ADP-glucose Pyrophosphorylase Research Articles

Effects of Red and Blue Light with Supplemental White Light on Growth, Carbohydrate Metabolism, and Yield of Virus-Free Potato in Plant Factories

The light spectrum has a strong effect on potato tuber development. To investigate the effect of varying the spectrum on potato tuber growth and yield, potato plantlets were transplanted under red/white light (RW; red light: 200 μmol m−2 s−1; white light: 100 μmol m−2 s−1), blue/white light (BW; blue light: 200 μmol m−2 s−1; white light: 100 μmol m−2 s−1), and white/red/blue light (WRB; white light: 100 μmol m−2 s−1; red light: 100 μmol m−2 s−1; blue light: 100 μmol m−2 s−1) with a 11/13-h (light/dark) photoperiod. Potato plants grown under RW had the highest mean fresh tuber weight and total yield among all treatments. Plants under RW resulted in the highest shoot dry weight at 30 d and 45 d among all treatments, providing a photosynthetic source for the tubers. Furthermore, the photosynthetic leaves under RW had a significantly higher total chlorophyll content than other treatments at 90 d. Plants under RW significantly increased tuber fresh weight per plant by 57.7% from 60 to 90 d. The spectrum of BW benefited potato bulking. Plants under BW at 40 d resulted in significant sucrose and starch changes between day and night compared with those at 20 d. BW had a positive effect on the activities of ADP-glucose pyrophosphorylase at 40 d and sucrose synthase at 60 d compared with RW and WRB during the day. Thus, the ratio of tuber (fresh weight of tuber ≥2.0 g) under BW was significantly higher than that under RW and WRB. The total yield of tubers under WRB was the lowest among all treatments.

Comprehensive analysis of AGPase genes uncovers their potential roles in starch biosynthesis in lotus seed

BackgroundStarch in the lotus seed contains a high proportion of amylose, which endows lotus seed a promising property in the development of hypoglycemic and low-glycemic index functional food. Currently, improving starch content is one of the major goals for seed-lotus breeding. ADP-glucose pyrophosphorylase (AGPase) plays an essential role in regulating starch biosynthesis in plants, but little is known about its characterization in lotus.ResultsWe describe the nutritional compositions of lotus seed among 30 varieties with starch as a major component. Comparative transcriptome analysis showed that AGPase genes were differentially expressed in two varieties (CA and JX) with significant different starch content. Seven putative AGPase genes were identified in the lotus genome (Nelumbo nucifera Gaertn.), which could be grouped into two subfamilies. Selective pressure analysis indicated that purifying selection acted as a vital force in the evolution of AGPase genes. Expression analysis revealed that lotus AGPase genes have varying expression patterns, with NnAGPL2a and NnAGPS1a as the most predominantly expressed, especially in seed and rhizome. NnAGPL2a and NnAGPS1a were co-expressed with a number of starch and sucrose metabolism pathway related genes, and their expressions were accompanied by increased AGPase activity and starch content in lotus seed.ConclusionsSeven AGPase genes were characterized in lotus, with NnAGPL2a and NnAGPS1a, as the key genes involved in starch biosynthesis in lotus seed. These results considerably extend our understanding on lotus AGPase genes and provide theoretical basis for breeding new lotus varieties with high-starch content.

Yield-related agronomic traits evaluation for hybrid wheat and relations of ethylene and polyamines biosynthesis to filling at the mid-grain filling stage

