dramatically between 20 and 30 DAP during fruit development, suggesting that sucrose accumulation may be linked to the CmSPS1 transcript level in muskmelon fruit.

TRANSFORMASI GEN SUCROSE PHOSPHATE SYNTHASE (SoSPS1) MENGGUNAKAN Agrobacterium tumefaciens UNTUK MENINGKATKAN SINTESIS SUKROSA PADA TANAMAN TEBU (Saccharum officinarum L.)

Sucrose phosphate synthase (SPS EC 2.3.1.14) plays an important role in partition of assimilated carbon in most plants. SPS catalyses the penultimate reaction in the pathway of sucrose synthesis, in which sucrose-6-phosphate (Suc6P) is synthesized from UDPglucose (UDPG) and fructose-6-P (Fru6P). To increase the capacity of sugarcane in sucrose synthesis, spindle leaves of sugarcane cv R579 were transformed with cDNA SoSPS1 from sugarcane under the control of constitutive promoter (35S CaMV) that constructed in pBI 121 (pKYS) using Agrobacterium tumefaciens. Based on PCR analysis, we have detected the existence of SPS transgene in some lines of transformed sugarcane, called line 4, 5, 6, and 7. The SPS transgene in transformed sugarcane could be expressed into translation level and increased the amount of leaves SPS protein, so the activity of leaves SPS was higher than wild type sugarcane as control. The transformed sugarcane line 4, 5, 6, and 7 showed 1.4–2.9 fold increases in SPS activity and 1,76–2,2 fold increases in leaves sucrose content. Increasing in SPS activity in transgenic sugarcane was coupled by the increase in invertase activity and ratio between sucrose and starch content.

Alterations in photosynthesis in Arabidopsis lacking IMMUTANS, a chloroplast terminal oxidase

Green and white variegation in the Arabidopsis immutans (im) mutant is caused by a nuclear recessive gene. The green sectors contain cells with normal-appearing chloroplasts, while cells in the white sectors have photooxidized plastids lacking organized lamellae. In the present experiments, we found that the green im sectors have enhanced rates of carbon assimilation (monitored by (14)CO(2) uptake) and that there are corresponding increases in the activities of Rubisco and SPS, elevated starch and sucrose pool sizes, and an altered pattern of carbohydrate partitioning that favors sucrose over starch. We hypothesize that these increases are due, at least in part, to interactions with white sectors, perhaps to compensate for reductions in total source tissue. Consistent with this idea, the im white sectors accumulate low levels of sucrose and acid invertase activities are markedly increased in the white versus green cells. This suggests that there is a sucrose gradient between the green and white sectors, and that sucrose is transported from the green to white cells in response to sink demand. The expression of photosynthetic genes is not appreciably altered in the green im sectors versus wild type, but rather there is an up-regulation of genes involved in defense against oxidative stress and down-regulation of genes involved in cell wall biosynthesis. We postulate that changes in photosynthesis in the im green cells are driven by a need for photoprotection (especially early in chloroplast biogenesis) and due to source-sink interactions.

SPS Adsorption and Desorption during Copper Electrodeposition and Its Impact on PEG Adsorption

The adsorption and activation of bis (3-sulfopropyl)-disulfide (SPS) has been studied using a microfluidic electrochemical device. The device provides for accurate transitioning of solution over the working electrode allowing for addition or removal of additives from a base plating electrolyte. The transition from a plating bath to a polyethylene glycol bath shows a quick suppression of copper deposition similar to that seen with a bath. Acceleration at longer times, presumably by the activation of adsorbed SPS species, is a function of SPS concentration and applied cathodic potential. When copper is plated in the presence of SPS and for times around before the introduction of PEG, the activated SPS appears to inhibit the adsorption of PEG to the surface. System response to chloride ion addition or removal is relatively fast. Desorption of an activated layer occurs slowly, even at high cathodic potentials of , where current densities are over . Numerical simulations show that the time needed for PEG to saturate the bottom of a sub- feature is small relative to SPS activation times.