Because of the yield increase of 3.5–15% compared to conventional wheat, hybrid wheat is considered to be one of the main ways to greatly improve the wheat yield in the future. In this study, we performed a principal component analysis (PCA) on two-line hybrids wheat and their parents using the grain weight (GW), the length of spike (LS), the kernel number of spike (KSN), and spike number (SPN) as variables. The results showed that the variables could be classified into three main factors, the weight factor (factor 1), the quantity factor 1 (factor 2) and the quantity factor 2 (factor 3), which accounted for 37.1, 22.6 and 18.5%, respectively of the total variance in different agronomic variables, suggesting that the GW is an important indicator for evaluating hybrid combinations, and the grain weight of restorer line (RGW) could be used as a reference for parents selection. The hybrid combination with a higher score in factor 1 direction and larger mid-parent heterosis (MPH) of the GW and its parents were used to carry out the analysis of grain filling, 1-aminocylopropane-1-carboxylicacid (ACC) and polyamine synthesis related genes. The results suggested that the GW of superior grain was significantly higher than that of inferior grains in BS1453×JS1 (H) and its parents. Both grain types showed a weight of H between BS1453 (M) and JS1(R), and a larger MPH, which may be caused by their differences in the active filling stage and the grain filling rate. The ADP-glucose pyrophosphorylase (AGPase), granule bound starch synthase I (GBSSI), starch synthase III (SSS), and starch branching enzyme-I (SBE-I) expression levels of H were intermediated between M and R, which might be closely related to MPH formation of the GW. Compared with R and H, the GW of M at maturity was the lowest. The expression levels of spermidine synthase 2 (Spd2), ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (SAMDC) had significantly positive correlations with the grain filling rate (r=0.77*, 0.51*, 0.59*), suggesting their major roles in the grain filling and heterosis formation. These provide a theoretical basis for improving the GW of photo-thermo-sensitive male sterile lines (PTSMSL) by changing the endogenous polyamine synthesis in commercial applications.

The NAC transcription factor NAC019-A1 is a negative regulator of starch synthesis in wheat developing endosperm.

Starch is a major component of wheat (Triticum aestivum L.) endosperm and is an important part of the human diet. The functions of many starch synthesis genes have been elucidated. However, little is known about their regulatory mechanisms in wheat. Here, we identified a novel NAC transcription factor, TaNAC019-A1 (TraesCS3A02G077900), that negatively regulates starch synthesis in wheat and rice (Oryza sativa L.) endosperms. TaNAC019-A1 was highly expressed in the endosperm of developing grains and encoded a nucleus-localized transcriptional repressor. Overexpression of TaNAC019-A1 in rice and wheat led to significantly reduced starch content, kernel weight, and kernel width. The TaNAC019-A1-overexpression wheat lines had smaller A-type starch granules and fewer B-type starch granules than wild-type. Moreover, TaNAC019-A1 could directly bind to the 'ACGCAG' motif in the promoter regions of ADP-glucose pyrophosphorylase small subunit 1 (TaAGPS1-A1, TraesCS7A02G287400) and TaAGPS1-B1 (TraesCS7B02G183300) and repress their expression, thereby inhibiting starch synthesis in wheat endosperm. One haplotype of TaNAC019-B1 (TaNAC019-B1-Hap2, TraesCS3B02G092800) was positively associated with thousand-kernel weight and underwent positive selection during the Chinese wheat breeding process. Our data demonstrate that TaNAC019-A1 is a negative regulator of starch synthesis in wheat endosperm and provide novel insight into wheat yield improvement.

Functional characterization of a starch synthesis-related gene AmAGP in Amorphophallus muelleri

ABSTRACT Amorphophallus has attracted tremendous interest because of its high contents of glucomannan and starch. Very few genes regulating glucomannan and starch were reported in Amorphophallus. In this study, an ADP-glucose pyrophosphorylase (AGP) gene that plays a significant role in plant starch synthesis was cloned from Amorphophallus muelleri. It was shown that it encoded a predicted protein containing a conserved plant ADP-Glucose-PP repeat domain and seven potential ligand-binding sites. The real-time quantitative PCR showed that AmAGP was most abundant in tubers, and it was positively correlated with starch content. Additionally, its influencers about temperature and exogenous plant hormone were also discussed, showing that AmAGP expressed highly in tubers under treatments using 25°C and IAA. Furthermore, starch content was closely related to AmAGP expression level, suggesting that AmAGP was involved in the regulation of starch synthesis in A. muelleri. Therefore, identifying the sequence of AmAGP and its expression pattern during tuber enlarging and the changes of its transcript levels in response to temperature and plant hormones would contribute to a better understanding of starch synthesis, and also providing a reference information for future preferable breeding for obtaining more starch or more glucomannan in Amorphophallus.

Starch biosynthesis contributes to the maintenance of photosynthesis and leaf growth under drought stress in maize.

To understand the growth response to drought, we performed a proteomics study in the leaf growth zone of maize (Zea mays L.) seedlings and functionally characterized the role of starch biosynthesis in the regulation of growth, photosynthesis and antioxidant capacity, using the shrunken-2 mutant (sh2), defective in ADP-glucose pyrophosphorylase. Drought altered the abundance of 284 proteins overrepresented for photosynthesis, amino acid, sugar and starch metabolism, and redox-regulation. Changes in protein levels correlated with enzyme activities (increased ATP synthase, cysteine synthase, starch synthase, RuBisCo, peroxiredoxin, glutaredoxin, thioredoxin and decreased triosephosphate isomerase, ferredoxin, cellulose synthase activities, respectively) and metabolite concentrations (increased ATP, cysteine, glycine, serine, starch, proline and decreased cellulose levels). The sh2 mutant showed a reduced increase of starch levels under drought conditions, leading to soluble sugar starvation at the end of the night and correlating with an inhibition of leaf growth rates. Increased RuBisCo activity and pigment concentrations observed in WT, in response to drought, were lacking in the mutant, which suffered more oxidative damage and recovered more slowly after re-watering. These results demonstrate that starch biosynthesis contributes to maintaining leaf growth under drought stress and facilitates enhanced carbon acquisition upon recovery.

Glucosamine-P and rhodococcal ADP-glucose pyrophosphorylases: A hint to (re)discover (actino)bacterial amino sugar metabolism

Glycogen was described as a temporal storage molecule in rhodococci, interconnecting lipids and carbon availability. The Rhodococcus jostii ADP-glucose pyrophosphorylase (ADP-GlcPPase) kinetic and regulatory properties support this role. Curiously, the enzyme uses glucosamine-1P as alternative substrate. Herein, we report the in-depth study of glucosamine-1P activity and its regulation in two rhodocoocal ADP-GlcPPases, finding that glucosamine-6P (representing a metabolic carbon/nitrogen node) is a critical activator, then reinforcing the role of glycogen as an “intermediary metabolite” in rhodococci. Glucosamine-1P activity in rhodococcal ADP-GlcPPases responds to activation by metabolites improving their catalytic performance, strongly suggesting its metabolic feasibility. This work supports a scenario for new molecules/metabolites discovery and hypothesizes on evolutionary mechanisms underlying enzyme promiscuity opening novel metabolic features in (actino)bacteria.

Differential regulation of enzyme activities and physio-anatomical aspects of calcium nutrition in grapevine

It remains true that through its signaling mechanisms, Ca2+ also has specific, direct effects on plant metabolic activities, which are poorly understood due to the currently trendy pursuit of Ca2+ signaling studies. This paucity triggered us to examine the virtues of calcium nutrition by investigating carbohydrate metabolism using combinations of physiological and microscopy techniques in Ca2+ sufficient and Ca2+ starved grapevines (Vitis vinifera L.). Net photosynthesis was severely down-regulated in Ca2+ deficient vines, which paralleled with altered chloroplast ultrastructure and reduced chlorophyll concentration. Interestingly, the activities of Rubisco, sucrose phosphate synthase (SPS), sucrose synthase (SS), and fructose-1, 6-bisphosphatase (FBPase) were elevated in Ca2+ deficient vines, while ADP-glucose pyrophosphorylase (AGPase) and phosphoribulose kinase (PRK) activities were reduced. Since plants evolved adaptive mechanisms to cope up with lack or excess of nutrients, these metabolic changes in Ca2+ deficient and sufficient grapevines could be interpreted as acclimation reactions to establish optimal homeostasis. However, given the controversial nature of calcium’s multifunctionality, we need concrete evidence for this radical new paradigm.

Phosphorylation of ADP-Glucose Pyrophosphorylase During Wheat Seeds Development.