Frost resistance and biochemical changes during cold acclimation in different annual legumes

In Mediterranean areas of southern Europe growth of forages is seriously limited by the ability of each species to growth during cold winter. Therefore, the objective of this work was to prove the capacity for cold acclimation and frost resistance in four annual legumes native of Mediterranean region under laboratory conditions. Plants from subterranean clover ( Trifolium subterraneum L. ssp. brachycalycinum cv. Clare), balansa clover ( T. michelianum Savi cv. Giorgia), burr medic ( Medicago polymorpha L. cv. Anglona) and barrel medic ( M. truncatula Gaertn. cv. Paraggio) were cold acclimated by growing them at 10/5 °C. Non-acclimated plants developed at 20/15 °C. Dry matter partition, root solute content and enzymes for sucrose synthesis were determined during cold acclimation period. Freezing tolerance was determined by measuring the lethal temperature of 50% of the population (LT 50) and a thermal analysis was performed to study the dynamics for ice formation in plant tissues. Finally, by measuring forage production after 4 weeks at 20/15 °C it was assessed regrowth capacity. Cold-acclimated plants have increased root solute concentrations coupled with changes in the activity of some enzymes involved in sucrose synthesis in leaves. However, activities of sucrose synthesis pathway are not related with freezing tolerance in a simple way. Lower LT 50 was related to lower specific leaf area (SLA), higher root to shoot ratio and higher root solutes. Non-acclimated plants have LT 50 similar or higher than ice nucleation temperature indicating that these species cannot tolerate freezing. Cold acclimation decreased LT 50 in all species, being lower in Giorgia and Anglona; in Anglona did not change nucleation temperature, resulting values significantly higher than corresponding LT 50. This suggests that this cultivar was able to tolerate freezing. By contrast, in Giorgia, nucleation temperature decreased, which suggests that changes occurring during cold-acclimation might contribute to increase their capacity for avoidance by moderate supercooling. Cold-acclimated plants have higher regrowth capacity than non-acclimated ones except in Paraggio, which exhibited a poor regrowth. This might be due to an ineffective cold acclimation process related to impaired SPS activity and low starch reserves observed in this cultivar. On the other hand, Anglona and Giorgia have the better frost tolerance and higher potential for production of forage mass after freezing, indicating that they may be suitable cultivars for sow under cold winter conditions predominant in some Mediterranean zones.

Light regulation of sucrose-phosphate synthase activity in the freezing-tolerant grass Deschampsia antarctica

Deschampsia antarctica, a freezing-tolerant grass that has colonized the Maritime Antarctic, has an unusually high content of sucrose (Suc) in leaves, reaching up to 36% of dry weight. Suc accumulation has often been linked with increased activity of sucrose phosphate synthase (SPS; EC: 2.4.1.1.14). SPS, a key enzyme in sucrose biosynthesis, is controlled by an intricate hierarchy of regulatory mechanisms including allosteric modulators, reversible covalent modification in response to illumination, and transcriptional regulation. We hypothesized that during long day conditions in the Antarctic summer D. antarctica can maintain high SPS activity longer by indirect light regulation, thereby leading to a high sucrose accumulation in the leaves. The objectives of this study were to investigate a possible indirect light regulation of SPS activity and the effect of cold and day length on transcriptional and protein level of SPS in D. antarctica. Although SPS activity did not display an endogenous rhythm of activity in continuous light, activation of SPS at the end of the dark period was observed in D. antarctica. This activation of SPS is possibly controlled by covalent modification, because it was inhibited by okadaic acid while the SPS protein level did not significantly change. The highest SPS activity increase was observed after 21 days of cold-acclimation under long day conditions. This increased activity was not related to an increase in SPS gene expression or protein content. High SPS activity in cold long days leading to hyper accumulation of Suc appears to be among the features that permit D. antarctica to survive in the harsh Antarctic conditions.

EFFECTS OF DIFFERENT WATER TREATMENTS ON STARCH ACCUMULATION AND RELATED ENZYME ACTIVITY IN GRAIN OF MAIZE DURING GRAIN-FILLING PERIOD

Starch, one of the main products metabolized in the grain of maize, directly affects the yield and quality of maize. The synthesis of starch in maize grain is affected by the activities of several enzymes. We studied the effects of different water treatments on the grain starch content and components and related enzyme activity during the grain-filling period of two cultivars—the common corn, Yedan22, and the high oil corn, Gaoyou115. Three water treatments were chosen: W0 (no water irrigation after anthesis), W1 (irrigation one time after anthesis), W2 (irrigation two times after anthesis). The results showed that the patterns of starch accumulation and related enzyme activity were the same in the two cultivars, but their response to water treatments were different. Water duress significantly increased starch and amylopectin content and decreased amylose content in Yedan22, but increased the starch, amylopectin and amylose content in Gaoyou115. When sufficient levels of water were supplied, starch yield and its components significantly increased, as did the SS and SPS activities in ear leaves and ADPG-PPase, UDPG-PPase, SSS and GBSS activities in the grain, especially 10 to 30 days after anthesis. Increased enzyme activity in grain increased the amylopectin and amylose content in Gaoyou115. The activities of these enzymes in grain under water duress decreased early and quickly, and the activities of SPS, ADPG-PPase, and SSS were more sensitive to water duress than other enzymes.