Starch is the dominant reserve polysaccharide accumulated in the seed of grasses (like wheat). It is the most common carbohydrate in the human diet and a material applied to the bioplastics and biofuels industry. Hence, the complete understanding of starch metabolism is critical to design rational strategies to improve its allocation in plant reserve tissues. ADP-glucose pyrophosphorylase (ADP-Glc PPase) catalyzes the key (regulated) step in the synthetic starch pathway. The enzyme comprises a small (S) and a large (L) subunit forming an S2L2 heterotetramer, which is allosterically regulated by orthophosphate, fructose-6P, and 3P-glycerate. ADP-Glc PPase was found in a phosphorylated state in extracts from wheat seeds. The amount of the phosphorylated protein increased along with the development of the seed and correlated with relative increases of the enzyme activity and starch content. Conversely, this post-translational modification was absent in seeds from Ricinus communis. In vitro, the recombinant ADP-Glc PPase from wheat endosperm was phosphorylated by wheat seed extracts as well as by recombinant Ca2+-dependent plant protein kinases. Further analysis showed that the preferential phosphorylation takes place on the L subunit. Results suggest that the ADP-Glc PPase is a phosphorylation target in seeds from grasses but not from oleaginous plants. Accompanying seed maturation and starch accumulation, a combined regulation of ADP-Glc PPase by metabolites and phosphorylation may provide an enzyme with stable levels of activity. Such concerted modulation would drive carbon skeletons to the synthesis of starch for its long-term storage, which later support seed germination.

Starch content and activities of starch biosynthetic enzymes in wheat, rice and millets

The aim of the study was to correlate the accumulation of amylose and total starch with activities of starch biosynthetic enzymes (AGPase, SSS and GBSS) in cereals like rice (PB-2, PD-19), wheat (UP-262, PBW-343) and millets (Barnyard millet, Finger millet and Foxtail millet) at different stages of endosperm development. ADP-glucose pyrophosphorylase (AGPase) activity was found higher in all varieties during developmental stage followed by granule bound starch synthase (GBSS) and soluble starch synthase (SSS). Accumulation of amylose was positively influenced by activity of AGPase and GBSS. Total starch accumulation was positively correlated with activity of AGPase and SSS. In all these varieties rate of enzymes activity was found higher at S3 stage. Higher ratio of AGPase and GBSS contributes lesser resistant starch, amylose content and am/ap ratio. Ratio of AGPase and GBSS can be used as an index for amylose content when it was studied in large sample size of similar varieties.

22KD Zein Content Coordinates Transcriptional Activity during Starch Synthesis in Maize Endosperm

Starch, the main form of stored energy in plants, plays an important role in maize (Zea mays L.) kernel development. The Shrunken-2 (Sh2) gene encodes the large subunit of the rate-limiting starch biosynthetic enzyme ADP-glucose pyrophosphorylase (AGPase). The sh2 mutant exhibits impaired AGPase activity, resulting in the partial or complete loss of starch synthesis. Here, we investigated the transcriptional regulatory framework of sh2 through transcriptome and co-expression network analysis using an F2 population derived from the maize reference line B73 and sweet corn inbred line HZ508. We identified 5175 differentially expressed genes (DEGs), including 2878 upregulated and 2297 downregulated genes in sh2 mutant lines. DEGs are associated with various biological processes including nutrient reservoir activity, transferase activity, catalytic activity, water deprivation and glycogen metabolism. At the genetic level, 2465 DEGs, including 357 transcription factors, were involved in transcription. In addition, the maize floury and opaque mutant genes fl1, ndk2, o7 and o2, which regulate the biosynthesis of 22KD zein, were co-expressed with the differential expressed transcription factor genes, thus suggesting that zein content might be a key regulator coordinating the expression of genes determining starch accumulation in maize endosperm.

Changes in carbohydrate metabolism and endogenous hormone regulation during bulblet initiation and development in Lycoris radiata

BackgroundLycoris species have great ornamental and medicinal values; however, their low regeneration efficiency seriously restricts their commercial production. Understanding the mechanism of bulblet propagation in this genus, which has remained underexplored to date, could provide a theoretical basis for improving the reproductive efficiency. Therefore, we studied the bulblet initiation and developmental processes in Lycoris radiata.ResultsWe found that bulblets are formed on the junctions of the innermost layers of scales and the basal plate, and initially present as an axillary bud and gradually develop into a bulblet. We also determined the changes in carbohydrate and endogenous hormone contents during bulblet initiation and development, as well as the expression patterns of genes involved in carbohydrate metabolism and hormone biosynthesis and signaling through transcriptome analysis. Soluble sugars derived from starch degradation in the outer scales are transported to and promote bulblet initiation and development through starch synthesis in the inner scales. This process is mediated by several genes involved in carbohydrate metabolism, especially genes encoding ADP glucose pyrophosphorylase, a crucial starch synthesis enzyme. As for hormones, endogenous IAA, GA, and ABA content showed an increase and decrease during bulblet initiation and development, respectively, which were consistent with the expression patterns of genes involved in IAA, GA, and ABA synthesis and signal transduction. In addition, a decrease in ZR content may be down- and up-regulated by CK biosynthesis and degradation related genes, respectively, with increasing auxin content. Furthermore, expression levels of genes related to BR, JA, and SA biosynthesis were increased, while that of ethylene biosynthesis genes was decreased, which was also consistent with the expression patterns of their signal transduction genes.ConclusionsThe present study provides insights into the effect of carbohydrate metabolism and endogenous hormone regulation on control of L. radiata bulblet initiation and development. Based on the results, we propose several suggestions to improve L. radiata propagation efficiency in production, which will provide directions for future research.

Differential carbohydrate dynamics in Arabidopsis wild-type and ntrc mutant after trehalose feeding

The trehalose sugar plays pivotal roles in plants. In Arabidopsis, trehalose supplied to the medium leads to starch accumulation through redox activation of the ADP-glucose pyrophosphorylase (AGPase) by the NADPH-dependent thioredoxin reductase C (NTRC). To gain further insight on the regulation of carbohydrate metabolism by trehalose and NTRC, Arabidopsis wild-type (wt) and ntrc plants were raised in the MS medium supplemented with or without 100-mM sucrose or trehalose and alterations in sugar and starch contents as well as the activities and expressions of some carbohydrate metabolizing enzymes were investigated. The ntrc plants displayed lower growth rate compared to wt by sugar feeding. Under trehalose treatment, the total soluble, reducing and non-reducing sugars of wt and ntrc plants decreased between end of the day and end of the night, but starch in the ntrc plants remained unaltered during the aforementioned period. The obtained data showed that trehalase activity and gene expression display diurnal rhythms. Meanwhile, under darkness, trehalase gene expression required functional NTRC. Trehalose feeding induced NTRC expression during the day, but suppressed it during the night. Moreover, AGPase expression found to be jointly regulated by carbon nutrition and the light–dark period in both wt and mutant plants. The current data also revealed that AMY3 (α-amylase 3) gene expression depends on the presence of functional NTRC in plants. It seems that cross-talk between trehalose and NTRC regulates diurnal carbohydrate metabolism in plants.

A New SNP in Rice Gene Encoding Pyruvate Phosphate Dikinase (PPDK) Associated with Floury Endosperm.

Rice varieties with suitable flour-making qualities are required to promote the rice processed-food industry and to boost rice consumption. A rice mutation, Namil(SA)-flo1, produces grains with floury endosperm. Overall, grains with low grain hardness, low starch damage, and fine particle size are more suitable for use in flour processing grains with waxy, dull endosperm with normal grain hardness and a high amylose content. In this study, fine mapping found a C to T single nucleotide polymorphism (SNP) in exon 2 of the gene encoding cytosolic pyruvate phosphate dikinase (cyOsPPDK). The SNP resulted in a change of serine to phenylalanine acid at amino acid position 101. The gene was named FLOURY ENDOSPERM 4-5 (FLO4-5). Co-segregation analysis with the developed cleaved amplified polymorphic sequence (CAPS) markers revealed co-segregation between the floury phenotype and the flo4-5. This CAPS marker could be applied directly for marker-assisted selection. Real-time RT-PCR experiments revealed that PPDK was expressed at considerably higher levels in the flo4-5 mutant than in the wild type during the grain filling stage. Plastid ADP-glucose pyrophosphorylase small subunit (AGPS2a and AGPS2b) and soluble starch synthase (SSIIb and SSIIc) also exhibited enhanced expression in the flo4-5 mutant.

Split application enhances sweetpotato starch production by regulating the conversion of sucrose to starch under reduced nitrogen supply

Split application could improve nitrogen (N) uptake and increase sweetpotato yields under reduced N supply; however, little is known about how it affects the process of starch production in storage roots. An experiment was conducted to determine the effects of three N management strategies [conventional basal N management; 80% of the conventional N rate applied as a basal fertilizer; 80% of the conventional N rate equally split at transplanting and 35 days after transplanting] on starch accumulation, enzyme activity and genes expression in the conversion of sucrose to starch and the relationships among them. The results showed that, compared with conventional basal N management, split application decreased sucrose accumulation by 11.78%, but increased starch accumulation by 11.12% through improving the starch accumulation rate under reduced N supply. The ratio of sucrose synthetase to sucrose phosphate synthase, the enzymatic activity of ADP-glucose pyrophosphorylase (AGPP), starch synthase, and the expression of their corresponding genes were promoted by split application under reduced N supply and were positively correlated with starch accumulation rate. AGPP is the rate-limiting enzyme in starch synthesis in storage roots under different N management strategies. These results indicate that starch accumulation was enhanced by split application through regulating the activity and gene expression of key enzymes involved in the conversion of sucrose to starch under reduced N supply.

Exogenous melatonin improves cotton (Gossypium hirsutum L.) pollen fertility under drought by regulating carbohydrate metabolism in male tissues

Although exogenous melatonin can enhance the drought tolerance of plants, reports on the role of melatonin in drought tolerance in male reproductive organs are limited. To explore this, a pot experiment was conducted with cotton cultivar Yuzaomian 9110 to study the effects of exogenous melatonin (100, 200, and 1000 μM) on male fertility and related carbohydrate metabolism in anther under drought. Results showed that drought inhibited the translocation of carbon assimilates to anthers, however, melatonin application (100 and 200 μM) significantly improved the translocation of carbon assimilates to drought-stressed anthers. Drought reduced the deposition of starch, the hydrolysis of sucrose into hexoses, the generation of adenosine triphosphate (ATP) in anthers, restricting pollen viability and germination. Nevertheless, the appropriate melatonin concentrations (100 and 200 μM) increased the starch accumulation by enhancing ADP-glucose pyrophosphorylase and soluble starch synthases activities and accelerated the hydrolysis of sucrose by increasing sucrose synthase, acid and alkaline invertases activities in drought-stressed anthers. Appropriate melatonin concentrations (100 and 200 μM) also could help to generate more ATP for reproductive activities of drought-stressed anthers, finally increasing the pollen viability and germination of drought-stressed plants. These findings suggest that drought inhibited male fertility of cotton, but a precise melatonin application could regulate the carbohydrate balance of drought-stressed anthers to improve male fertility. This is the first report demonstrating the important role of exogenous melatonin in improving male fertility under drought conditions by regulating the carbohydrate metabolism in the male part of cotton.

Development and identification of three functional markers associated with starch content in lotus (Nelumbo nucifera)

It have been significantly demonstrated that Hexokinase (HXK), Granule-bound starch synthase (GBSS) and ADP-glucose pyrophosphorylase (AGPase) are three critical enzymes in the starch biosynthetic pathway and are related to starch (amylose, amylopectin and total starch) content in lotus. It is important to develop functional markers in marker-assisted selection of lotus breeding. So far there have been few reports about lotus functional markers. In this study, based on insertion-deletions (INDELs) and single-nucleotide polymorphisms (SNPs), we developed three functional markers, FMHXK-E1, FMGBSS-I8 and FMAGPL-I1. FMHXK-E1 was developed based on polymorphisms of two haplotypes of NnHXK. 26 lotus cultivars that the 320-bp fragment presented in NnHXK had a lower content of amylose and a higher content of amylopectin. FMGBSS-I8 was developed based on polymorphisms of two haplotypes of NnGBSS. The group containing 32 lotus cultivars with the 210-bp fragment had less amylose content and more amylopectin content. FMAGPL-I1 was developed based on polymorphisms of two haplotypes of NnAGPL (ADP-glucose pyrophosphorylase large subunit gene). The group containing 40 lotus cultivars with the 362-bp fragment had less amylopectin, total starch content and more amylose content. According to the study, FMHXK-E1, FMGBSS-I8 and FMAGPL-I1 are closely related to lotus starch content. It could be provided research basis for molecular assisted selection of lotus starch content improve breeding efficiency.

Effects of foliar application of magnesium sulfate on photosynthetic characteristics, dry matter accumulation and its translocation, and carbohydrate metabolism in grain during wheat grain filling

Our previous studies showed that foliar applied magnesium sulfate during the booting stage can effectively increase wheat grain weight. To explore the effects of foliar application of magnesium sulfate during wheat grain filling on photosynthetic characteristics of flag leaf and grain filling, an experiment was conducted using winter wheat cultivars to assess the effects of foliar application of magnesium sulphate on photosynthetic characteristics of flag leaves, carbohydrate metabolism in grains, and dry matter translocation in different organs in the Zhoumai 27 and Aikang 58 cultivars at different growth stages. The results indicated throughout the different stages of growth, the flag leaves exhibited a high net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration (Tr), and a decrease in the concentration of intercellular CO2 (Ci). Therefore, foliar application of magnesium sulfate during the booting stage maintained high canopy photosynthesis after anthesis. Simultaneously, exogenous supply of magnesium sulphate enhanced the sucrose synthase (SUS) and invertase (INV) enzyme activities in detached wheat grains, meanwhile reinforced the activities of most starch synthesis enzyme such as ADP-glucose pyrophosphorylase and soluble starch synthase, and consequently lead to a higher content of grain starch. Furthermore, field experiment also confirmed foliar application of magnesium sulphate can improve superior dry matter accumulation and translocation in grain.

Transcriptome Analysis and Identification of Genes Associated with Starch Metabolism in Castanea henryi Seed (Fagaceae).

Starch is the most important form of carbohydrate storage and is the major energy reserve in some seeds, especially Castanea henryi. Seed germination is the beginning of the plant’s life cycle, and starch metabolism is important for seed germination. As a complex metabolic pathway, the regulation of starch metabolism in C. henryi is still poorly understood. To explore the mechanism of starch metabolism during the germination of C. henryi, we conducted a comparative gene expression analysis at the transcriptional level using RNA-seq across four different germination stages, and analyzed the changes in the starch and soluble sugar contents. The results showed that the starch content increased in 0–10 days and decreased in 10–35 days, while the soluble sugar content continuously decreased in 0–30 days and increased in 30–35 days. We identified 49 candidate genes that may be associated with starch and sucrose metabolism. Three ADP-glucose pyrophosphorylase (AGPase) genes, two nucleotide pyrophosphatase/phosphodiesterases (NPPS) genes and three starch synthases (SS) genes may be related to starch accumulation. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to validate the expression levels of these genes. Our study combined transcriptome data with physiological and biochemical data, revealing potential candidate genes that affect starch metabolism during seed germination, and provides important data about starch metabolism and seed germination in seed plants.

On the simultaneous activation of Agrobacterium tumefaciens ADP-glucose pyrophosphorylase by pyruvate and fructose 6-phosphate

Bacterial ADP-glucose pyrophosphorylases are allosterically regulated by metabolites that are key intermediates of central pathways in the respective microorganism. Pyruvate (Pyr) and fructose 6-phosphate (Fru6P) activate the enzyme from Agrobacterium tumefaciens by increasing Vmax about 10- and 20-fold, respectively. Here, we studied the combined effect of both metabolites on the enzyme activation. Our results support a model in which there is a synergistic binding of these two activators to two distinct sites and that each activator leads the enzyme to distinct active forms with different properties. In presence of both activators, Pyr had a catalytically dominant effect over Fru6P determining the active conformational state. By mutagenesis we obtained enzyme variants still sensitive to Pyr activation, but in which the allosteric signal by Fru6P was disrupted. This indicated that the activation mechanism for each effector was not the same. The ability for this enzyme to have more than one allosteric activator site, active forms, and allosteric signaling mechanisms is critical to expand the evolvability of its regulation. These synergistic interactions between allosteric activators may represent a feature in other allosteric enzymes.